Ever seen the like?

[Martin Harris - Moderator]

I took this out of a friend's engine - the cam followers didn't have a mark on them!

I've never seen wear like it. On the exhaust lobe the wear is only on the trailing face of the cam and on the inlet side it's worse on the leading edge but there's a slight indentation on the trailing ramp.

Any ideas other than faulty hardening?

Edited due to the photo being the other way round to the way I thought it was! Inlet cam is on the left...

Edited By Martin Harris on 28/12/2018 16:19:55

[Steve Hargreaves - Moderator]

Oooo..that's..er...that's..er....that's not right that isn't....

[Jon H]

ummmm...yup. am i allowed to guess the brand?

[Don Fry]

Not a clue, never touch the things. The contract goes, you run, I won't interfere with you.

[Bob Cotsford]

too small a base diameter for the amount of lift and badly shaped/sized followers?

[Martin Harris - Moderator]

Posted by Jon - Laser Engines on 28/12/2018 16:27:14:

ummmm...yup. am i allowed to guess the brand?

That's certainly on the way Jon. It's a Laser ASP 120

[Denis Watkins]

Probably, the most expensive part of the operation is the machining

Such a shame to make savings on either the material or the hardening

[Geoff S]

I have seen the like but it was on my 1953 BSA 250cc C11 which seemed to eat camshafts for some reason. Performance would fall off until it wouldn't run. On the last occasion in 1958 he had to drive out with his van to pick me up 40 miles from home. Never with a model engine, though.

Geoff

[Former Member]

[This posting has been removed]

[Jon H]

Posted by Martin Harris on 28/12/2018 16:50:04:

Posted by Jon - Laser Engines on 28/12/2018 16:27:14:

ummmm...yup. am i allowed to guess the brand?

That's certainly on the way Jon. It's a Laser ASP 120

you surprise me. i was going for NGH 30

[Piers Bowlan]

NGH GF38 had a similar problem I think. Could that be caused by the timing being out (bad assembly)?

Edited By Piers Bowlan on 28/12/2018 18:46:50

[Tim A]

Weak valve springs and/or tight tappets operating at high temp and max revs causing valve bounce.

[Martin Harris - Moderator]

Posted by Jason Channing on 28/12/2018 18:21:12:

I recognise that . Its the engine I sold you that was like new, never run, ran perfectly the last time I used it., This was My Auntys pride and joy., No warranty with me mate if your USING CASTOR................ In the case of ASP ,NGH thats how they come as new.........

ASP, SC, Magnum, NGH?

No - this was in a brand new OS70 ! Mind you, Ripmax replaced it without any argument when they acknowledged that Variable Valve Timing shouldn't be a feature!

My own SC120 (touch wood) continues to perform magnificently...

[Former Member]

[This posting has been removed]

[TartanMac]

Dunno if it's clear I had a similar bit of damage to my Saito 60T. Got it second hand it had been run on castor but it was still soft when I stripped it. There was no valve clearance and think the follower gauged the cam lobe pricey for a new cam.

You need to zoom it right up to see it. Not as bad as everybody else's but not sure if the follower will get caught in it.

[Martin Harris - Moderator]

That was usually due to blockage of the oil pipe feeding lubricant to the camshaft. IIRC, a popular modification bodge on some Ford models using this engine was to cut a hole in the bulkhead so that the camshaft could be extracted into the passenger compartment so that the job could be done with the engine in situ!

Fuel used would have been club supplied Southern Modelcraft 10% with 15% ML70/2% castor and I use the same fuel in a wide variety of engines (including my own SC120 FS) without such problems so I don't think this was a lubrication problem.

Valve bounce is an interesting theory but I believe this engine was always used with a relatively large prop in order to pass our club's noise test.

The engine was timed and running correctly but had been unused for a number of years. There was some rusting on the hidden side of the rear bearing but I've seen a lot worse - the ball bearings themselves were not rusted although they may have polished themselves as there was excessive play apparent (the reason for stripping it) after the brief period of running which was not there before, when the engine had felt smooth and free of play.

My gut feeling is that it's been caused by faulty material/hardening - the followers don't show any corresponding wear or damage.

[Chris Walby]

IMHO, Looks like poor cam surface hardning, most likely compounded by marginal lubrication (residue goo and was the cam oiled pre first start after the lay up).

Unlikely to be excessive valve clearance, but if way to tight and the valve springs bind its going bend something or cause the weakest part to fail.

With our race engines I was always told to gently rev (continuously change the revs) and not let them tick over due to the increased risk of cam wear due to low engine speed.

P.S., they look a pretty soft cam profiles, but then it's not a race engine

[cymaz]

Taking of valves, my engineering and flying mate always maintains that valve spring are far too strong.

He says when the matter comes up for discussion “ springs are too strong, inertia is negligible and valve bounce is virtually nonexistent “

Jon, why do manufacturers put ridiculously strong valve springs in? Off the shelf part for every engine?

[Peter Christy]

Had a remarkably similar problem on a brand new Sunbeam Stiletto back around 1968! Whole cylinder head had to be changed under warranty, with less than 1000 miles on the clock! It was still being carefully run in, too!

--

Pete

[Engine Doctor]

Seems very odd that its worn on the side but tops of lobes look reasonable ? I had a camshaft from a very early OS 120 FS that had similar wear but the tops of the lobes and the followers were shot as well. I suppose bits do slip through the QC system . Very Odd . I'm glad it was replaced without fuss .

[Former Member]

[This posting has been removed]

[Martin Harris - Moderator]

Posted by Engine Doctor on 29/12/2018 14:18:40:

Seems very odd that its worn on the side but tops of lobes look reasonable ? I had a camshaft from a very early OS 120 FS that had similar wear but the tops of the lobes and the followers were shot as well. I suppose bits do slip through the QC system . Very Odd . I'm glad it was replaced without fuss .

Maybe a bit of confusion - the second picture I posted was to illustrate that even OS can have quality control problems.

If you look at the geometry carefully, there is a point (corresponding with the damaged areas) where the edge of the follower on its circumference is the only point of contact so the loading must be massive there. The tops of the lobes and followers are virtually unmarked.

On the evidence of the other pictures posted, it seems that the followers could have been designed better when OS came up with their much copied design!

Edited By Martin Harris on 29/12/2018 16:18:37

[Frank Skilbeck]

Posted by cymaz on 29/12/2018 09:46:35:

Taking of valves, my engineering and flying mate always maintains that valve spring are far too strong.

He says when the matter comes up for discussion “ springs are too strong, inertia is negligible and valve bounce is virtually nonexistent “

Jon, why do manufacturers put ridiculously strong valve springs in? Off the shelf part for every engine?

Has your mate calculated the rpm at which valve float starts, it's not really bounce but when the spring can't close the valve fast enough to follow the cam, you'll need the weight of all the components, valve, rocker arm, push rod and cam follower and plot the required closing speed to check it. Did it as part of my mech eng degree some 40 years ago so don't expect me to remember exactly how to do it, but it can be calculated

[Martin Harris - Moderator]

Posted by supertigrefan on 29/12/2018 16:13:01:

Could it be detonation, pre ignition?

I believe those would normally show up as damage to the head and piston. I can't really imagine that any shock load would transfer to the valve gear as the valves would already be closed.

[ken anderson.]

I would say the cause is too much heat and not enough lubrication...….that is if faulty metal isn't the cause...

ken anderson...ne...1..lubrication dept.