I searched and read a few of them. I agree it doesn't look any worse than yours. Motors ready to lift out. There is something weird going on in there.
Going to pop the motor out in a few minuets. It needs to be looked into.
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Compression puzzle
- Thread starter GLJ
- Start date
Going to pop the motor out in a few minuets. It needs to be looked into.
It's out. Not sure if it's break time or quitting time. Happy hour may be early today.
I hope by this time tomorrow I/we have it figured out.
I hope by this time tomorrow I/we have it figured out.
As I'm sure you know, applying the cam chain tensioner will roll the cam backwards as it takes up the slack. That's why 2M's is like that, he's got an old, fairly stretched chain in there. But your chain was new so I wouldn't expect to see that much stretch in 6K miles. Unless maybe you had it set too tight?
Interesting engine stand. Show us some more pics of that.
Interesting engine stand. Show us some more pics of that.
That Greg doesn’t mess around! 
Had the cam chain adjusted normally for a 256 engine. Got the chain on E-Bay, NOS came in Yamaha packaging.
I'm going to blame it on Wally World oil, that stuff caused me a clutch problem.
Occasionally I pick up parts bikes. I try to give the frames away but with no titles I don't get any takers. So I turn the frames into engine stands. This one is from a 75. One thing I like about them is with the curve you can roll the engine on it's back easily. I've made 3 so far. Better than scrapping them.
I'm going to blame it on Wally World oil, that stuff caused me a clutch problem.
Occasionally I pick up parts bikes. I try to give the frames away but with no titles I don't get any takers. So I turn the frames into engine stands. This one is from a 75. One thing I like about them is with the curve you can roll the engine on it's back easily. I've made 3 so far. Better than scrapping them.
I think I have it figured out! Even how I was able to ride it into the shop and then have the compression check at 20lbs 10 days later.
I was not 100% correct in assuming the cam was off by a tooth.
More later.
I was not 100% correct in assuming the cam was off by a tooth.
More later.
This may be a little long and hopefully not too convoluted.
Took the rocker cover off and as I expected cam is late. No big surprise. I was convinced it would be a tooth off. It's not. Hard to see in the pic, it's not a full tooth off. I removed the cam chain adjuster so the can has all it's slack. Then set crank to TDC. Moving the cam each direction by hand until the slack is gone backs the mark of equal a amount from where it should be.
Looked at rockers. They show a bit of wear, I can feel that slight flat spot with my finger. I do think they are a contributing factor but no smoking gun. For all 4 or even 2 to wear at the same time to the point of causing a severe compression drop is a stretch.
The discoloration on the rocker is a reflection.
Looked at the cam, no flat spots on it. Looks OK. Camera makes it loose worse than my eyes.
Thinking cap and more coffee time.
I'm convinced that late cam timing is causing the problem. Increasing the valve clearance from 3 to 6 nd getting back to the compression I had before the Ozark to me proves that. I'm thinking the combination of the chain stretch and the wear on the rockers is the cause. New cam chain and better rockers it should be good to go.
What kept bugging me is how did all this happen at once on a engine that had just been sitting. I then had a eureka moment where it all came together, even the cause of this mess.
Think about it .003 increase in valve clearance increased the compression from 25 to 125. I don't think .003 at the valve tip can be that much in relation to cam timing. If someone wants to figure it out go ahead. I think I would get a headache trying to. Anyway the cam chain stretch must have been right at the tipping point of causing this. What changed to tip over the apple cart. When I said in the beginning of this thread all all I had done to it was clean and service it. Service had consisted of cleaning carbs and oil change, neither should cause this. Well I did one other thing which could. Didn't mention it because I didn't think it was relevant. I noticed on the trip back my base gasket was seeping a little oil. What is the recommended thing to do with a seeping base gasket. Re-torque the head. I had done it at 500 smiles, figured it was due. I'm thinking re-torquing compressed the head and base gasket just enough to tip over the apple cart. Any more compression of the gaskets is the same as chain stretching. I know the amount of chain stretch would be half of compression.
