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First Top end teardown
- Thread starter macksXS
- Start date
That’s not good.
It could be Mikes. It was in the engine from PO so im not quite sure where it came from. However, there was no "scrapping" issues prior to my disassembly of the top end. So that's why I'm questioning my tightening technique.
On another note, I got 100psi on a cold compression test, so im eager to see where it lies after a few heat cycles. I want to make sure this ATU problem is corrected before I start it back up.
Obviously, the length of the parts (cam, advance rod) hasn't changed. If they fit fine before the only thing that comes to mind is the advance and points housings aren't mounted in tight enough. That could happen if you didn't seat the bearings in all the way on the cam. They must be slid in as far as they'll go. I know it looks kinda wrong because then they hang off the inside of their bore in the case, but that's how they need to be or the points/advance housings won't fit in tight enough .....
The little black bits on the advance side may be from the unit rubbing on the oil seal.
The little black bits on the advance side may be from the unit rubbing on the oil seal.
The ends of the advance rod and the advance unit end of the cam are stepped so the parts will only slide on so far no matter how tight you make their retaining parts (nut or notched ring). So, how much you tightened those items wouldn't be the cause of your rubbing issues.
Obviously, the length of the parts (cam, advance rod) hasn't changed. If they fit fine before the only thing that comes to mind is the advance and points housings aren't mounted in tight enough. That could happen if you didn't seat the bearings in all the way on the cam. They must be slid in as far as they'll go. I know it looks kinda wrong because then they hang off the inside of their bore in the case, but that's how they need to be or the points/advance housings won't fit in tight enough .....
The little black bits on the advance side may be from the unit rubbing on the oil seal.
Thanks 5t, ahh yes, that was going to be my second guess! Intuitively it didn't look right hanging off the end and I neglected to take pictures prior so I went with what "looked right" and made the bearings flush with the inside of the case.
So now, a couple questions...is it possible to move bearings in by loosening/removing the head bolts & lightly tapping both left/right side with a 1" socket? or will i need to pull the engine
? Either way, should the bearings be touching the bearing support lobe?
You should be able to tap them in by just loosening all the fasteners on top of the head. Keep in mind that they both need to be set in the same amount so the cam is centered, so measure and compare the inset side to side .....
I'm not sure what you mean by "bearing support lobe". I'm surprised you didn't have big oil leaks from behind the advance and points housings since they weren't seated in far enough. There's a gasket and o-ring back there but the housing would need to be tight up against the head for them to work and seal properly.
I'm not sure what you mean by "bearing support lobe". I'm surprised you didn't have big oil leaks from behind the advance and points housings since they weren't seated in far enough. There's a gasket and o-ring back there but the housing would need to be tight up against the head for them to work and seal properly.
Was the valve cracked after all??
You should be able to tap them in by just loosening all the fasteners on top of the head. Keep in mind that they both need to be set in the same amount so the cam is centered, so measure and compare the inset side to side .....
I'm not sure what you mean by "bearing support lobe". I'm surprised you didn't have big oil leaks from behind the advance and points housings since they weren't seated in far enough. There's a gasket and o-ring back there but the housing would need to be tight up against the head for them to work and seal properly.
That’s what i was hoping would be possible. I will do just that and measure.
Yeah i didn’t have any leaks coming from there but i did from the engine bolt below the spark plug and from around the bottom of the jug. So i will make sure they all are re-torqued to the most current lb specs. (i was able to find your head bolt torque diagram)
“bearing support lobe” :
The bearing shouldn’t be touching that inside lobe, correct? Do you know what clearance you have right now on your bearings?
Hey Paul, it seemed to be fine after all, but if my acceleration issues persist and the compression test comes out lower than it should. I will be forced to have a look at possible valve leaks.
Hey Guys,
Finally have an update. So i was able to nudge the bearings in a few mm on each side by tapping on them with a 1" socket. They now are even on both sides and the covers fit on like they should. And no more rubbing!
