Has anyone had experience trying to get the European horsepower out of a US model K75? As I understand it, the American model was limited in order to comply with emissions standards. Is this a re-map of the ECU, a different CAM, or just plain impossible / not worth it?

Inaccurate data removed.

Did they simply change to K100 pistons to do that or make a change to the head? 

Racing guys put K75 pistons into their K100 to increase the compression ratio.

I have always read and understood that K75 models - all years and markets - had 11.0:1 compression ratio both before and after the piston rings being 'pinned' for less oil burning when the end gaps would 'float' to the bottom allowing some oil to pass into the combustion chamber, circa 1988. As the bore is the same size as a K100 8V the K75 pistons slot right in. K100 8V had a 10.2:1 compression ratio.

For fun, here's a dyno run between a 1987 and a '92 K75...

Dyno Run Duelling K75

You might try disassembly of the stock TBs to fit three of the four 38mm K1200RS/GT (without cruise control) TBs, and then a reduced backpressure exhaust canister out back. No reason to change the air filter as the stock size does all the flowing it can. I once heard a rumour/theory/myth/outright lie that a K75 can reach 90 crank HP this way and one day I'm going to cobble one together like this to see if I can ruin its otherwise wonderful tractability this way.

It's a while since I read up on it,  but I thought European horsepower was a reference to the k100, with earlier models having hotter cams, and later models different cams to comply with US exhaust regs (or was it Californie..i..a)

The higher compression for the k75 results in k75=75 horseys, easy to remember. The k100 doesn't reach that.

A K100 doesn't make 75 hp? 

brickrider2 wrote:A K100 doesn't make 75 hp? 

Not in Switzerland, but, yes 90 crank HP in other markets.

True I meant the ratio,  if the k100 was as good it would mean k100=100horseys. I don't much remember numbers unless they're easy round ones.

Please don't ask me if 75 is a round number.

You gotta get the 16 valve version to get all 100.

daveyson wrote:Please don't ask me if 75 is a round number.

Well, if we come at the task using numerology... 7 & 5 = 12. 1 & 2 = 3. 3 is a nice triangular, roundish number. Sold!

Pick a number between 1 and 10

Add 175

Subtract 75

Subtract the number you first thought of

By the magic power of round numbers the answer is 100

That's the number of horseys in a 16V K100. Coincidence?

If you want horse power from a K75 get rid of the rev limiter they turn into little screamers

daveyson wrote:It's a while since I read up on it,  but I thought European horsepower was a reference to the k100, with earlier models having hotter cams, and later models different cams to comply with US exhaust regs (or was it Californie..i..a)

The higher compression for the k75 results in k75=75 horseys, easy to remember. The k100 doesn't reach that.

Having 3 2v K100s, as in 83 K100RS, 84 K100RT and 92 K100LT.......the 83 and 84 Ks both have the vacuum sensor to advance ignition timing, the 92 K100LT does not have this. The 84 RT felt much more lively than the 92 LT.

But, the 83 RS is in a different league, cam profiles are the difference and it also has the visible engineering screws on the cam cover. Its much more lively than my K1100LT and I have 2 of those to compare it. I have not tried to find out if there is a difference in bhp....

I am only aware of 2 compression ratios, one for K75 and one for K100. Detuning is achieved by other means than altering pistons and compression ratios.

Directly below is a link to a prior discussion about K100-16V, K1 & K1100 camshafts. Post 18 is where I drew up a list of variables:

16V Camshafts link

Early K100 used 284 degree cams. They were still using these through 1989 on Std K100 and RS, and continued using them to the end of 8V production on LT/RT. California models 'always' used milder 256 degree cams. Swiss market K100 also used a 284 degree cam but with different part numbers.
11 31 1 460 045 Intake - Rest of the world
11 31 1 460 044 Exhaust - Rest of the world
11 31 1 461 525 Intake - CA
11 31 1 461 526 Exhaust - CA
11 31 1 464 000 Intake - Swiss
11 31 1 464 001 Exhaust - Swiss

I located an old parts official SNAB book (BMW's paper spare parts catalogue from before fische and ETK) on a back shelf at work the other day (printed late 1984) and it doesn't show a different part number on camshafts from early to late K100 models, either US or Rest of the World, as they used to list things. I think we're still being tugged and pulled at by that author from decades ago who suggested in jest at a rally seminar that the first year US 1985 (therefore, 1983, '84 & '85 Euro models) K100 were "the finest year". BTW, I was living near Greenfield Massachusetts when this rally was on but did not attend the seminar mentioned below.
As for why early models feel faster, it must be something in the water.