My plan is to replace the cam chain, base gasket and rockers. I have a used set of rockers that look great.
Now what caused the cam chain to stretch, rockers to wear and base gasket to leak plus an odd clutch problem. One of two things. One could be my brothers spirit, would not put that past him. The other is oil. Last summer I switched from all VR1 to 1500ML of 20W50 Wally World oil with the rest VR1, then adding VR1 as needed for make up. I'm going to blame Wally World. Switching back to 100% VR1 fixed the clutch issue.
That's my story and I'm sticking to it. Unless someone shoots holes in it.
I did put the adjuster back in and set it. From the face of lock nut to the end of the adjuster measured 10.53 mm. Just thought I would throw this out there. This is a 256 adjuster. Be interesting to hear from other guys with them what theirs measure.
Took the rocker cover off and as I expected cam is late. No big surprise. I was convinced it would be a tooth off. It's not. Hard to see in the pic, it's not a full tooth off. I removed the cam chain adjuster so the can has all it's slack. Then set crank to TDC. Moving the cam each direction by hand until the slack is gone backs the mark of equal a amount from where it should be.
Looked at rockers. They show a bit of wear, I can feel that slight flat spot with my finger. I do think they are a contributing factor but no smoking gun. For all 4 or even 2 to wear at the same time to the point of causing a severe compression drop is a stretch.
The discoloration on the rocker is a reflection.
Looked at the cam, no flat spots on it. Looks OK. Camera makes it loose worse than my eyes.
Thinking cap and more coffee time.
I'm convinced that late cam timing is causing the problem. Increasing the valve clearance from 3 to 6 nd getting back to the compression I had before the Ozark to me proves that. I'm thinking the combination of the chain stretch and the wear on the rockers is the cause. New cam chain and better rockers it should be good to go.
What kept bugging me is how did all this happen at once on a engine that had just been sitting. I then had a eureka moment where it all came together, even the cause of this mess.
Think about it .003 increase in valve clearance increased the compression from 25 to 125. I don't think .003 at the valve tip can be that much in relation to cam timing. If someone wants to figure it out go ahead. I think I would get a headache trying to. Anyway the cam chain stretch must have been right at the tipping point of causing this. What changed to tip over the apple cart. When I said in the beginning of this thread all all I had done to it was clean and service it. Service had consisted of cleaning carbs and oil change, neither should cause this. Well I did one other thing which could. Didn't mention it because I didn't think it was relevant. I noticed on the trip back my base gasket was seeping a little oil. What is the recommended thing to do with a seeping base gasket. Re-torque the head. I had done it at 500 smiles, figured it was due. I'm thinking re-torquing compressed the head and base gasket just enough to tip over the apple cart. Any more compression of the gaskets is the same as chain stretching. I know the amount of chain stretch would be half of compression.
My plan is to replace the cam chain, base gasket and rockers. I have a used set of rockers that look great.
Now what caused the cam chain to stretch, rockers to wear and base gasket to leak plus an odd clutch problem. One of two things. One could be my brothers spirit, would not put that past him. The other is oil. Last summer I switched from all VR1 to 1500ML of 20W50 Wally World oil with the rest VR1, then adding VR1 as needed for make up. I'm going to blame Wally World. Switching back to 100% VR1 fixed the clutch issue.
That's my story and I'm sticking to it. Unless someone shoots holes in it.
I did put the adjuster back in and set it. From the face of lock nut to the end of the adjuster measured 10.53 mm. Just thought I would throw this out there. This is a 256 adjuster. Be interesting to hear from other guys with them what theirs measure.
