19 replies to this topic

[fenghuang]

Under normal conditions (ie not race conditions and assuming nothing else fails) is it possible for a camshaft to get excessively worn, and if so what would be the symptoms?

[Carlos W]

Yup.

As the lobe wears you won't get as much lift, which will reduce performance

[fenghuang]

Presumably the effect of worn exhaust lobes would be different from worn inlet lobes?

[Spider]

IMO, you're more likely to wear a cam from around town driving than on the race track. Lubrication of the Cam Lobes is ONLY from what's thrown off the Big End Bearings. At low RPMs, there's low Oil Flow and the centrifugal force from the big ends is low, so little Oil is getting splashed about. This is why we run new Cams at minimum 2000 RPM for 20 minutes.

 

Rather than guess if it's worn, and in line with what Carlos has said, measure the lift at the Valve. If you can set the tappets, you can do this simple check, though you'll need a Dial Gauge. Check all valves.

 

Generally speaking, worn Inlets can increase the low RPM torque particularly with stock grinds, however, to off set that, a worn timing chain increases the high RPM Power.

 

Worn Exhausts usually cost high RPM power.

[Northernpower]

If you haven't set the tappets you should check the clearances. If you come across an excessively large clearance and the locking nut is still tight its a strong possibility the lobe has worn

[fenghuang]

The clearances were set. :-(

I'll have to look up how to measure the lift. (And invest in a dial guage.)

The timing chain has been replaced.

Edited by fenghuang, 22 July 2016 - 09:29 AM.

[ACDodd]

High ratio rockers and high poundage valve springs also reduce road mileage expectations.

Ac

[fenghuang]

All standard on mine.

[Allrounder]

I'd also check that the push rods rotate when your turning the engine over.

[fenghuang]

I'd also check that the push rods rotate when your turning the engine over.

Im not sure I follow. Rotate?
All the push rods were removed recently when I had the head rwfurb'd.

[nicklouse]

 

I'd also check that the push rods rotate when your turning the engine over.

Im not sure I follow. Rotate?
All the push rods were removed recently when I had the head rwfurb'd.

 

ok two things here.

 

you did put the push rods back into the same cam follower didn't you?

 

when the engine is running with the rocker cover off the push rods and the valve springs/caps/valves do also rotate about their axis.

[fenghuang]

Yea, the pushrods went back in the right order.
And thanks for the clarification.

Edited by fenghuang, 22 July 2016 - 01:01 PM.

[Allrounder]

Where the cam followers run on the cam aren't flat! So as the engine turns over and the cam lifts the follower it should also rotate it in its guild to prevent wear to followers face and can lobe, which you should see by looking at the top of the push rods. Dot a bit of paint on the top/edge of the push rod and turn the engine over to check.

[Spider]

If you haven't set the tappets you should check the clearances. If you come across an excessively large clearance and the locking nut is still tight its a strong possibility the lobe has worn

 

Likewise, if the tappet clearances are closing up, then it's likely valve recession in to the valve seats is going on. Usually happens more so with Exhaust Valves on Leaded Heads with Unleaded Fuels, but not exclusively.

[Carlos W]

If you haven't set the tappets you should check the clearances. If you come across an excessively large clearance and the locking nut is still tight its a strong possibility the lobe has worn

The tappets should be set when the cam follower is on the heel of the lobe, not the nose.