some pistons can sit like that ,,, depends on specView attachment 405273
Is it just the camera angle, but the piston looks slightly proud on the l/hand side?![]()
its level, its does look higher though in the pic. had a straight edge and vernier all over it.View attachment 405273
Is it just the camera angle, but the piston looks slightly proud on the l/hand side?![]()
its really only the water jacket ports that look iffy ,,, whats the head like though .ok i have this JB weld and its what its for. The low areas are a few though so ill fill them with this.
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head is great, off a rebuilt block. i jsut want to be sure, just cleaned the worst back and little but enough to concern me to fill them.its really only the water jacket ports that look iffy ,,, whats the head like though .
i do not know the cam spec but all engines i have came out of boats. all same spec from measurements i have taken. Barley anything has been taken off the head so i reckon it will be ok as is.B20 you can probably go to 0.1mm proud. I assume the cam is quite mild? Do you know the specs? What you need to be careful of is the dynamic compression ratio if running a mild cam, you'll get knock. If it's a hotter cam in the Pentas then it should be fine.
No it's not simple, as your rig shows - I'm not sure if you have a gudgeon pin in there but you should, unless the measurement between the pin hole to base measures out exactly square and the same on each one.Those piston crowns do look high. The block looks to me like it's been pushed across one of those horizontal surface grinders that reconditioning shops used to use a lot. Simple job to machine piston crowns down though.
View attachment 405272
Don't go there - most con rods of that era can show a slight out of true - resulting in the piston not perfectly square. You are not building a race engine, leave well alone. And where does 4 thou proud come from? 15 more likely fine, if you need it. And this is from race engine experience, not heresay. Aand, an engine running at 4000 rpm is not a highly stressed unit, ok i's not a put put, but even a road car sees higher rpm than that.its level, its does look higher though in the pic. had a straight edge and vernier all over it.
I always secure the pistons using a bar through the gudgeon pin hole, it's easier to see in this image of a Small Block Ford piston.No it's not simple, as your rig shows - I'm not sure if you have a gudgeon pin in there but you should, unless the measurement between the pin hole to base measures out exactly square and the same on each one.
Once jigged up it's easy, but you wouldn't expect joe blogs to have the kit to do it properly.
Nice jig, good to see it done correctly. But, I guarantee you that j.bloggs would not have that jig, or even consider the need for it. Maybe a decent engine reconditioned would.I always secure the pistons using a bar through the gudgeon pin hole, it's easier to see in this image of a Small Block Ford piston.
View attachment 405300
According to the engine builder, these were at or less than 0.010" proud of the block at TDC. but when the engine was revved, there was a 'knocking noise' I machined the crowns down, but one of the pistons had a crack in the top ring land, so the builder got a replacement and I machined that too.
And when I said it was (and is) a simple job, it is. Reboring is a simple job, Joe Blogs probably doesn't have a boring bar in his garage either. But if I was that Joe Blogs, I wouldn't expect someone who does machining work to fall off their chair if I came in with a set of pistons and instructions as to what I wanted taken off each one or all.
All the pistons had witness marks, the one with the cracked top ring land had a more pronounced mark, but didn't look gruesome. Of course, the unknown (to me) was the thickness of the head gasket that the builder had used. Even with stout rods, there is still crank whip. Personally, I would never have piston crowns above the deck in a finished motor unless there were recesses in the head, as on this Ford Model 'A' head destined for a Pendine runner.When you machined the crowns or rather inspected them, had they been touching the head at less than 10” proud? I would suspect not, unless the damaged one was? A v8 crank has loads of main bearing support, can’t see the rods growing more than a couple of thou at rpms...
Have you tried to measure the low (corroded uncleaned) areas with dial gauge? I've seen worse and still seal with a composite gasket.
Classic fly-cut blocks and heads can have quite pronounced cutter marks with no detriment to sealing.