Pretty much every one of these I've torn down has had a pretty badly stretched cam chain. They've all been D.I.D. chains and the motors usually had mileage in the 20 to 25K range. I don't know, maybe the chains Yamaha used back then weren't that good ..... and that's what you put in yours, one of those old chains. I would recommend using a Tsubaki chain this time, they're supposed to be a little stronger and better .....
https://www.mikesxs.net/yamaha-xs65...-x-102-oem-94510-01102-00-94590-02102-00.html
https://www.mikesxs.net/yamaha-xs65...-x-102-oem-94510-01102-00-94590-02102-00.html
Not sure if this is well thought through ..but I put it here as a theory
Engine ran fine
Standing still drops compression a lot ( tested on kick starter ??? )
Chain worn ? Short time and there is a spring and it can move a bit in and out
Bottom gasket perhaps
If I remember right the cam chain tension mechanism is there to compensate for thermal expansion.
Cold has another cc between center crank and center cam shaft .
Than when hot.
So assuming the cam chain tight when hot. No slack in front the adjuster in position " out "
When it gets cold the cc decreases . adjuster in position " in "
Viewing the engine from the left side with cold engine there is shorter distance .. And a slack in the chain should be there if not the tensioner spring adjusted .. But to adjust a slack at the front part of the chain means that the cam turns a little relative to the crank sprocket
Removing the slack in the pulling part of the chain
I'm convinced that late cam timing is causing the problem
With a loose lash fine but with a tight possibly turned a little and Off opening at the wrong time
Engine ran fine
Standing still drops compression a lot ( tested on kick starter ??? )
Chain worn ? Short time and there is a spring and it can move a bit in and out
Bottom gasket perhaps
If I remember right the cam chain tension mechanism is there to compensate for thermal expansion.
Cold has another cc between center crank and center cam shaft .
Than when hot.
So assuming the cam chain tight when hot. No slack in front the adjuster in position " out "
When it gets cold the cc decreases . adjuster in position " in "
Viewing the engine from the left side with cold engine there is shorter distance .. And a slack in the chain should be there if not the tensioner spring adjusted .. But to adjust a slack at the front part of the chain means that the cam turns a little relative to the crank sprocket
Removing the slack in the pulling part of the chain
I'm convinced that late cam timing is causing the problem
With a loose lash fine but with a tight possibly turned a little and Off opening at the wrong time
I'm not sure but I thought the OEM chain was Tsubaki. I could be wrong. The replacement chain I'm going to put in will be a newer Tsbubaki from Mikes.
Have you torn down 256 engines, they were a little different?
How do the pistons, bores look?
Sump'ns still nagging me that you don't have the whole story sussed out yet.
Sump'ns still nagging me that you don't have the whole story sussed out yet.
Tomorrow I'm going to pull the head and cylinders. Not to worried about the cylinder bores,pistons,rings,ect because they pumped 145 psi with the adjusters loose. What are you thinking might be be wrong? May help if was looking for another cause.
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I've got that nag too. Damned if I know what else though...
Me too a little. Too many times I've thought I've had everything figured out and then the other shoe dropped.
Like I said for now that's my story (or premise) and sticking to it.
Well at least until proven wrong.
Well at least until proven wrong.
just looking for clues, some sort of oil failure possible?
gas in crank, oil out of spec? clutching at straws.
gas in crank, oil out of spec? clutching at straws.
GLJ, excellent pics of your worn rocker pads. Downloaded copies for my files.
A few thoughts. You may already know about these.
With those grooves in the rocker pads, adjusting lash to minimums will have the edges of the grooves engaging the cam's entry ramps much earlier/later than normal by a few degrees, which is double that when observed at the crank.
The camshaft is likely toast. Have a look at @SomervilleXS650 thread refresh, covering a similar worn rocker/pad scenario. Starting at page 9.
http://www.xs650.com/threads/1974-tx650a-restoration-project.57476/page-9#post-685701
You may have a top-end lubrication issue.
