My ex police K1100 LT recently suddenly lost power on the dual carriageway and seemed to be only running on 3 cylinders.  I managed to limp the bike home and park it up pending further investigation at a later date.  I have since discovered that there is zero compression on the number 3 cylinder (assuming cylinder 1 at the front of the engine).  Is this something that any of the knowledgeable members of this forum could advise me on and suggest possible ways forward ?

Thanks in anticipation   

krambo

My K1100 did the same thing when it broke the edge off an exhaust valve.
Have a feel round the top of the piston for a possible hole and if that is the case then it would be blowing a fair bit of smoke.
See if you can borrow an endescope that will go in the plug hole and get a look at the valves they could be bent or broken like mine was, you may also need to look in through the exhaust port at the back of the valves.
Check the valve clearances to see if any have opened up which would mean a bent valve.
It is possible that a head gasket has blown but if it was into the oil or water then that would show in the cylinder and if it were between the cylinders it would affect 2 cylinders.
Next alternative is to remove the head and have a look.
Feeding compressed air into the cylinder will tell you where it is leaking to as you will feel the air coming out the exhaust,  inlet tract oil or water system.

@RicK G wrote:My K1100 did the same thing when it broke the edge off an exhaust valve.
Have a feel round the top of the piston for a possible hole and if that is the case then it would be blowing a fair bit of smoke.
See if you can borrow an endescope that will go in the plug hole and get a look at the valves they could be bent or broken like mine was, you may also need to look in through the exhaust port at the back of the valves.
Check the valve clearances to see if any have opened up which would mean a bent valve.
It is possible that a head gasket has blown but if it was into the oil or water then that would show in the cylinder and if it were between the cylinders it would affect 2 cylinders.
Next alternative is to remove the head and have a look.
Feeding compressed air into the cylinder will tell you where it is leaking to as you will feel the air coming out the exhaust,  inlet tract oil or water system.

Thanks for the comments Rick.  There was no noticeable smoke coming from the exhaust/engine and no extraneous mechanical noises etc. when this happened.  Pretty certain that it isn't the head gasket as all other cylinders show good compression.  I reckon my only realistic option is to remove the head and take a look.  I have been trying to avoid having to do this as I have a very limited workspace in which to carry out strip down work under cover and cannot afford to get a pro to look at it just now.  Thanks again for your input  

If you do take the head off be careful to prevent the lifters from falling out on the exhaust side as they face down and slowly fall out of their bores and can get mixed up.

This happened me once on a car, ran all the checks, exhaust valve was the problem. Head off job but took the opportunity to do a few other jobs at the same time. On the K I would replace the exhaust studs. Curious though as to what happened, Ks are very reliable engines.

Thanks for all the comments/advice so far folks  

@RicK G wrote:
Feeding compressed air into the cylinder will tell you where it is leaking to as you will feel the air coming out the exhaust,  inlet tract oil or water system.

I'm starting to investigate the reason for being recovered home yesterday. It sounded similar to a cracked valve which I only experienced once before on a car and was hopeful it might be just a gammy header but having swopped the exhaust system this afternoon I can rule that out. 

How is the compressed air best fed into the Cyliner Rick G? I'd like to have a go before stripping the head.

Have you carried out a compression test Will????

No Bob....lacking the gadgetry!

@88 wrote:No Bob....lacking the gadgetry!

A Gunson one is about £25 in the UK, I am sure that they have them over there, an essential tool. Mine is about 20 years old now.

@BobT wrote:

@88 wrote:No Bob....lacking the gadgetry!

A Gunson one is about £25 in the UK, I am sure that they have them over there, an essential tool. Mine is about 20 years old now.

My tool is the same age as me.

@88 wrote:

@RicK G wrote:
Feeding compressed air into the cylinder will tell you where it is leaking to as you will feel the air coming out the exhaust,  inlet tract oil or water system.

I'm starting to investigate the reason for being recovered home yesterday. It sounded similar to a cracked valve which I only experienced once before on a car and was hopeful it might be just a gammy header but having swopped the exhaust system this afternoon I can rule that out. 

How is the compressed air best fed into the Cyliner Rick G? I'd like to have a go before stripping the head.

I made a compressed air adapter from a busted spark plug by breaking the porcelain out and welding an air fitting to it.

@92KK 84WW Olaf wrote:

@BobT wrote:

@88 wrote:No Bob....lacking the gadgetry!

A Gunson one is about £25 in the UK, I am sure that they have them over there, an essential tool. Mine is about 20 years old now.

My tool is the same age as me.

If it is that old Olaf, it is probably a tool for getting stones out of horses hooves as motorbikes weren't invented when you were born!  Why is it that so many school kids had a penknife with a tool for the horses when we never went near horses?

