My MK3 does not rev beyond 4500rpm

Carl H said:
I've had several Cams like that, You can hardly tell , speed wise There is more noise and you can see a rocker arm or two doesn't travel as far But I turned decent 1/4 times with one in my MK2A and My MK3 suffered 2 cam failures and It went pretty good. Like I have said my racer friend Gary, Had to wick up his Ex race bike powered by a 750 hopped up motor and he was surprised when he saw the cam. When I sent to Web Cam they said they never saw one as bad. All my bikes can rev over 7 K, some faster than others. Bad cam or not. View attachment 121653
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That's exactly what I have found
I had a combat that was running Castrol r40
One of the lobes was at least halfway gone
The bike ran just the same
 
baz said:
That's exactly what I have found
I had a combat that was running Castrol r40
One of the lobes was at least halfway gone
The bike ran just the same
Click to expand...
That surprises me, but I've not had a cam go south yet. The SS I stuck back in my engine might if I beat on it like I did in my youth. Probably not going to happen though. I put more miles on my bicycles on a roller bike trainer in my garage than my Norton. lol

Grandpaul's worn cam example had a nearly flat intake lobe. My brain says that would be noticeable. Especially if the piston in the cylinder with that intake lobe seized up. Ignore me. I may have a flat lobe in my brain.
 
I had one of those Cheddar Cheese cams. Hiring someone to replace it was not cheap. Interestingly, the bike started and ran fine. The only way you could tell what was wrong was increased valve noise. I kept the old cam: one lobe was worn down to the shaft. I plan to make a lamp out of it.
 
Schwany said:
That surprises me, but I've not had a cam go south yet. The SS I stuck back in my engine might if I beat on it like I did in my youth. Probably not going to happen though. I put more miles on my bicycles on a roller bike trainer in my garage than my Norton. lol

Grandpaul's worn cam example had a nearly flat intake lobe. My brain says that would be noticeable. Especially if the piston in the cylinder with that intake lobe seized up. Ignore me. I may have a flat lobe in my brain.
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The engine was stripped for an unrelated reason which I can't remember right now
The previous owner was running it on R so that veggie oil didn't look after the cam !!and was a pain in the arse because you have to carry on with the R once it's in there unless you completely strip the motor and clean it out
Horrible stuff
 
baz said:
The engine was stripped for an unrelated reason which I can't remember right now
The previous owner was running it on R so that veggie oil didn't look after the cam !!and was a pain in the arse because you have to carry on with the R once it's in there unless you completely strip the motor and clean it out
Horrible stuff
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R is a bad idea on a road bike.

R is great when working within its parameters. But outside of those it’s a bit shit.

Too cold and it’s like treacle. To hot and it’s molecular structure breaks down permanently (and this info is direct from Castrol BTW).

I’d put money on the fact that your cam was killed by cold temp wear.
 
So a cam lobe worn down to the shaft makes no noticeable difference in engine performance?

I'm obviously in the twilight zone. How did I get here?
 
R is really for all roller bearing engines, it stands up to the shear from roller big ends.
A good quality synthetic or mineral oil with a high zinc content to protect the cams and followers
 
On the first post Javifoto said that he recently installed new pistons and rings in the bike. He would have to remove the barrel to do that, so he would be looking right at the cam. I think we can assume that a badly worn cam would have been noticed and replaced. Perhaps he will comment.
 

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This might be a good time/place to remind some folks that it is common courtesy to respond to people who are trying to help if you post a query…
Just my inner Mr. Etiquette coming out.
 
worntorn said:
On the first post Javifoto said that he recently installed new pistons and rings in the bike. He would have to remove the barrel to do that, so he would be looking right at the cam. I think we can assume that a badly worn cam would have been noticed and replaced. Perhaps he will comment.
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It’s a looong thread, so easy to miss snippets, but waaay back in post #57 the OP said he suspected cam lobe wear.

Although, early on, he said the only things he’d not done was split the case, in post #100 he added that “The cylinders and head are the only two parts of the engine I did not do myself because the previous owner told me it was done”…
 
The posibility of crankcase overpressure limiting the revs has been mentioned and I noticed that a pcv breather is fitted. Could this valve have been installed the wrong way round? I have no experience with Reed valve breathers so don't know if the engine would even run for long like that.
That still wouldn't account for the black oil or stiff pedal so I still recommend a complete strip down - NOW!!
 
Fast Eddie said:
R is a bad idea on a road bike.

R is great when working within its parameters. But outside of those it’s a bit shit.

Too cold and it’s like treacle. To hot and it’s molecular structure breaks down permanently (and this info is direct from Castrol BTW).

I’d put money on the fact that your cam was killed by cold temp wear.
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You could be right
I really don't like the stuff
I love the smell but that's all
 
Schwany said:
So a cam lobe worn down to the shaft makes no noticeable difference in engine performance?

I'm obviously in the twilight zone. How did I get here?
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My cam from memory was half worn definitely not worn to the shaft
I can only say that I couldn't notice a difference in performance it certainly outperformed my mk2a that I also owned at that time
 
Fast Eddie said:
It’s a looong thread, so easy to miss snippets, but waaay back in post #57 the OP said he suspected cam lobe wear.

Although, early on, he said the only things he’d not done was split the case, in post #100 he added that “The cylinders and head are the only two parts of the engine I did not do myself because the previous owner told me it was done”…
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Sorry, I missed that one. Still, I think it's highly unlikely that the previous owner would have gone to the trouble of installing new pistons while leaving a scrubbed out cam in place. My guess is that this is not the problem.

Glen
 
Hybrid racer mentioned a pvc valve possibly installed wrong way round. I would remove it to see if it made any difference. Cheap and easy.
 
worntorn said:
Sorry, I missed that one. Still, I think it's highly unlikely that the previous owner would have gone to the trouble of installing new pistons while leaving a scrubbed out cam in place. My guess is that this is not the problem.

Glen
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I agree. Cam timing is far more likely. To me, it sounds a lot like badly retarded ign, but the OP has checked and triple checked this. It’s becoming quite the mystery for the poor fella !
 

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