"Dave is absolutely correct. The story is kinda funny.

I was asked to give a K-tech session at the RA National Rally in Greenfield MA some years ago. (Dave was Chair of that rally..)

At the time, I owned an '85 K100RT, and was somewhat defensive about the scorn heaped upon the '85s by owners of later K's.

During the tech session, several people made somewhat disparaging remarks about the '85 K.. and finally in response to one of the remarks I sarcastically said "Oh - you mean the FINEST YEAR K?"

It got rather a large laugh and I thought that would be the end of it.. but I started referring to my K as the FYK100RT in messages to the IBMWR mailing list.

The name stuck. I started seeing it used in ads for '85 K bikes, it started appearing in people's SIGs on messages, and questions like this started popping up - "Why is the '85 the Finest Year K?" I've even seen it used in articles in a certain national club magazine 

As Paul Harvey would say - now you know the rest of the story.. 

Oh - the '85 K100's had one advantage over later K100's (until the 4V engine) - they were the "fastest" ones. They had a euro intake cam (except in California) that gave a real 90HP. Starting in '86 all K100's received the California intake cam (Edit: not true according to clear BMW ETK listings. California models were the only ones to have 256 cams both intake & exhaust) that gave about 5 less HP - but BMW never changed the specifications.

There were some features that BMW did improve with later K100's - heat management was generally better (but still awful on an RT) and buzz/vibration was reduced a bit... but the '85 bikes were a real bargain since you could usually find one for $1,000 or more cheaper than the same bike as an '86. This changed as the FYK rumour spread 

Best, 
Don Eilenberger http://www.eilenberger.net 
Spring Lk Heights NJ NJ Shore BMW Riders"

That's a great, well-researched post.
Now I'm not saying anything to the contrary - I'm definitely not saying anything to the contrary.

But...
BMW have on occasion had the habit of upgrading a part, and leaving the part number unchanged. I know this because I had a problem with dropped valves on an oilhead boxer - long story - but it turned out that BMW upgraded/improved the valve spring retainer, which is obvious in comparison, but did not change the part number. They also modified the pushrods and made them heavier, but again no alteration to part number.

Now all of this was brought to my attention by someone in the trade. I've measured and seen the above two examples, but apparently, there are numerous other examples of this kind of carry-on from that Bayerischen crew. A cynic might conclude that it's a liability thing, but that'd just be a cynic's conclusion...

I've got an '84 K100 btw and it does go like stink, but then it has got a 89-onwards lighter crank.

It is absolutely true that Bay Em Vay change part designs without changing part numbers. To wit, the large, caged bearing in Paralever final drives is an example. When they were having dramas regularly with them they did not supersede the part number, even though the number of ball bearings inside changed. It was only years later that the number changed, after the hullabaloo of inherent bad design and subsequent failure had died down a bit. This could be a factor here with camshafts, might, perhaps, maybe, sure. WWNK.

Some years ago, whilst attending a BMW dinner in South Carolina after a yearly business meeting and test ride of the brand spanking new dog of a motorbike, the R1200CLC (I was a lowly parts manager but the dealer principal from our shop could not attend so he asked me to stay on for the business portion of the week), Frank Stevens from BMWNA, with a cocktail or three in him, was fielding questions from various shop owners. He said some remarkable things. One of them was an obvious, in reference to superseded part numbers, etc., "Do you expect us to open ourselves up to lawsuits!?"

Unless, someone has two previously untouched engines, from the years in question, apart and is willing to whip calliper and micrometre out and give 'em a bloody good going over to compare.

Chris846
"I've got an '84 K100 btw and it does go like stink, but then it has got a 89-onwards lighter crank."


10.3 kg (22.71 lbs) down to 8.95 kg (19.73 lbs) mid-year '89 production is a perty good ol' drop in spinning mass!

For further interest in the original subject, here's a list of K75 camshafts, all years, variants & markets. No degrees are included.

K75, C, RT, S
11 31 1 460 617 Intake
11 31 1 460 618 Exhaust

Why change a good thing?

