BMW K bikes (Bricks)

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DadofHedgehog

DadofHedgehog
Silver member
Silver member
Folks,

I happen to have the cylinder head off for some work... my 1995 K75 has the Torx T50 cylinder head bolts.  They came out this morning without problems.  All their threads look to be in good condition under visual inspection.

My K75 has fewer than 14,000 miles.  I am the 3d owner, and more than half of its miles are under my ownership.

So, question - should I re-use these bolts, or pop for new ones?  In car engine rebuilds, the sage old-timer advice is to "always use new cylinder head bolts".  I have several weeks before I have to decide...

Note: there is nothing mechanically wrong with the cylinder head... this is a horsepower improvement vanity project.

Comments are welcome.

Thanks!


__________________________________________________
PRESENT:
1995 K75T.  I am the 3d owner.  Bought it in June 2019 with 6,242 miles on the odo.
1991 K100RS 4-valve attached to a 1990 Flexit sidecar. I am at least the 3d owner. Bought with 21,00+ miles on bike's odo.

PAST:
old (indeterminate age) Ural + sidecar
1997 Buell S3T Thunderbolt
1982 BMW R100CS
1974 Kawasaki KZ400
1970 Suzuki Titan
    

2Back to top Go down   K75 cylinder head bolts - buy new or re-use? Empty Head bolts Wed May 05, 2021 12:00 am

daveyson

daveyson
Life time member
Life time member
I would use the original bolts. 

I don't think the BMW workshop manual says to replace with new, but can't count on my memory.

Assuming they're all the same length, I would replace any that are 0.3mm or longer than the shortest one. Anyway that's what I used to do with my cars, back in the days.

Even if you do have to go back in, it's not as hard as with a lot of other makes, but I don't think you will have to.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

Dai

Dai
Life time member
Life time member
Re-use. Don't have a manual to hand but in general, you should be doing a torque check after around 500 miles anyway. I have never, on any bike I've owned, had any problems with re-using cylinder head bolts.


__________________________________________________
1983 K100 upgraded to K100RS spec, 1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

Laitch

Laitch
Life time member
Life time member
@DadofHedgehog wrote: this is a horsepower improvement vanity project.
I think brand new head bolts would fit right into a project like this. You could paste a sticker, Head Bolts by Bling Brothers on the fuel tank or fairings.  Smile

What's the project?


__________________________________________________
1995 K75 81,000 miles
K75 cylinder head bolts - buy new or re-use? Usa-lo10
    

DadofHedgehog

DadofHedgehog
Silver member
Silver member
@Laitch wrote:
@DadofHedgehog wrote: this is a horsepower improvement vanity project.
I think brand new head bolts would fit right into a project like this. You could paste a sticker, Head Bolts by Bling Brothers on the fuel tank or fairings.  Smile

What's the project?
Haha - got a sticker? ;-)

Power project has 3 steps.
- K1100 throttle bodies (done).
- the new throttle bodies, half-shafted (done)
- gasflowing the cylinder head by BSK Speedworks (in transit).


__________________________________________________
PRESENT:
1995 K75T.  I am the 3d owner.  Bought it in June 2019 with 6,242 miles on the odo.
1991 K100RS 4-valve attached to a 1990 Flexit sidecar. I am at least the 3d owner. Bought with 21,00+ miles on bike's odo.

PAST:
old (indeterminate age) Ural + sidecar
1997 Buell S3T Thunderbolt
1982 BMW R100CS
1974 Kawasaki KZ400
1970 Suzuki Titan
    

DadofHedgehog

DadofHedgehog
Silver member
Silver member
@daveyson wrote:I would use the original bolts. 

I don't think the BMW workshop manual says to replace with new, but can't count on my memory.

Assuming they're all the same length, I would replace any that are 0.3mm or longer than the shortest one. Anyway that's what I used to do with my cars, back in the days.

Even if you do have to go back in, it's not as hard as with a lot of other makes, but I don't think you will have to.

Good - thanks!


__________________________________________________
PRESENT:
1995 K75T.  I am the 3d owner.  Bought it in June 2019 with 6,242 miles on the odo.
1991 K100RS 4-valve attached to a 1990 Flexit sidecar. I am at least the 3d owner. Bought with 21,00+ miles on bike's odo.

PAST:
old (indeterminate age) Ural + sidecar
1997 Buell S3T Thunderbolt
1982 BMW R100CS
1974 Kawasaki KZ400
1970 Suzuki Titan
    

moriarti

moriarti
Life time member
Life time member
Just a point, i was taught to lube all head bolts clean engine oil is fine, Modern day pastes are available, this method improves toque accuracy, so i was told when i was a lad.


__________________________________________________
1984 k100 rs red/black VIN  0004449
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Lubricating with anti-seize would have prevented the breaking of one of the head bolts on my '92 K100RS.

A tiny bit of water coming down off the engine below the throttle position sensor was able to penetrate the head gasket and get into the threads of the head bolt. The resulting corrosion together with the torque on the bolt essentially welded the threads into the engine block.

Drilling a hardened screw out of an aluminum block sucks.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Arlina

Arlina
Moderator
Moderator
They are stretch bolts, wich adapts to the life in the head as long as it stays there.
BMW say use new bolts.

However, besides me, I know some people who reuse the old bolts, and haven't face a problem.
Saved some money to buy a beer afterwards to celebrate Smile


__________________________________________________
K75 cylinder head bolts - buy new or re-use? Eu-log10  K1100RS/LT - R1200RT - R1100RS (RIP) - Cagiva SST 350 Ala Verde - K75LT project - K75 Schurgers - K75S
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Arlina, I agree. At $16.56US a pop you can bet that I'll reuse the old bolts. My '92 16 valve RS is still running nicely on it's old bolts 4 years after I put them back in after a head job.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

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