Topic: 500-4 race cam problem

[mark7even]

Hi Guys,

I'm running a 500-4 race bike. We've just fitted a rebuilt engine which after 30 mins running on break in developed a top end rattle. Removing the rocker cover revealed one of the in lobes on the cam and the follower very heavily worn and blued. There's loads of oil at the top end and all the other cam lobes and followers seem to be ok. It's a new camshaft  and followers. Am I looking at a breakdown on the hardening of the follower or cam? I've pressed down on the valve and it appears to be moving freely. Any thoughts on causation?

Cheers, Mark

[turboguzzi]

if it's a race cam, there's precious little clearance UNDER the rocker arm when the lboe passes under it, i luckily discovered that when turning the engine by hand and feeling a strange resistance after the build.
I managed to grind a few tenths off the rocker bottom arc and surely saved what could be total failure. shame that megacycle doesnt tell you to do this check in their leaflet.

have a look at the bottom side of the rocker, between the slide pad and the rocker shaft boss to see if it touched there.

bad timing but could be nice to see some pics of the bike and mess.... we can always learn.

[calj737]

To TG's point, below is a MegaCycle 126-20 cam for my 500 where these 2 points interfere. I don't know if thats your issue, but thought a picture might help.

[turboguzzi]

exactly, the dark spot over that rib. if you have a similar spot on the rocker, then that could have been the cause

[mark7even]

Thanks for your response. I've checked the underside of the follower and no sign of any contact, likewise on the valve cap. I've attached some photo's of the wear. I've had this problem to a lesser degree over a season with the inlet followers showing slight wear, but nothing like this, after break-in. I've one meeting to run this season, so trying to work out the best option. I've a spare engine, so tempted to put another cam and follower in the head. Cheers

[turboguzzi]

ouch

happened to me ages ago in a street cb500/4 due to a clogged oil supply. but even with a new cam and rocker i would be wary of running the bottom end with all that swarf in it....
where do you race?

[bwaller]

Definitely an oil supply issue. You never mentioned what cam?

[mark7even]

I'm racing CRMC in the UK, GP 500 class . The problem occurred at Rijecka, great fast track, issue occurred after 16 laps gentle warm up. Strangely there is no swarf at all anywhere evident, oil beneath the lobe was clean. The exhaust lobe and follower on the same cylinder is fine, no blue on either the lobe or the follower. As it's sharing the same oil bath I'm assuming that it's not a lube issue. Just turning the engine over by hand I'm getting a good supply of oil to the head. I'm going to check this shortly as I've just removed the cam. I'm running fully synthetic oil, same as on my other engine which is built to the same spec.

[turboguzzi]

but still i'd drop the sump and check the oil pump strainer. with that type of wear it would be more like steel powder rather than visible swarf...

then oil might get to head but maybe gallery in head is clogged towards the center?

maybe just bad luck with heat treatment of either specific lobe or follower, whats the cam indeed?

been once to rijeka but never raced there, did look a bit scary in terms of run off, etc.  long way around for you, were you doing the german "Grab the flag" thing?

[mark7even]

H Turbo, thanks for your response, I'll pull the sump and check the strainer. I've just taken the cam out and turned the engine by hand, there's good oil supply to the four cam journals.
The engine and cam are from John Davis, I've seen previous posts on the forum from Honda Freak about the engines and bike. I was running this engine because it's fitted with a dry clutch and I wanted to keep the temp down. The running temps in 30 deg ambient was lower than my wet clutch engine.

The run to Rijecka was do a Euro FIM 500 race, my previous meeting was at the Classic Festival at Donnington. The Croatian trip was a complete nightmare, we were busted for illegal camping with the motorhome, the blow-up was the icing on the cake! The circuit is a stunner, bit tired but great to ride. I was pretty gutted because I think I would have run well.
Cheers

[bwaller]

It's a crying shame. With the cam removed is the "oil track" on the cam bearing surface clean? You certainly have oil in the head, and the damage is limited to one lobe, but there is some scuffing on the cam where it rides in the head there.

I have seen hard weld cam lobes worn badly in a hurry mated with OEM used rockers. In this case the rockers are NOS?

[classic bike tuner]

scheck for wear/clearance  of the rocker schafts  if its a cover with half rods  you migt have a problem

[Big Jay]

Springs ay coil bind?

[scottly]

Definitely an oil supply issue.

1+ It takes heat to discolor steel like that, and the only possible source of heat is friction.

[mark7even]

Hi Guys,

Sorry for the delay in responding, I work at sea and I'm just back on dry land once more. Thanks for all your inputs, the cam and followers are on their way back to the supplier. I'll update you on their verdict, however they seem to be leaning toward a failure in the hardening.

Cheers, Mark

[turboguzzi]

makes sense... an oil supply issue would have more than one lobe suffering.