I did a hot & cold compression test:
Cold- 100psi R/L
Hot- 130-135 psi R/L
She starts up fine, idles evenly and sounds great...except, i am still getting resistance upon acceleration past id say 3000-4000rpm it sputters a little & feels like it is "maxed out" doest want to go any faster.
My intuition is telling me it feels like it could be an exhaust or intake leak. Compression seemed ok though. Any more tests i can run to help diagnose? Any threads already talking about this i can read?
My second guess was timing, could it be off?
I'm in denial, i don't want to believe i may have to take the engine apart again
I need some unbiased opinions here
Thanks for all the help!
Finally have an update. So i was able to nudge the bearings in a few mm on each side by tapping on them with a 1" socket. They now are even on both sides and the covers fit on like they should. And no more rubbing!
I did a hot & cold compression test:
Cold- 100psi R/L
Hot- 130-135 psi R/L
She starts up fine, idles evenly and sounds great...except, i am still getting resistance upon acceleration past id say 3000-4000rpm it sputters a little & feels like it is "maxed out" doest want to go any faster.
My intuition is telling me it feels like it could be an exhaust or intake leak. Compression seemed ok though. Any more tests i can run to help diagnose? Any threads already talking about this i can read?
My second guess was timing, could it be off?
I'm in denial, i don't want to believe i may have to take the engine apart again
I need some unbiased opinions hereThanks for all the help!
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You might have a carb problem, as in bad diaphragms. They may have small holes in them so the slides won't lift all the way. The bike will only go so fast and the motor won't rev into the higher RPMs.
If your timing was badly off, it won't start easy like it does. It might be off a few degrees but that shouldn't stop it from revving up into the higher RPMs.
In your rebuild description, you made no mention of what you did to the cylinders and rings, if anything. Did you check for excess wear by measuring piston diameters, bores, and ring end gaps? Did you install new rings and hone the cylinders? Your compression numbers seem a bit low but may come up some after putting a few miles on. But, on the ones I hone and replace rings, the compression is usually better, right around 150, right from the start. That's considered the normal, good value for this motor.
If your timing was badly off, it won't start easy like it does. It might be off a few degrees but that shouldn't stop it from revving up into the higher RPMs.
In your rebuild description, you made no mention of what you did to the cylinders and rings, if anything. Did you check for excess wear by measuring piston diameters, bores, and ring end gaps? Did you install new rings and hone the cylinders? Your compression numbers seem a bit low but may come up some after putting a few miles on. But, on the ones I hone and replace rings, the compression is usually better, right around 150, right from the start. That's considered the normal, good value for this motor.
I replaced the original carbs with the Mikuni VM34 cable driven carbs. Ill have to double check what jets i put in, can't remember off the top of my head. But it still could be a carb issue potentially if my jetting is off.
Thats good to know about the timing. it revs fine when in neutral its only when riding that it feels rough and limited at this higher RPM's.
Regarding pistons. Prior to disassembling the motor was operating fine, however, had some gasket leaks i wanted to address and replace hence the rebuild.
Here is where I excel as an XSnoob in the motorcycle industry. Since it was operating fine prior to my disassembly I neglected to measure the piston diameter, hone cylinders or replace rings. Could this be what's causing the issue?
Thanks again for the guidance @5twins
What ignition? Check that you have proper advance action with a timing light.
I have the PAMCO ignition
Run a battery or you'll cook that Pamco.
Check your advance action with a timing light.
Check your advance action with a timing light.
Ok, good know! So hook up a battery to the ignition to run the test? Do you know of any good threads describing how to do this?
No, I think he meant install a battery on the bike and run it all the time. I guess PMA's are prone to sending out voltage spikes which can kill a Pamco. A battery in the system acts as a "damper" of sorts and absorbs them, thus protecting the Pamco from damage.
Caps are wondrous things but aren't worth a crap to damp out voltage spikes. So many Pamco's have died on PMA cap systems we lost count long ago. Battery based systems and the Pamco's seem to go forever. Resto had one for over 10,000 miles and TWO motors LOL still going strong for it's new owner, Madness has racked up about 8,000 so far on it's Pamco.
And AFAIK yes a timing light prefers a battery to work.
