Engine wear in a Mk2 Square 4

[Paul_Linden]

Been meaning to post these pics for a while now. The first is the camshaft that came out of my Mk2 square 4 during the rebuild last year next to the replacement (thank you to club spares). The second picture is one of the cam followers, again old on the right new on the left. The amount of wear is horrendous. So not really a bad thing that happened to my Ariel, just an unpleasant thing.

camshaft

followers

As the rest of the engine didn't show similar symptoms of drastic wear I was curious as to why this might be. I think I found the answer when I checked the valve springs. In the photo below the middle pair of springs are what came out of the bike - these are much longer than specified. A set of new springs of the correct length are the two outside springs. Is it plausible that valve springs that are too long and too strong could cause the rapid wear seen above?

springs

[marcus whatling]

That's worn out the extra force due to stronger springs won,t help .Could be down to lack of oil or running with dirty old oil .
Would have made an interesting valve timing graph . I have checked timing using a graph with valve lift over degrees which should show worn lobs . Have you seen the big end shells are they badly scored .
Marcus .

[Paul_Linden]

The big end journals were all right, only some light marks that polished out. New std shells went in at rebuild time.
The metal from the cams and followers must have been cleaned out before i got the bike as it wasnt in the sludge that i cleaned out from the engine, the oil tank and oil pipes.
Apart from the main bushes, cams and followers the motor was in very good condition, std pistons and barrels with little wear, primary gears showing little wear. 10k miles on the clock, which is plausible knowing the bike's history.
Now fitted with morgo pump an inline oil filter.

[nevhunter]

Cams and followers are the most critically loaded part of many bikes. You need the antifriction additive types of oil or they will scuff the surfaces as yours have. Having strong(er) springs will make it more likely. It's not "normal" wear. It's a breakdown of the oil film. Local heating and tearing of the surfaces which are made of very hard steel . Nev

[david.anderson]

The standard valve springs for the square 4 are not very strong. There are two different sets of springs that were used. VS455 is used for the early mk2, while VS518 is used for the later mk2 which also uses the steel umbrella shroud in the centre of the springs. Both sets of springs use a different top collar. The correct length should be 1.625” for the outer spring of both sets of springs.
A spring that is a bit longer or stronger would not cause the problem that you have encountered unless the spring was becoming valve bound at full lift in which case rapid wear would be expected. Excess cam bush wear would also be possible due to cam flex. It would be worth checking the fitted valve spring length and the length at valve bound to see if that was the problem, although from the number of coils it does not look that way. At full lift a valve spring should be at least .060” from valve bound.
But the most likely cause of the wear is as Nev stated,the use of the wrong oil. That is the kind of wear normally seen in “flat tappet” engines (for want of a better term) where a normal motor oil is used. I have seen that kind of wear on numerous occasions on various vehicles and as recently as last week on an MG. Make sure that you use a high zinc (ZDDP) oil that is meant for vintage air cooled engines and ensure that you smear the cam and lifters with a cam breakin lube on reassembly.
David

[Paul_Linden]

I'm using Penrite Classic HPR40 25w/70 oil in the square 4, which I believe has the anti-scuffing zinc additives.

[nevhunter]

IF it wore when the oil was used it didn't do the job then. Perhaps it was a pre existing condition? This sort of wear is fairly common in vertical twins Early Truimphs, BSA's and Rudges Ariel RH, and some earlier OHC cars without roller cam followers. Unless the cam is running in a trough to hold oil it starts dry often so a good reason to not rev it straight away. Nev

[Paul_Linden]

Indeed, this cam wear happened to the bike before i got it. I was given to understand that the bike was laid up for a few decades, so this could have happened as long ago as the 1970s. When i got the bike i rebuilt the engine, and since then have been running on Penrite. The engine is oiltight - yes, really - but i cant say the same of the clutch or the gearbox!