I get that too. I have 2 K7s at the mo - the madass and the K75k. Feel quite different - the K75k is punchy, but seems to take forever to rev out. Both are identical insofar as exhaust/intake/ignition advance etc. If the supercharger project comes to anything then I aim to dyno the engine before/during/afterwards, and educate myself. Seat of the pants can be very deceptive. Best example is messing with the intake: if (as is quite likely) you ruin the mid-range, then the sudden pick up when it starts to breathe properly/overcomes your handiwork/makes a lot more noise than before, can feel like a surge in power.

Often when someone at the shop enquires about go-fast goodies for their new Beemer or Ducati I first steer them towards thinking about weight savings. I'd love to sell you a Power Commander V & Termignoni full system, but eliminating that extra piled on plate at the all-you-can-eat-all-American-buffet table before your ride can make a world of difference. Some twig to what I'm suggesting, and I haven't been sucker punched yet.

If you want to make the 100s go quicker for a couple of hours work, then do what quite a few on this forum have done (including me). Fit K1100 throttlebodies - you might need a new throttle cable too but that seems to be pot-luck on which cable quadrant you get on the tb stack - and advance the timing by six degrees (4mm on the hall sensor plate). The result is a shitload more punch in the midrange and it's not the ass-dyno kicking in. I compared an utterly standard '87 K100 back-to-back with my modified '83 K100, both equipped with RS fairings; at 50mph in third gear and nailing the throttle the standard bike felt like a paraplegic donkey.

Yeah, Dai, I can confirm that that TB swap is ideal, 33mm for 35's. I did it ten years ago on my red K100RS. I never bothered to modify the TPS connection (or even hook it up) and with the slightly more free-flowing Motad exhaust it's a lively beasty when giving it a good caning at mid-RPM. It helps to have a modified ignition box, too. No rev limit means she sings into the red zone and keeps pulling. I once saw 255km/h (indicated) on a flat, dead-straight country road in New South Wales. I imagined errant wallabies and savoured the speed for only a little minute.

Saw that speed come up on a Moto Guzzi Daytona 'B' once and it was still pulling...then I threw the bloody big anchor out the back in a panic because the roundabout on the horizon wasn't on the horizon any more   Nowadays that particular dual carriageway down in Dorset is more often nose-to-tail than clear. A bit more dangerous than wallabies.

Laitch wrote:According to Anton Largiader at Virginia Motorrad, the compression ratio was changed from 11.0:1 to 10.5:1 in 1986, lowering horsepower and torque, but it looks like the reduction happened to the K100 instead.

This is a question i stumbled upon. Most sources online give K75 compression ratio of 11.0 : 1. How ever wikipedia states both 11.0 : 1 and 10.5 : 1. From tech page the marketing says in year 1986 11.0 : 1 ratio but later ones seem to always state 10.5 : 1. Any thought on this? Mostly it is said that K75 is more efficient because higher comp ratio but K100 10.2 versus 10.5 on K75 doesnt seem big deal.
This makes me kinda sad because I always thought of having high (for the time) ratio of 11. Now it doesn't feel as sporty as it used to

On the mehanical side it would seem that pre -86 K75 has different pistons than later ones. Or is the chamber of different geometry . Any ideas on this?

Anyway if this is the case, it makes me wonder why they made such change? Too prone to knock at the time of phasing out toxic leaded fuels?

My 86 Luftmeister Turbo K75 also has Lufty high performance cams. Since it's an antique turbo it doesn't kick until above 4,000 but below 4,000 the Lufty cams do make a noticeable difference compared to my K75s with stock cams. So it's American K75 horsepower you're looking for, not European.

See page 4 in this PDF:
http://dws.epizy.com/ktech/Luftmeister.1988.Catalog.OCRc.pdf

There's a decked and ported K75 that used to show up on Craig's List in Seattle every few years. I kick myself for not buying it.

I believe the K75 has a domed piston with valve interference as opposed to the K100 that doesn't.

I suspect this was to increase the compression ratio slightly to get a small increase i power output.  With the race for power output at the time, I suspect it was to keeep the smaller K75 engine competitive with the Japanese 750's. 

I have heard that the K100 power output, on the other hand, was limited by European regulations so the higher output from increased compression wasn't necessary. 

I have heard that there have been engine builders who replaced K100 pistons with K75 pistons to increase power output for racing.

I am pretty sure of the accuracy of the above, I may be mistaken, and if I am, the Duck will be here soon to make corrections.

