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1963 PV544 rat rod

Very interesting link. On page 37 there are pics of nearly identical damage. But the angle of my flake (opening upward) seems to indicate that I damaged it on installation. Not knocking force from above.
 
Very interesting link. On page 37 there are pics of nearly identical damage. But the angle of my flake (opening upward) seems to indicate that I damaged it on installation. Not knocking force from above.

Compare the top diameter of #3 hole to the others. I wonder if it's a hair smaller/tapered, causing the rings to just barely catch on the deck surface on install.
 
It is indeed suspicious that I would have done the same thing twice on the same cylinder.

I know I'll be SOOOOOPER careful putting the pistons back in this time. I always am, but a 'normal' amount of careful. Just gently tapping them in with the plastic end of my light weight plastic tappy hammer. With a light coat of engine oil on everything.

And double check those ring gaps, although based on bobxyz's link it's probably not butting rings. Just some very slight damage on install, followed by me revving the piss out of it for many thousands of miles. vroom vroom.
 
It is indeed suspicious that I would have done the same thing twice on the same cylinder.

I know I'll be SOOOOOPER careful putting the pistons back in this time. I always am, but a 'normal' amount of careful. Just gently tapping them in with the plastic end of my light weight plastic tappy hammer. With a light coat of engine oil on everything.

And double check those ring gaps, although based on bobxyz's link it's probably not butting rings. Just some very slight damage on install, followed by me revving the piss out of it for many thousands of miles. vroom vroom.

I assume you are checking ring gap by inserting the ring in the bore, square up the ring and then measure the end gap (with all the rings). Do you do this check at multiple elevations in the bore? On an engine which has been in service (and maybe had some 'heavy service') the bore will develop taper with the bottom of the bore being tighter than higher up the bore. If you measure the gap in the mid point of the bore and it is at the lower end of the permissible range you might be losing the gap at the bottom of the bore.

Is it possible that the bore is out of round? Depending on how the ring is oriented relative to the out of round axis of the bore this could mess up your end gap measurement. However, I would expect significantly out of round to manifest itself with other observable issues.

I think you said that these were previously used pistons on which the problem occurred. I am assuming new rings or were they re-used rings? Is it possible that the piston ring lands were worn resulting in excessive vertical clearance between the ring and the piston? If they were new rings were they the correct application for your piston in terms of height of the ring?
 
Frame it and hang it on the garage wall. I do have a little 'drawer of fame' in my tool chest.
- shredded 3rd gear from the M47
- bent/broken rod from my 8V
- broken wristpin from the 16V
- a bent piston from the 16V
 
It wasn't clear from your pictures but what direction/angle are the cracks at ends of the 2 ring lands going on your damaged pistons? Do they go the same direction as the big trapezoidal broken chunk?

I'd think that the machine shop would chamfer / round over the sharp edge after decking the block, both to prevent sharp edges in the combustion chamber and to give a tiny ramp for installing the piston+rings. If it's a sharp edge, I'd be tempted to file it lightly. A few thousandths of chamfer is big compared to the 0.03mm [B21FT] piston to cylinder running clearance.
 
The cracks in the lands themselves are pretty much vertical. I'd have to look at it again. But the flake itself is getting wider going up, which matches the second pic on pg 37. The detonation/hydrolock damaged piston was showing the flake getting wider as it went down. I was just going with the overall 'V' of the flake pointing toward where the problem came from.
 
It does sort of look like the detonation damage on pg 20. Their 'installation error' pics look quite a bit different - far shallower - on the land itself and not extending into the body of the piston, like my flake. And judging by their pics - also direct mechanical failures at the time of installation - the breaks are all clean and fresh. I.e. someone *really* hammered them into a bore, rings poking out and all.

I used a ring compressor, adjusted correctly, and while it's sometimes a minor hassle to make sure it remains flat against the block as the piston slides down in the bore, I'm certainly *not* going to tap a piston in past any resistance - like a ring hitting the block deck.

I'll look things over carefully in that combustion chamber and see if anything looks different. It's very faintly oilier than the others - presumably a bit less oil control happening there because some air went around/behind both compression rings. See if there's anything that looks like it might contribute to pinging vs. the other 3.

I do need to run premium fuel in it, 93 octane pump gas. And I do get an occasional 'sprinkling' of what I feel to be light pinging in certain situations - medium RPMs, light acceleration. It's using a Mallory dual point distributor body with no vacuum advance or retard - just the mechanical advance. And a Crane optical ignition running an MSD 6AL box and Blaster coil.

I've never noticed any real differences in plugs when I've taken them out - but it's got dual DCOE's on it. Which basically means that each cylinder has it's own separate carburettor (the pairs share a float bowl, but have their own throttles and jets). So it could be conceivable that there's something a little 'off' on that one #3 carb that makes it run differently in some situations. They're all 4 certainly jetted and set up identically.
 
FWIW I have a fair amount of experience with factory workers not knowing what they're doing and assembling pistons wrong. Most of the time you're going to get a gouge in the bore as a result, maybe a bent ring. To break a piston, hell to bend a ring even, you've gotta beat on that thing and realize you're probably doing something wrong.
 
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... 93 octane pump gas...They're all 4 certainly jetted and set up identically.

Perhaps on lean side, if timing advance was within ballparks, and if high compression was not the ping issue. Older carburetor based engines, all OEM engines, ran a pinch richer...common when intake manifold could not deliver even flow to all cylinders...so carb was tuned for leanest cylinder(s).

>light pinging in certain situations - medium RPMs, light acceleration..
>Mallory dual point distributor....just the mechanical advance.

Verifying with timing light thru RPM range, and then comparing to a Mech/Vac timing map for that engine might shed some light. Mechanical advance might have been set too aggressive, unless lean fuel and/or compression were the issue(s).
 
It's a pretty high compression ratio. Not entirely intended. I got an R-Sport head on eBay many years ago, used for 'circle track racing' somewhere. It's a great head, flows really well, with the considerable caveat that it was already shaved *WAAAY* down. IIRC it owuld have been something close to 12:1 on a 2.0 bottom end, even higher on my 2.1L. I did some admittedly amateurish work on the chambers - widened them out to match the 92mm bore, smoothed out the sharp edges, trying to get a few more CC's of volume back. And that wasn't enough, so I've been using B21A pistons, which have a small dish (less than B21FT) in them. IIRC the compression ratio - theoretical (not counting the cam) would be about 11.5-ish. Set up with zero height on the pistons and a .036 MLS head gasket.
 
Lol, beware of what you click on, or you'll end up looking at stuff like this: https://www.acm.se/en/product/stroker-kit-volvo-b20-925-mm-2

Which is completely silly.

I'm about 95% decided to just slap one of my leftover pistons in place of the broken one, slap it together, and keep on braaaaaping the Volvo around with wild abandon. And about 5% wondering if I should get a set of forged pistons so this doesn't happen again.

I guess, worst case happens and a piston breaks again, it's not a huge deal, it's not like I depend on the PV for daily driving, or it's a big deal to pull the motor on it.
 
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