Minimum compression on a R65 head

[Adamastor]

125 is within acceptable range, though I would think that if one cylinder has 20 PSI better compression readings it is still going to be doing a bit more work, and the engine won't be quite as smooth as it could be.

So what did you set the valve lash clearance to be on the low cylinder to bring up the number?

I'd ride it as others have suggested, and keep an eye out for oil consumption.   Over the winter when we cannot ride over here, I'd plan to do the rings, and check over the valve seats on both sides, too - if the heads are coming off, may as well get the valves done IF they are in need of it.

I had the intake valve clearance a bit too narrow (I had seen that these later airheads could use 0.05 mm on intake, so I had it between 0.05 and 0.1mm)). Now I have 0.10mm..

I ordered the kit of new rings from motobins and since I wont be running (waiting for dyna coil) I will do the ring job

It wont hurt to have new rings, right? Besides that my rocker arm rubber inserts were leaking oil, so this will be usefull...

[Adamastor]

The other way to see if it is the rings leaking or the valves leaking is to put a small amount of engine oil down the sparkplug hole before doing the compression test.
If it is the rings that are worn, this should raise the compression, if it is a valve problem the compression will read the same as it was without the oil.

Hi!

I have just done this test with a bit of oil down the sparkplug hole, and got an impressive 150 psi compression. I am glad I ordered the new rings already ehehe

thanks for the tips!

[Adamastor]

Hi there!

I am a bit disappointed since I have just changed the rings on the low compression cylinder, and after torquing everything up and cranking the engine I got the same compression I had before

What could be wrong then? There were no scratches on the cylinder neither on the piston (on its travel) only the top (combustion chamber) had some marks... I also de-carbonized the chamber..

I am a bit clueless and tired (took me 3 hours to do this job on only one cylinder...)

I need you airheads detectives opinion on my "mystery"

[Bob_Roller]

About the only other possibilities after ruling out the rings and cylinder, are intake or exhaust valves not sealing on their seats, or cylinder head gasket leak .

You could try some soapy water on the cylinder head/cylinder gasket joint, and then rotate the starter, and see if you can see any bubbles, or foam develop .

[Adamastor]

I got all new gaskets and also liquid sealant on the cylinder to engine surface. I noticed there wasn't the big O-ring of the cylinder base. Now I have one there...
Apart from the rings, what else could be wrong with the cylinder/piston?

Regards,

Sergio

[Adamastor]

And one more thing, is there an easy way to clean the valves and their seats? I cleaned the chamber but the valves were closed...

[Bob_Roller]

I wouldn't think the cylinder is the problem, as it should be a 'nikasil' cylinder, kind of like a chrome plated cylinder, unless the plating is missing in spots, I can't see it being worn .

For the piston to be worn that much, I think it would be obvious by just looking at it .

[Adamastor]

Hmm one more thing I observed... I tested the compression with no carburettor and no exhaust tubes, and I saw on the outake kind of a cloud on each cycle... I thought that it could be remains of oil or dust on the exhaust tube, but maybe it should be only clean air coming out, right?

[Adamastor]

I went to the garage to look back to the cylinder... there are some imperfections near the edge, can this be the culprit?

Hi-resolution galery: http://img198.imageshack.us/gal.php?g=igp9867.jpg

The bad spot:



The piston head also has some marks, but on the top, not on the lateral walls...

Please give me your expert opinion... Is this the culprit for not having good compression?

[Bob_Roller]

I think you have found your problem .

I can't quite tell form the photo, but it appears that there may have been a valve issue on this cylinder .

[Adamastor]

But if you look to the above photo, you see that most the scratches end before the "reach" of the first piston ring... would they still be noticeable?

If so, what would be the solution? Rebore + new piston? Is it easy to get new sized pistons? Rebore will kill the nikasil finish?

So many questions... I know I am a pain in the $%# :p Sorry!

[Bob_Roller]

How does the cylinder head look ?

This has the appearance of something got loose and banged around the cylinder (like a valve head), not a good thing .

I don't think you can bore out a nikasil cylinder, maybe someone else knows for sure, and can comment .

[Adamastor]

Hmmm what is the cylinder head? (sorry) Apart from the scratches you can see on that photo, the rest seems ok, no scratches or marks...

One more question: Can you use a 1980 cylinder with this engine / head?

[Adamastor]

Oh, the head is where the valves are (lol)... I took a picture:

[Lucky_Lou]

I think a rebore is required haveing seen the cylinder and fit the aproprate oversize rings.
Lou