Point-Seven-five wrote:I have heard that the K100 power output, on the other hand, was limited by European regulations so the higher output from increased compression wasn't necessary. 

My understanding is that happened when the 4V Ks come out in order to adhere to a voluntary limit of 100 hp. When they went from 1000 ccs of the K1/K100RS4V to K1100s the max horsepower remained at 100 so that's a pretty good indicator that the K1100 cams and/or fuel mapping are detuned.

Are there any German members here who can comment on German regulations on power output for motorcycle engines in the early/mid 80's.  I seem to recall reading something about limits on engine output at the time.

Point-Seven-five wrote:I believe the K75 has a domed piston with valve interference as opposed to the K100 that doesn't.

I suspect this was to increase the compression ratio slightly to get a small increase i power output.  With the race for power output at the time, I suspect it was to keeep the smaller K75 engine competitive with the Japanese 750's. 

I have heard that the K100 power output, on the other hand, was limited by European regulations so the higher output from increased compression wasn't necessary. 

I have heard that there have been engine builders who replaced K100 pistons with K75 pistons to increase power output for racing.

I am pretty sure of the accuracy of the above, I may be mistaken, and if I am, the Duck will be here soon to make corrections.

This thread came up again and I have made some posts in it. You would be correct in all these. Particularly the voluntary code in Germany to limit bikes to 100bhp as they feared an EU imposed limit...resulting in K engines having a lot of torque.

But interestingly due to a recurrence of Kpox yet another K landed my way.

Now I already have a 1983 K100RS and a 1984 K100RT. So now I have a 1983/4 K100 that was called RS but in fact was a naked K100 with a Sprint fairing. 

1983 K100RS: Engine 48/83, Has engineering screws, has vacuum sensor, 31/11 final drive
1984 K100RT: Engine 32/84, No engineering screws, has vacuum sensor and 32/11 final drive.
1984 K100: Engine appears 38/83. No engineering screws, has vacuum sensor, 32/11 final drive.

The RS is definitely the pick of the bunch for performance by a significanty margin. But I am puzzled by why the apparently earlier engine in the K100 has no engineering screws compared with the later engine K100RS. 

The thing is that the 83 RS does feel to have a significantly higher performance than not just the RT but also the Sprint faired naked bike that is supposed to be mechanically identical.

My local ex BMW guru friend passed in November 2021 and he had commented that parts changed but part nos did not, specifically referring to camshafts. Interestingly he said that the only reason he ended up taking heads off Ks at the delership was accident damage and not mechanical failures.

Point-Seven-five wrote:Are there any German members here who can comment on German regulations on power output for motorcycle engines in the early/mid 80's.  I seem to recall reading something about limits on engine output at the time.

That is correct, a limit of 100bhp but as far as I remember it was voluntary rather than mandated but it was to keep EU regulators away from imposing limits.

It's a shame that Inge is no longer with us. He'd know the answers. He knew more about K bikes than God.

From what I recall, the European K100 had cams that were a bit different to the K100 that was marketed in North America and Australia.
The difference is that the euro cams opened the inlet 20° earlier than the others. the later opening was done to make the engines meet the Californian emission regs. It did this by effectively allowing a bit less charge into the combustion chambers and so lowering the effective compression ratio and so reducing the combustion temperatures which in turn meant less oxides of nitrogen into the atmosphere.
Performance was not really affected much except for a slight reduction of low end torque and almost no measurable decrease in BHP.
The K75 was introduced about the same time that the K100 was introduced to the North American market and as far as I know the same cam profiles were used on both models but I don't know if the European market K75 ever had the same inlet cam profile as the Euro K100.
From what I can find the Australian K100 had the longer duration inlet cam up until the introduction of the K100 into North America then changed to the different profile to meet the Australian pollution regs.
I have never en-counted a different piston in use in the K75 than the higher dome 11:1 that is stated in the factory literature here in Australia.

Rick G wrote:
I have never en-counted a different piston in use in the K75 than the higher dome 11:1 that is stated in the factory literature here in Australia.

More I check this, more convinced I am that post 1986 K75 models have 10.5 : 1 compression. All the files I have checked in tech page I are according to this.

Also from tech page updates file:

" During 1986...

K75s went from 11.0 : 1 to 10.5 : 1 compression. Power went from 75@8500 to 70@8200, and torque went from 50@6750 to 48@6500
"

I read the K75s as plural form for all K75 models and not as the S-model
Do you have any BMW publication after -86 that states 11.0 : 1 compression for K75?

