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Compression puzzle
- Thread starter GLJ
- Start date
I'll post better pics of it when I get it out.
What RPM do you upshift at?
Between 4000 and 5000
If things can go from bad to worse they will. More on that later
2M has concerns about the condition of the cam. To me it looks good. In the pics it doesn't look the greatest. In person it looks a lot better. No discoloration from heat. Surface nice and smooth everywhere. Can't feel any groves or ridges at all.
Since the base gasket was seeping a little decided to change it since I'm in this deep. Removed head, cylinder and pistons. Then started looking at things. Wrist pins are toast not good. If it looks like it's worn in the center it's because it is. Neither pin shows a heat discoloration. Both slid right out and felt nice and oily. Not good.
Hated to but figured I had better look at the rods. Both look the same. Shiny top and bottom 1/4s, sides coppery looking. To me they look worn out.
What do you guys think?
Never had these problems until I used Wall World oil in it.
2M has concerns about the condition of the cam. To me it looks good. In the pics it doesn't look the greatest. In person it looks a lot better. No discoloration from heat. Surface nice and smooth everywhere. Can't feel any groves or ridges at all.
Since the base gasket was seeping a little decided to change it since I'm in this deep. Removed head, cylinder and pistons. Then started looking at things. Wrist pins are toast not good. If it looks like it's worn in the center it's because it is. Neither pin shows a heat discoloration. Both slid right out and felt nice and oily. Not good.
Hated to but figured I had better look at the rods. Both look the same. Shiny top and bottom 1/4s, sides coppery looking. To me they look worn out.
What do you guys think?
Never had these problems until I used Wall World oil in it.
Attachments
I think it more so when the XS1s used a needle bearing.
Re the little end: I've always gone by the rule that if the copper cladding is worn through, the rod's bad. Having said that, the copper in my SG was just starting to wear through and I used 'em. Yours are well past that. As many miles as you put on that bike, I'd replace 'em.
Agree with 2M.... I'd replace that cam.
Agree with 2M.... I'd replace that cam.
I seem to recall there's rods for the 256 motors that don't use the needles? 
My thoughts.
Yeah well neither the small end nor the cam looks "Mint " so to speak .
The small end can even be at the latter stages of life.
But again what can look mint on a 50 year old motorcycle.?
Thinking out loud here . The cam a bit worn . Rockers a bit sloppy .at all ends.
Cam chain taken a beating ..moving the synchronization a bit between crank and cam .
Valve lash a the tight end .. Perhaps not set at the perfect spot
All in all a solution appears to be there in having a little more valve play.
Nothing blue and nothing really pitted can be seen or metal transfer from surfaces
No problems with the ride. Recently.
Option 1 Tear it down .. in my view to soon and costly ..
All in all this is a running bike with a minor problem after standstill
Option 2 Accept it as it is .. I would do something like look for a better cam ..replace wrist pins
check valve seats if not certain compression tests are " perfect "
Check lubrication and pump Using better oils and change more often.
.And perhaps forgot something here .. And ride some more.
Me coming from "C*ap " bikes are used to do such compromises. I do know others have other preferences and don't want it other than perfect.
But if aiming having a mint 50 year old bike ..And ride with it .. is costly and time consuming and unless being a competent mechanic
The risk is there having no bike at all.
All in all a solution appears to be there in having a little more valve play.
Here is summer coming up A tear down would mean no riding Less than perfect..
Once you start down the path.
Find a good late model motor and transplant the internals if you want to keep it numbers matching.
OR just throw a late model in the chassis go back to riding, and worry about fix'n the "correct motor" as time n funds allow.
Find a good late model motor and transplant the internals if you want to keep it numbers matching.
OR just throw a late model in the chassis go back to riding, and worry about fix'n the "correct motor" as time n funds allow.
+1 to what Gary wrote!
Right, needle bearings at the small end were used only in the first run of XS1s. Yamaha went to 22 mm. solid wrist pins before the first year was out. Those were heavy and didn't leave a lot of meat at the small end. The result was that if guys used the hotter 256 cam the way it was designed to be used, the stock rods would stretch, and I'd bet a dollar to a donut that's what you'd find if you compared ID on the vertical axis to ID on the horizontal. Re. the camshaft, you'll know the status for sure if you mike the lobes. Rebuilding the crank would be spendy. If you decide to go that route you might consider Wiseco Hot Rods; lots of bang for the buck.
Right, needle bearings at the small end were used only in the first run of XS1s. Yamaha went to 22 mm. solid wrist pins before the first year was out. Those were heavy and didn't leave a lot of meat at the small end. The result was that if guys used the hotter 256 cam the way it was designed to be used, the stock rods would stretch, and I'd bet a dollar to a donut that's what you'd find if you compared ID on the vertical axis to ID on the horizontal. Re. the camshaft, you'll know the status for sure if you mike the lobes. Rebuilding the crank would be spendy. If you decide to go that route you might consider Wiseco Hot Rods; lots of bang for the buck.
This repair will be a multi-step affair.
1st step get the bike rideable. I've going to put the engine I used in it 2 years ago back in. I only used it 1 summer, 3000 miles on it since I rebuilt it. That's the motor I had in the bike when I rode it to the Iron Horse.
Should be back in and running Friday or Saturday. I do need to replace it's cam chain. I didn't put a new one in when I had it apart. Kind of ironic.
2nd step decide how I want to fix this problem.
Lots of options. Too many to list right now.
That will be for a different thread.
Ain't havin' "spare" motors grand? 
CalsXS2
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Once you start down the path.
Find a good late model motor and transplant the internals if you want to keep it numbers matching.
OR just throw a late model in the chassis go back to riding, and worry about fix'n the "correct motor" as time n funds allow.
Forgive my ignorance. But are you saying you can put a 447 crank in a 256 case? I know you can swap cams but I didn't know you could swap cranks.
This may change everything for me,,,,lol.
You can put a 447 crank in a 256 case, but you will need to also put a 447 cam in to go with it.
Yes, or press a 36 tooth sprocket onto the 256 cam. Early motors (XS1 through TX650) used a 34 tooth crank sprocket under a 17 tooth cam sprocket. In later motors (TX650A to the end) the combination was 18 and 36. What makes life interesting is the cam chain tensioner. Early models used an idler gear in the assembly which is not compatible with the pitch of the cam chain used with the 18/36 combination. The good news: in the XS2, Yamaha changed to cylinder no. 306-11311-01-00, which is the same cylinder that was used in later 447 motors. Late tensioner assemblies will swap right in. IMHO it's a good idea to do that anyway.
