camshaft clearance

[scrambler]

Dear All,

Just assembling the head and bumped into a new issue. I didn`t notice this earlier when I dismantled the engine, but now it seems my camshaft has some freeplay if I move it up and down. I have 3 sets of camshaft and brackets, there is a radial freeplay with all. The clearance between the bearing and the shaft is not mentioned in the manual. Anyone else experienced this? I can`t measure it exactly as I don`t have a micrometer but I t`m afraid this much clearance is not ok and the camshaft will be knocking. The smallest freeplay by feel belongs to the camsaft pictured below, but I think someone else before me tried to fix this by hammering the ends of the shaft to get a better fit... What do you guys think?

[yamman]

If the play is present when the unit is bolted to the head then you have an issue, sometimes play can be felt when in a sectional state but not when bolted to the head, hope this helps.

[scrambler]

Yeah, I fingertightened the bolts and there`s a clear freeplay for each set of brackets I have. What a poor design to support a camshaft only by two bearings in a 750cc engine. I`m trying now to fit needle roller bearings there.

[Rasputin]

Ideally, there would only be running clearance in the cam mountings, taken up by oil. In an engine with some miles on it, the clearance will get bigger. As all the forces acting on the bearings are in a downward direction, the cam followers and chain tension will wear the hole only on the head side. If lubrication is positive feed and oil has been changed regularly, minimum wear will be present. As yours seem to be rather more than that, then you have a choice, new bearing housings, or as you suggest needle roller conversion, this would be better and quite easy to do if the cam journals are OK.
Pictures of the cam journals and completed needle roller fitment would be nice, if you complete the job.
My engine although has only 12,000 MLS on it has a distinct top end rattle on one side, I am thinking this could be the cause. Wouldn't it be nice to lift the rocker cover off to have a look, with the engine in the frame.

[scrambler]

I bought the needle bearings as they were cheap and took the whole stuff to a machinist. He advised me not to go with the bearings as the cam journals are not designed for this, they are not made of hardened steel, they are designed to be running in a bearing case where they are supported evenly on the surface, not only by the tiny surface of the needle rollers, so the journal will wear out quite soon. He also thinks that such a high clearance might be normal, as the followers and the chain press the cam downwards, so it shouldn`t cause too much rattling noise unless it is worn out excessively. It all makes sense to me and sounds reasonable, as all the three camshaft-bracket sets have similar clearances. Still, it would be nice to know what the clearance looks like in a new bracket-cam pair, but I didn`t find anything about it. Btw, axial freeplay and the top metal chain guard may also cause rattling sound, the former could be solved by shimming, the latter by cutting off a piece of the guard (oil distributor???), there`s a bulletin for each of these issues.


Cheers,


Greg 

[Rasputin]

Hi Greg. The reference you provided made me look at the bulletin regarding the cam chain shroud. I can imagine that this is the cause of the noise on my engine, it only makes the noise at around 2500 to 3000 rpm. I have tried altering the tensioner push rod and inserting a rubber spacer in between the rod abutment and the large threaded adjuster. Makes no difference, so I am not going to do anything about it, do some more miles see if it gets any worse.
As for your problem, it should be possible to put a hard sleeve on the cam journal and run needle rollers on it. Why oh why didn’t they use ball bearings as on the XS650 engine? Really simple and robust.

[scrambler]

Hi Rasputin,



Finally I decided not to do anything to the cam, as the clearance is so minimal that the free play is only noticable when it`s bone dry. When I lubricate te bearing it does not move at all, it seems totally fine, the lack of oil was quite misleading. As the rockers are forcing the cam downward I think there has to be a huge wear in the brackets or on the journals to produce a noticable noise, so I don`t think this is the issue in your engine. Both in my engines the chain guard was badly scratched, so in addition to what the service bulletine suggests I cut off about 10 mm from both sides of it. Perhaps in your case this may be an issue, if you remove the valve cover caps can you look into it?



Also, in my engines, the valve stems were in really bad condition so I had to replace all the valves. I don`t know what sort of noise they would make but might be related to what you have. Let me know when you find out.



Another thing: in the bike I`m rebuilding, I`m planning to drill the head oil supply orifice from 1.5 to 1.7mm, as far as I know the newer engines used this mod to increase oil supply in the head. Also, I had machined a little pocket in the cam brackets where the oil can sit in and lubricate the cam bearings right after start.

[Rasputin]

Hi All. At the moment I am loathed to remove the engine just so a I can look and see if there are any witness marks on the chain guide. I intend to leave well alone until something more sinister shows up. I can nearly be sure that this is what is making the noise. Although the bike is showing only 13,000 mls, it has at some time had the head off judging by the orange silicone around the head gasket area. Reading through the tech bulletins, they make mention the use of RTV silicone sealant to cure leaks on the top end.
At this time would they have carried out the mod to the cam chain guard?
At some time in the future I may strip the bike totally to re-finish the frame etc, it is original but really shabby. There again you can only have an original bike if nothing is done. I’m torn. Anyhow I am really pleased with the way it runs, I like riding it too much to have it in bits. More later.

[scrambler]

Hey Rasp,

I have a replacement engine with no number stamped on it with the factory upgrades that DOES have the same guard. My `73 stock engine that has been rebuilt with a new camshaft in warranty has the same guard. So it`s very likely that yours has that as well. Did you try to take a peek via the valve caps?

[sammiuk]

Hi i just wondered if you removed the studs that hold the camshaft boxes that you could fit the cam chain without hearing or revetting it , the boxes do need sealing to the head it's just a thought has anyone tried this