You say in tech pages what pages which publication. I can find nothing regarding this. Real OEM list 3 part numbers for K75 pistons but they refer to slight variations in diameter and nothing with regard to compression ratio.
I have factory brochures for all models that were available in North America to the end of production in 1996. All models.

I am not trying to pick an argument but where did you get this information.

Max Power	75 hp (55 KW) at 8500 rpm
Max Torque	68 Nm at 6750 rpm
Compression Ratio	11.0 : 1

flying finn & brick wrote:More I check this, more convinced I am that post 1986 K75 models have 10.5 : 1 compression.
K75s went from 11.0 : 1 to 10.5 : 1 compression. Power went from 75@8500 to 70@8200, and torque went from 50@6750 to 48@6500
Do you have any BMW publication after -86 that states 11.0 : 1 compression for K75?

The red text in the above quote is from Anton Largiader's useful site but is unfortunately a transposition of K100 data into a K75 reference in a section of his site. It was quoted in one post then corrected in another during earlier in this thread. Here is a screen shot of the entry at Largiader's site.


Attached is a specification table from a 1994 K75 Rider's Handbook indicating that the K75 is 11:1, as Rick G correctly asserts.

Rick G wrote:
I am not trying to pick an argument but where did you get this information.

Yes, my bad. I was posting in a bit of a hurry and started claiming things without providing proper background. So here it goes:

Wikipedia:
- claims both 11.0 and 10.5 to 1 ratios
- Source for 11.0 is year 1985 cycle world magazine
- Source for 10.5 is year 1995 US magazine called Motorcyclist print 2/1995. I didn't find this online so can't really evaluate.

K100 forums Kforum-Tech page:
- 1986 press release of new K75 states 11.0 : 1 on the very beginning of page 18. "https://www.kforum-tech.com/general/PDF/brochures/1986 Press Release.pdf"
- 1990 press release of the product range of BMW gives also 11.0 : 1 on page 38. "https://www.kforum-tech.com/general/PDF/brochures/1990 Press Release.pdf"
Also i checked some pages on BMW official site and all that I found was 11.0 for K75, making no separation with different production years. Most of the info was in German.

So far one might think this is all clear and easy with 11.0 to 1 comp ratio, but this is where it gets interesting:
- Sales brochure (year?) saying K75 and K75S have compression ratio of 10.5 to 1 on page 26
- An other sales announcement with specs from year 1989 presenting all K75 models with com ratio of 10.5 : 1. Page 11
- Year 1991 brochure gives also 10.5 : 1 on all K75 models from page 21 and on

Hypothesis I would like to make is that american model K75 bikes have lower compression 1986-> as the original poster was suggesting
- The source for 10.5 on wikipedia is american bike magazine post -86 era
- Product info papers that have stated 10.5 to 1 ratio has imperial units as main or at least as secondary units. I suppose these wouldn't exist on announcements for european audience.

Laitch wrote:The red text in the above quote is from Anton Largiader's useful site but is unfortunately a transposition of K100 data into a K75 reference in a section of his site. It was quoted in one post then corrected in another during earlier in this thread. Here is a screen shot of the entry at Largiader's site.

If I understand correctly, I doubt the theory of simply mixing K100 and K75 compression ratios. Does any K100 have 10.5 to 1 compression? Isn't it always 10.2 : 1 for older K100 models and 11.0 : 1 for K1 (and other 4v models)? Also the power (hp) and torque (lb⋅ft) figures given are 100% K75 specs.



I am not trying to prove anything right or wrong but this confused me quite a bit and I sure hope my K75 has 11 to 1 ratio . I almost felt betrayed when I stumbled upon the 10.5  to 1 figures when I have always taken the 11 for granted. What do you think?
Is the 10.5 : 1 an error on the publications or some American market spec for lowering NOX?
Is the 11 : 1 still lurking around from original K75 and just copied on and on without update on 1986?
And if the 11 -> 10.5 change is real how was it made? With thicker cylinder head gasket?

This is from the 1986 UK K-Bike brochure and it shows 10.5.

flying finn & brick wrote:Hypothesis I would like to make is that american model K75 bikes have lower compression 1986-> as the original poster was suggesting

I am not trying to prove anything right or wrong but this confused me quite a bit and I sure hope my K75 has 11 to 1 ratio .

