Scoring on cam lobes and rocker arm freeplay

[Dirt_Boy77]

Hey everyone, I have a 91 XR250R that I rebuilt last year,The topend has about 55 to 60 hours or so on it. The only things I reused when I rebuilt the topend was the main and sub rocker arm shafts,and the sub rocker arms,cam,main rocker arms,cam chain/tensioner were all replaced. Here for the last while I started hearing a rattling over the normal valvetrain(tappet)noise. I got kinda worried so 2 nights ago I pulled the valve cover off. So far I have found the following. Both of the exhaust sub rocker arms have alot of left to right freeplay,the intake sub rocker arms and none of the 4 main rocker arms have any free play from left to right. Could this be causing a rattle with the 2 exhaust sub rocker arms having this left to right freeplay?

I don't hear the rattle until the bike is warmed up and then I can only here it at idle. I also noticed that my new stock cam I put in,the lobes are scored. On one of the lobes the edge of the lobe is chipped off. Not alot but some of it is chipped off,you can only notice it if you are looking close,you just do a quick glance over the cam and you won't see it. And there is some light scoring on the other lobes as well. I put in a brand new oil pump and it is pumping lots of oil to the topend. What should I do about the cam? And could this rattle be coming from the free play in the intake sub rocker arms? Thanks for reading guys.Matt

 

[Dirt_Boy77]

sorry I messed up in my orginal post and it would not let me edit it so I will re type it. I replaced everything when I rebuilt the engine but the 4 sub rocker arms,the sub rocker arm shafts and the main rocker arm shafts. The Cam,cam chain/tensioner were all replaced.

 

[SFO]

What about the wave washers that take up the axial free play?
Were those replaced too?
Did you have axial free play on all the rockers after rebuild?
Stock cam/ w/ stock valve springs is a pretyy mellow set up as far as your cam scoring/chipping goes. How did did you verify proper top end oiling before running after rebuild?
What oil are you running?
If a wave washer broke it could have been injested through the rocker/cam causing the scoring/chipping.

 

[Dirt_Boy77]

SFO after the rebuild to make sure the topend was getting oil I took one of the valve adjustment covers off to make sure oil was spitting out,and indeed alot of oil was spitting out of the hole. I use Bel-Ray EXP Semi-Synthetic oil(10W-40). The wave washers were all good and they were still there on the shaft. Matt

 

[Dirt_Boy77]

I think I may have found the reason for the scoring on my cam lobes. I remember one of last years dirt rider magazines where they did a run down on a bunch of bikes and told you the known problems,what they were good for,etc. In the colum they wrote up on the 86-95 XR250Rs they listed under KNOWN PROBLEMS that if you rode alot of trails like up in the Rocky Mountains it was hard on cams and rocker arms. I would think alot of the rocky mountain trails would be alot of low RPM putting,etc because of the long and steep hills. My singletrack is really tight and I can't ride it to fast because its so tight and I have to be careful that I don't rut it up bad either because my brother,dad ride mountain bikes on it. I have the bike putting at low rpms most of the time on the singletrack trail. What I am thinking is since I am riding at really low rpms alot the oil pump is not pumping near as much oil as it is at say full throttle. Could this be causing the scoring? I took one of the valve adjustment covers off yesterday and started the bike and turned the throttle to where the engine speed was just a little faster than idle,in about 5 seconds or a little more it had the bottom of my gas tank,backside of my front fender,head pipes covered in oil so it is getting enough oil I would think. So the big question is could riding at low RPMS alot like I do be causing the scoring? Thanks guys,Matt

 

[Ol'89r]

Originally posted by Dirt_Boy77
So the big question is could riding at low RPMS alot like I do be causing the scoring? Thanks guys,Matt [/B]

Dirt_Boy.

I don't think that is your problem. Did you recheck your valve adjustment the first couple times you rode the bike after installing the new cam? When you install a new cam and do a top end, everything wears in the first couple times the engine is run and some of the clearance in your adjustment may be taken up. If the engine is allowed to run for even a short period of time with no valve clearance, then you will score your cam. If you have no clearance, it squeezes the oil out from between the cam and the rocker arm and gives you metal to metal contact. This is usually what causes scoring or galling of the camshaft.

Does the cam or rocker arm show any indication of heat. Discoloring or blue color? If so, this may be what happened.

Camshaft break-in is very important also. When installing a new cam you should run the engine on initial start up at a fairly high rpm for about 15 to 20 minutes. Many cam grinders recommend this proceedure. After this is done, you should let the engine cool down and re-check your valve clearance.

Also, those little wave washers on the rocker arms can be replaced with flat washers. Just be sure to leave enough side thrust clearance so that the rocker does not bind in any way.

Just my $ .02 Good luck. :thumb: