1980 Yamaha SR250 Worn Camshaft & Rockers

[Motomike93]

Hello Do The Ton members,

My name is Michael and I am new to the forum however I have a project bike that I feel Do The Ton members have experience with.

I have two 1980 Yamaha SR250 engines one with 20,000 miles and the other with 4970 miles.

I have never used either for riding and acquired them as is with existing wear. I have had both running though.

The engine with 4979 miles has a wicked knock in the head which I found to be worn a worn out camshaft and rocker pads. The engine with 20,000 miles is smooth as silk with good rocker pads and camshaft . Attached are photos of each engines rockers, one with significant wear and one in good condition.

My problem is, I want to carry my project forward with the lower mile engine and just replace the cam and rockers but have concerns about the rest of the engine due to a clear lack of lubrication in the top end. Now there was a TSB for these engines for lack of lubrication in the top end which neither of these engines received but I feel 5000 miles to wear out components that bad is crazy.

Let me know your thoughts on carrying forward with the 5000 mi engine and some potential things I should look at.

Thank you!

 

[teazer]

Hi MotoMike and welcome.

That rocker is well worn to be sure and that means the cam and rockers have to be replaced at least. And possibly the head if the cam has picked up on the bearing surfaces.

There are two ways you could go. One is to try to work out what went wrong on the low mile motor and then fix it. It might just need a new head, cam rockers etc but it's also possible that the crank has damage depending on the mode of failure.

Or you can just use the slightly higher mile motor which seems to be perfect. 20,000 miles is not an issue on a modern bike motor and as you have already discovered, low miles are no guarantee of a good motor.

I would use the low mile motor and strip the other in your spare time over winter.

 

[irk miller]

5k is absolutely crazy to have that much wear, unless someone rode with the theory that the tighter the better on rocker timing. I would run the 20k engine while it's good and dig deeper on the 5k. TBH, I don't believe the 5k motor is actually 5k miles.

 

[Motomike93]

Hi MotoMike and welcome.

That rocker is well worn to be sure and that means the cam and rockers have to be replaced at least. And possibly the head if the cam has picked up on the bearing surfaces.

There are two ways you could go. One is to try to work out what went wrong on the low mile motor and then fix it. It might just need a new head, cam rockers etc but it's also possible that the crank has damage depending on the mode of failure.

Or you can just use the slightly higher mile motor which seems to be perfect. 20,000 miles is not an issue on a modern bike motor and as you have already discovered, low miles are no guarantee of a good motor.

I would use the low mile motor and strip the other in your spare time over winter.

5k is absolutely crazy to have that much wear, unless someone rode with the theory that the tighter the better on rocker timing. I would run the 20k engine while it's good and dig deeper on the 5k. TBH, I don't believe the 5k motor is actually 5k miles.

Thanks for the input teazer and irk miller. Yea it is very difficult to believe even with the cylinder head lubrication issue that there would be that much cam wear.

At any rate, I have decided to go forward with the "lower" mile engine and do a top end on it since the exterior of the engine is in much better condition. The cylinder wall still has some good cross hatching on it. I am going to measure the cylinder walls, piston skirt and if I am within tolerance toss some new rings and reuse the piston with a light hone on the cylinder.

For some due diligence, I am going to inspect the oil pump and measure it for tolerances against what I have in my SR250 service manual making sure it is not out of spec and the cause for excessive camshaft and rocker pad wear.

 

[teazer]

Looks like the fix was to restrict oil to the crank in order to allow more oil to flow to the top end. on the wrecked motor, what do the cam bearings and the surfaces in the head look like? Honda used to have a similar problem with some of their singles and many early 4 cylinder bikes and typically the cam bearings in the head were damaged and had to be machined out and bushed if the damage wasn't too bad.

I would recommend that you check those surfaces and also make sure there is no restriction in the head and fit a restrictor in the crank and flush the oil out and you might be OK.

Or take the top end off the higher mile motor and clean it up and fit it if it's OK.

 

[Motomike93]

The first three photos are the camshaft of the motor with worn out rockers and camshaft. The last two are the cams of the smooth running engine.

Everything else on the “low” mileage motor looks good in terms of wear except the rockers/cam which were shot. Attached is a photo of the cylinder which still shows cross hatching. I have telescoping gauges and micrometers that I used measure the bore and piston and there is virtually no measureable wear. I’m going to give it a light hone and toss in new rings with the original piston.

 

[Motomike93]

Going through all the oil galleries to make sure everything is clear. While going through the head I noticed the only feed hole to the head is rather small. Has anyone ever increased the size of it for more oil flow? Or just stick with the roll pin in the crank TSB?

 

[teazer]

Is that needle roller bearing as bad as it looks? Should be replaced.

 

[Motomike93]

Is that needle roller bearing as bad as it looks? Should be replaced.

It doesn’t look that bad but I’m going replace that roller bearing plus the ball bearing on the chain end. With the lack of upper lubrication it can’t hurt having new bearings up top.

 

[arjanhoekstra]

I would strongly suggest you take the whole engine apart and completely rebuild it. All the crap from the worn rockers and cam would have circulated the engine and collected in the bodem of the crankcase probably not visible to the eye. Tear down the bottom end, inspect everything and replace all bearings. If you just fit new rockers and camshaft they will most likely suffer the same fate after just 500-1000km. A waste of time and money.

 

[Motomike93]

I would strongly suggest you take the whole engine apart and completely rebuild it. All the crap from the worn rockers and cam would have circulated the engine and collected in the bodem of the crankcase probably not visible to the eye. Tear down the bottom end, inspect everything and replace all bearings. If you just fit new rockers and camshaft they will most likely suffer the same fate after just 500-1000km. A waste of time and money.

I am going to continue with doing just the top end with new cam bearings as everything else I have measured has been well within service limits. Minimal time to do the work and the cost is a head gasket, cam bearings and ring set.

Worst case it doesn’t last I have another engine that didn’t have cam wear I can toss in and rebuild the engine if it fails over the winter.