Background: engine been stripped and rebuilt. back on bike bike won't fire...worked through electrical side no fault found.... onto mechanical...

Just checked the compression.... Bearing in mind that the engine is cold my reading are...

Cyl 1 100 psi
Cyl 2 120 psi
Cyl 3 0 psi
Cyl 4 0 psi

not
tried to put any oil in the cylinders to see if it will increase them,
as a reading that low says something major... top end strip down now
see if my valves are Foobarred....

I have stripped the top end down (engine still on the frame) and the only thing i can see is as per the pic below. cylinder 4 is the right most
[img][/img]

As can be seen on one of the valves there is scoring, I am guessing this is where it's come into contact with the cylinder... suggesting it's not closing properly?
There is a similar mark on the same valve on Cylinder 1

The photo below is of the cylinders... which all look good...
[img][/img]

Any idea's or suggestions? It also pose's the question of should I pull the pistons out and do a visual check of the piston rings and strip the bottom end all the way down as well...

ok quick update... the Exhaust valve on Cyl 3 is bent.... how does that happen??
cyl 4 exhaust valve looks ok to me.... I have lapped it again and it appears to seat perfectly....

onto cyl 1 and 2 because cyl 1 has got a slight marking the same as cylinder 3 had...

The two ways valves usually get bent are;

1. Contact with the piston. Caused by either incorrect valve timing or a broken timing chain or belt. The latter usually wrecks the head.

2. Laying the cylinder head down on the gasket face with some valves open. It doesn't take much to slightly bend a valve if sideways pressure is applied to it.

Since you say that the engine has been rebuilt, then one would have to assume that either the valve timing was incorrect on re-assembly, or the head was laid down on the gasket face while it was off the engine.
If it was a valve timing issue then there should be marks on the pistons where they hit the valves.

Logic would also suggest that all 4 valves would show similar problems I would have thought, however the only marks are on the valve heads of cylinder 3 and 1 the valve in cylinder 3 being shot but the other is fine....

The pistons were spotless clean when I put it back together so no carbon build up to show any contact marks....

I cant find any problems with the top end side for cylinder 4 which also had 0 compression mind....

Twincarb, Is it possible the shop put in wrong valve shims. They would not have fired the engine, maybe not even done a compression test. The difference may have caused contact between the vlave and piston....I think. Best of luck.

KF

I am not the expert on this but I did see another post about timing chain wear, tensioner issues and possibilty of valve timing going slightly off.

I think looking at the photos I have done a few head jobs and love to to see everything nicely polished up, piston heads, valve cut outs, inside of the head and the valves themselves. If you havent done it I would have all the valves and springs out and clean out everything, check the valves for damage and being straight.

I havent checked on the seats/grinding in requirements but from what I see there were hardened seats used on later models to allow use of unleaded petrol. The other thing I have not checked is whether the pistons have a right/wrong way of being installed if the valves recesses are not the same on each side.

However if the engine was rebuilt none of this should be the case.

I wish I could point the finger at someone else! But alas it's my work!

The valve clearances were all identical when I put it back together as when I took it apart.

Still trying to work out what the problem is with Cylinder 4 I think it is going to be a bottom end strip next to check the rings...

The pistons fit one way.... well they will go in the "wrong" way but there are arrows that point in one direction so it's easy to get them right.... you can roughly see the arrows in the second photo at roughly the 9pm position and all point towards the cam chain...

Everything was spotless inside the head when it went back together all be it everything was given a light coating of oil.

The Valves can and should be reseated when they have been removed...

The biggist pain is that cause I have a bent valve I should/need to replace the valve stem as well hmmmmm

Do I need to remove the Output shaft before I remove the Crankshaft? is it possible with the engine still mounted on the bike?!

I would not be quite as quick to pull it all apart.

The low readings between two cylinders in car engines usually points to a leakage between two adjacent cylinders, probably at the narrow neck in the head gasket or the head just above it. The fact that the readings are so low suggests something 'big' and simple at the top end or holes in pistons which we clearly dont have.

I would have a relook at the head gasket itself too as I have seen different types of gasket materials cause problems here.

The bent valves have been commented on and are not difficult to resolve. Was the head checked for any cracks or skimmed?

The logic being that I would only see a reduced compression if the rings were shot?

The head hasn't been checked for flatness, I don't think replacing the valve stem is a job I want to do so will take it to my local engine rebuilder He will be able to check the head to ensure it's not warped...

The gasket certainly looked as if it had a good seal I used one from motobins which has got a blue silicon seal around the gasket which was compressed in an even way all the way around.