May want to explore your oil pump.
http://www.xs650.com/threads/oil-pump-drive.49405/
http://www.xs650.com/threads/a-collection-of-xsjohns-mods.2426/#post-26637
To monitor this kinda thing, I run a top-end oil pressure gauge.
http://www.xs650.com/threads/xs650-top-end-oil-pressure-gauge.45317/
And, run a high-volume oil pump. The top-end runs cooler and quieter.
http://www.xs650.com/threads/hp-oil-pump-from-mikes.40991/
My other XS1B also experienced stretched camchain in short periods, around 6,000 miles.
My suspicion on the short life of the 256 camchains is in the design of the tensioner system, using a sprocket (a single-point load) versus the later 447 gently curved slippers (a lower, distributed load).
The "single-point" loading of the tensioner sprocket will induce much higher chain tension as compared to the "gentle arch". Imagine laying in a hammock, versus standing in it.
While you're at it, wouldn't hurt to polish the edges of the camchain plates to reduce tensioner wear.
More XS2 camchain tensioner pics in Mailman's restoration thread.
Post #726.
http://www.xs650.com/threads/mailman’s-xs2-a-full-on-restoration.51520/page-37#post-552926
Post #818.
http://www.xs650.com/threads/mailman’s-xs2-a-full-on-restoration.51520/page-41#post-553787
Mailman's albums.
http://www.xs650.com/media/albums/1972-xs2-engine-tear-down-reference-photos.3058/
http://www.xs650.com/media/albums/mysterious-cam-chain-stopper-xs2.3061/
A few thoughts. You may already know about these.
With those grooves in the rocker pads, adjusting lash to minimums will have the edges of the grooves engaging the cam's entry ramps much earlier/later than normal by a few degrees, which is double that when observed at the crank.
The camshaft is likely toast. Have a look at @SomervilleXS650 thread refresh, covering a similar worn rocker/pad scenario. Starting at page 9.
http://www.xs650.com/threads/1974-tx650a-restoration-project.57476/page-9#post-685701
You may have a top-end lubrication issue.
May want to explore your oil pump.
http://www.xs650.com/threads/oil-pump-drive.49405/
http://www.xs650.com/threads/a-collection-of-xsjohns-mods.2426/#post-26637
To monitor this kinda thing, I run a top-end oil pressure gauge.
http://www.xs650.com/threads/xs650-top-end-oil-pressure-gauge.45317/
And, run a high-volume oil pump. The top-end runs cooler and quieter.
http://www.xs650.com/threads/hp-oil-pump-from-mikes.40991/
My other XS1B also experienced stretched camchain in short periods, around 6,000 miles.
My suspicion on the short life of the 256 camchains is in the design of the tensioner system, using a sprocket (a single-point load) versus the later 447 gently curved slippers (a lower, distributed load).
The "single-point" loading of the tensioner sprocket will induce much higher chain tension as compared to the "gentle arch". Imagine laying in a hammock, versus standing in it.
While you're at it, wouldn't hurt to polish the edges of the camchain plates to reduce tensioner wear.
More XS2 camchain tensioner pics in Mailman's restoration thread.
Post #726.
http://www.xs650.com/threads/mailman’s-xs2-a-full-on-restoration.51520/page-37#post-552926
Post #818.
http://www.xs650.com/threads/mailman’s-xs2-a-full-on-restoration.51520/page-41#post-553787
Mailman's albums.
http://www.xs650.com/media/albums/1972-xs2-engine-tear-down-reference-photos.3058/
http://www.xs650.com/media/albums/mysterious-cam-chain-stopper-xs2.3061/
Out of curiosity... were you adding ZDDP to the oil?
No, I actually never tore into a 256 motor. I have one but it's still together. In all the 447's I've been into, I found D.I.D. chains.
And when I do the cam timing, this is the notch I usually go by, not that dot on the other side of the sprocket. You want it pointing straight up .....
And when I do the cam timing, this is the notch I usually go by, not that dot on the other side of the sprocket. You want it pointing straight up .....