Because the 1994 USA BMW Rider's Handbook published the 11:1 figure for the K75;
Because the 1988 BMW Service Manual compilation downloadable from this site (which claims to involve Australia, UK, Ireland, Canada and Germany} also published the 11:1 figure for the K75 in its engine specification table;
Because sales brochures can seem to dwell more on sales than accuracy;
Because engine specifications—and even vehicle model names—can vary from region to region;
Because multiple, putatively reliable sources are producing differing figures concerning this value;
Because there is nothing to prove right or wrong;

Hope would seem to be a suitable course to take, if dismantling the engine for measurement isn't in the program or choosing whichever figure to believe is unacceptable as a free will choice.

One of the answers to this debate must surely be the spare parts catalogue. 

Surely if different compression ratios prevailed then spare parts would reflect this? As in multiple types/shapes of pistons?

I am not aware of different ratios being available but maybe I am wrong. 

I am only aware of the 2v pistons being in two configurations, K100 10.2:1 and K75 11:1 but maybe someone can clarify all this.

92KK 84WW Olaf wrote:One of the answers to this debate must surely be the spare parts catalogue. 

Surely if different compression ratios prevailed then spare parts would reflect this? As in multiple types/shapes of pistons?

I am not aware of different ratios being available but maybe I am wrong. 

I am only aware of the 2v pistons being in two configurations, K100 10.2:1 and K75 11:1 but maybe someone can clarify all this.

just a quick note that luftmeister (earlier in this thread) has offered thinner head gaskets with claim "increases compression 1/2 points". So it has room for changes of that magnitude also there.

edit: Maybe standard spares represent one compression ratio but there has existed another variant with very minor changes (for reasons?). And maybe the minor variant didn't get own spares for the quirks it has. Wikipedia talks about US model made for EPA regulations that has slightly less power but it doesn't mention compression ratio nor it mentions source for info.

The press release from BMW AG Presse for the 1988MY bikes refer to the K75 having an 11:1 compression ratio with 75bhp. Valve timing and size is stated as being the same as the K100 2V, with the cylinder head "refined" to improve efficiency, no details given.

The BMW repair manual from 4/88 states the K75 has 11:1 compression and 75bhp, and the K100 90bhp with 10.2:1 compression ratio.

flying finn & brick wrote:Wikipedia talks about US model made for EPA regulations that has slightly less power but it doesn't mention compression ratio nor it mentions source for info.

The Wikipedia article might have mentioned it thusly—

The US market engine, specified to meet Environmental Protection Agency (EPA) requirements, produced 68 hp (51 kW); engines for all other markets produced 75 hp (56 kW).

Did the EU de-tune the K75? Maybe that was done in Germany, Switzerland and some other jurisdictions overseas but the inaccuracies of Wikipedia won't solve that riddle and so far, there is a dearth of compelling evidence that it ever occurred. In 1995 the EPA seemed not to have required the detuning of motorcycle engines to comply with any standard whatsoever. The USA didn't even start getting serious about motorcycle emissions until 2006, and even after that, many states don't inspect vehicles for any mechanical or emission reason, but manufacturers still need to have them to meet the demands of the EU market and its regulations.

Only the California Air Resources Board (CARB) required fuel tank fumes of classic Bricks to be routed into the crankcase for recycling into the combustion chamber so gasoline fumes wouldn't be emitted directly into the atmosphere. California was the only state out of 50 requiring this system; however, the size of the California market compelled BMW to rig all USA models with the modification. BMW eventually published a workaround for owners so it could be removed because it was reportedly causing performance problems. The fix was easy to accomplished but the system could be restored as easily prior to California vehicle inspection.

Maybe accepting or just pretending the Brick has the highest compression ratio and simply riding hell out of it is the solution to this conundrum. Wickipedia information has not been a particularly conclusive resource, at least not as conclusive as maybe twisting a well-tuned K75's throttle over a road through Järvi-Suomi.

Typing a lot about it and dwelling over it will not alter it.

Best to just forget about it and ride.

I checked my 1994 K75RT owner's manual.

Compression ratio - 10.5:1

??!!??

It's the large print edition, Point-Seven-five?

I was really surprised.  I had all along thought that the K75 compression ratio was 11:1 and that the pistons were interference with the valves.  Now I don't know what to believe.

It doesn't matter what we believe. Leave it to a Higher Power.

I am done with this thread.  I have no idea of what is correct anymore.