@RicK G wrote:

@88 wrote:

@RicK G wrote:
Feeding compressed air into the cylinder will tell you where it is leaking to as you will feel the air coming out the exhaust,  inlet tract oil or water system.

How is the compressed air best fed into the Cyliner Rick G? I'd like to have a go before stripping the head.

I made a compressed air adapter from a busted spark plug by breaking the porcelain out and welding an air fitting to it.

Or get you one like this from the local automotive tool shop (or the net).

Aside from motorcycles I also work on airplanes, the kind with reciprocating engines.  To test compression the propeller is rotated (with the top spark plugs out) until you get to TDC.  At this point you install a spark plug adapter and connect the differential compression tester.  This gizmo has two pressure gauges on either side of an .040 orifice, you slowly apply pressure to the tester (while holding the prop) and adjust the valve for 80 PSI on the hose side, then observe the gauge on the cylinder side, if you have a good one the reading on the gauge will be within 10% of the hose side.

I really don't see how useful a single gauge "differential" compression tester intended for advanced shade tree mechanics are going to be of too much help.

Cars/bikes, the idea here is to crank the engine while holding the throttle wide open.  The tester is a simple gauge with a memory that reads the maximum pressure developed while cranking the engine around a few times until the highest pressure is noted and it's not going any higher. (*gasp*) Some gauges have a rubber cone you hold in the spark plug hole with your thumb, not so good, the better ones have a hose and a spark plug adapter, better.  Compare with the manufacturers specification, if it's above the magic number you are good to go.  If you do all four (or more) of them and the readings differ from jug to jug this shows a problem.On a healthy engine the differential from cylinder to cylinder should all be within 10%  On a high mileage engine they can be as high as 30% and it will still run okay.  Anything more than that not so good.

A new way is to use a special tool that is a current clamp on the starter motor lead plus a sensor on the #1 spark plug, pull all the plug wires, you don't want the engine to start. As the engine cranks various amounts of juice will be drawn by the motor depending on where the engine is in the cycle (compression takes the most) and comparing the graph.  With a good 4 cyl. engine you'll see something like 210 - 205 -210 - 75 amps.  The last cylinder in the firing order only drew 75 amps, showing that this cylinder was exhibiting low compression because the starter didn't need as much current to push through compression on that one .  The first time I saw this method used was with my old Ford pickup that had developed a poor idle, This was the Ford approved method to testing.  Sure enough I had a leaking valve that didn't show up with my conventional shade tree methods.

If you know what you are listening for you can spot a low jug as the engine is cranking.  Very handy junk yard technique when selecting an engine that's on the ground.

*Now for something you'll really like!*

Low compression on your K-Bike, first pull the valve cover and check the valve lash, if you have developed a valve issue you'll likely find no valve clearance (burned/broken valve), or if the spring is broken it will be vary obvious as there will be huge clearance. On burned valve, if the valve lash is allowed to degrade to "zero" the valve will be held open more and more, until the flame front whooshes (that's a technical term) past the valve head causing it to become severely overheated and melt.  On engines of yesteryear it was not uncommon to see erosion on the valve seat that allows leakage resulting in eventual Barbeqvalve syndrome.

So, that's what I know...

Da Bee - AKA John.

Did this make any sense??

@Inge K. wrote:

@RicK G wrote:

@88 wrote:

How is the compressed air best fed into the Cyliner Rick G? I'd like to have a go before stripping the head.

I made a compressed air adapter from a busted spark plug by breaking the porcelain out and welding an air fitting to it.

Or get you one like this from the local automotive tool shop (or the net).

Mine is cheaper

That makes sense Bee/John. Interesting about current draw. 

I think I'll try the Rick G approach with a welder and spark plug rather than buy a tool I may only use once.

Hi Will

I have a compression tester if you want to borrow it.

[quote="RicK G"]

@88 wrote:

@RicK G wrote:


How is the compressed air best fed into the Cylinder Rick G? I'd like to have a go before stripping the head.

I made a compressed air adapter from a busted spark plug by breaking the porcelain out and welding an air fitting to it.

I did the same and if you can rotate the crankshaft and the noise of air escaping does not stop you have a mechanical problem such as valve burnt out , hole in piston,

I always hope that the exhaust/inlet valve adjustment is way off...and fixable.

good luck

Just remove the valve cover, you'll most likely find your issue there.  Since the engine runs we know it's not an intake valve, Check them out from there, you'll find it.
If you have a holey piston the engine would be belching tons of smoke.

If I were a betting man I'll guess you either have a blown out head gasket or burned valve or broken spring.

Hows the coolant level look?  If it's low or gone this would indicate a head gasket.

Have fun.