A lot of engines allow the removal of a big end cap and con rod/piston assembly if you remove the sump, without dismantling the engine. not sure if the K does. Do you have Clymer manual? I have a feeling one broken piston ring would not result in a zero reading but a low reading. 120psi gives you about 8:1 but for sure I would always get a second opinion as in try another gauge. Also, how are all the injectors/ injector seals? If you get the top end completely sorted and with good gasket I would like to feel it would solve your problem.

I am happy with the 120 reading as the engine was cold and I didn't open the throttle, in my mind the 2 good readings I got would be a fair chunk higher if the engine was hot and the throttle was wide open.

I have had a quick look at the Haynes manual and it would appear that the bottom end can be stripped from the position I am in now no need to remove the sump which is a blessing... I guess some purists would suggest stripping the bottom end down just to confirm the condition of the rings...

I read the Clymer for replacing the valve stems, and the thing that's put me off is the "special" tools for removing and then installing the valve guide....

As you say you may well have two good readings and I suspect the cause of the low readings may be simple. Bent valves being one and relatively simple for any engine shop to do for you.

Just looking at the picture of the head appears it h.as not torrqued down evenly
hence the blueing\blowback or may may be bowed (between 2 cylinders). the valve may not be bent but worn in a oval shape. I would be inclined to check the water passages prior to assembly to confirm a decent flow throughthe head that a blockage/air lock is not causing over heading insures remember to check the fan too else you will only have thermo syphon effect

hope this helps Tony

ps I ran OMO (washing powder )through my motor cleaned it like new but make sure you remove any residue else it suds up well

Put some petrol in the ports and see what happenns.
1 petrol stays--- Valves are OK
2 petrol runs past the valve---Valves are shagged i.e. bent from incorrect valve timing.
The #3 exhaust has hit the piston big time I can see that from the picture.
Remedy:- new valves.

um you didnt inadvertantly put the exhaust cam in the inlet cam place ? wonder what the valve timing would be like then ?

dry run perhaps ?

Rick,
I had completely forgotten about the simple technique of using petrol and seeing if it runs past the valves! Will be doing that shortly now.... am i right in thinking bent valve also means replace the valve stem?

Charlie,
I don't think it's possible to put the cams in the wrong place because everything is offset, it was one of the things that we had discussed in work, but kinda concluded that everything would be 180 degrees out... and if everything was still spot on but out it would have fired when swapping the low voltage i/p to the coils.... (i tried that!)

If the valve is bent the whole lot goes to the garbage the stems are all one part.
Because the valves are at about 45deg to the bore the cams would work out with one being 90 deg and the other 270 deg out.

sorry I meant guide not stem!

The valves usually bend just under the head and often there is a narrow part on the stem to let it happen there. The guides will probably be untouched but when the springs come off make sure they dont stick in the guide. If they are free then all will be OK.
I would advise to put new stem seals on when its apart.
And you are right they don't go in reversed.

Thanks Rick, that has made it a whole lot simpler then, there was no sticking of the spring in cyl 3 when I took it out.

With any luck I can order the parts today and they should be here tomorrow with any luck. Just got to rule out any other problems with the head and cyl 4.

If you are worried about a warp get an engine rebuilding shop to check it and/or do a surface grind but that blueing is from the coolant.

One thing to do before putting the head back on is do the shims before it makes it a heap easier and don't forget to use an antisieze on the bolt threads and under the head of the bolts

I seem to recall reading that you can put the head back on with the camshaft in place, but I am sure when I looked at it the head bolts were to close to the cams to get a proper grip on them!

Makes sense rechecking the shims on the bench mind.... I followed the Haynes manual last time and it just said to use a light coating of oil on the Head bolts i guess that anitsieze would be better mind

Right on with the adventure....

I have fitted the new valve and when cold all 4 cylinders are now showing 120 Psi which I am happy with being cold.

Engine starts and idles a treat

Onto the noise that I got from the rear end... essentially as soon as I increased the rev's I had a grinding noise and the engine stalled.

I have now stripped the bike back down... all the way with gearbox off, clutch off, bell housing off...

Quick peek inside and I can see where the problem is.... The Aux drive shaft is forced out onto the retainer plate and then it's coming to a stop.... It looks like I have everything in place that should be there but I can't see what the cause is.....

Any ideas as always welcome while I cook some dinner and look for info on here

BINGO.... sussed it... Just had a read of Albys Sprag clutch cleaning.... looks like I am missing the Shim which would stop the clutch moving forward.... Time to have a hunt in the garage/workbench....

Does anyone have the size of it??