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Update,
I measured the ring end gaps and rod clearances on number 1 they are just right.
It seems as though one of the rods is bent maybe, no matter which bore I put it in on rod in particular seizes when torqued up.
I have another set of rods and pistons from the little mules old engine, I have asked the guy with the flypress to swap my new piston from the bent rod to a rod from that set.
I was thinking about why this might have happened, would a discrepancy in the cylinder head combustion chambers do this (compression ratio)? there is a visible difference in the depth of one of the chambers on this head I have got.....
pic in a sec
I have taken it to the man with the flypress
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Last Edit: Jun 5, 2010 12:14:14 GMT by suterman
1985 Bedford CF2 camper 1991 Volvo 240 Turbo |
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left to right 4321, you can see on number 2 the chamber is less recessed than the other 3. look at the top left of number 2, there is no step down into the cc from the face like on the others. Colour adjusted to make it stand out a bit better.  |
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Last Edit: Jun 5, 2010 12:26:21 GMT by suterman
1985 Bedford CF2 camper 1991 Volvo 240 Turbo |
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kee
Posted a lot
Posts: 4,988
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thats a bit dodgy, looks like its been ported and polished but not finished
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I did some cleaning up of the casting marks in the runners and some minor tidying of the bowls.
To top it all I notice the piston CROWN to gudgeon pin varies greatly from piston to piston over the old ones (sticking up by as much as 1.2mm above block deck whereas the stock ones are flush)
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1985 Bedford CF2 camper 1991 Volvo 240 Turbo |
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One guess would be it has suffered HG failure in the past, possibly had a hydraulic lock on that pot and bent the rod when it was turned over.
Looks as though it has had the head skimmed, showing up a casting imperfection. I say that because the machined parts (valve seats) are all at the same distance from the deck, which is the datum for the machine that cuts them.
As the bowl is a cast and not machined surface I'd expect to see a little bit of variance in that shape (admittedly not that much but it's possible). That'll cause a minor rise in compression but you shouldn't notice it tbh
See what it does with the replacement rod on that piston. If it rotates freely and nothing makes contact when the head's torqued down (engineer's blue!) then you should be okay.
--Phil
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10mpg
Club Retro Rides Member
Posts: 4,253
Club RR Member Number: 204
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^^^^That sound about right to me, and damn good advice to!
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The Internet, like all tools, if used improperly, can make a complete bo**cks of even the simplest jobs...
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Jun 10, 2010 19:01:25 GMT
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New rod is in, now it all turns smoothly but you can see my next problem  |
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1985 Bedford CF2 camper 1991 Volvo 240 Turbo |
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Jun 10, 2010 20:18:19 GMT
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The caps do need to be on their original rods. They are machined as an assembly so the tiny variances between each rod assembly will be enough to cause the problem you describe. sorry but I have to disagree with that statement... having worked rebuilding engines it was of paramount importance to keep caps and rods together as when the holes were bored in the end of the rods for the bearings they were done as a pair, as you say though the differences would be minimal.. but it WOULD be a difference |
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What's the height of the pistons over the deck at TDC versus the thickness of the headgasket?
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PhoenixCapri
West Midlands
Posts: 2,683
Club RR Member Number: 91
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The pistons are standing pretty proud, but I have seen this on a crossflow I built and because the the head gasket depth it was fine.
Has the block been skimmed?
Measure how much they're up by, then measure the old head gasket if you have it. If not as a very (very) rough guide measure the new one and divide by 2. if the pistons stand no more than 50-60% proud than this thickness then you might be ok.
But really its going to be a case of built it up with the head and see if it turns over. Possible waste of a gasket, but at least you'll know.
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The headgasket thickness is 1.2mm compressed (at the fire rings) The head has been skimmed for freshness. There were some areas of corrosion that I cleaned up and filled with JB weld, it needed skimming after that. The block has not been skimmed. The old pistons were flush with the head, I have a feeling these new pistons are not brilliant quality.  Last night I took 4 copper washers measuring 1.15mm thick and used them to space the head off the block and popped some headbolts through. A couple of the pistons touched the head. The head I used was stripped so I need to measure again tonight to take valve travel into account. |
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Last Edit: Jun 11, 2010 6:49:53 GMT by suterman
1985 Bedford CF2 camper 1991 Volvo 240 Turbo |
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The caps do need to be on their original rods. They are machined as an assembly so the tiny variances between each rod assembly will be enough to cause the problem you describe. sorry but I have to disagree with that statement... having worked rebuilding engines it was of paramount importance to keep caps and rods together as when the holes were bored in the end of the rods for the bearings they were done as a pair, as you say though the differences would be minimal.. but it WOULD be a difference Er, you might was the re-read what you've quoted there ;D Suterman, that head kind of looks like it mught have warped and been skimmed flat in the past. I've not seen a head with a difference as great as that in CC before. Not sure I'd want to use that myself. |
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1962 Datsun Bluebird Estate - 1971 Datsun 510 SSS - 1976 Datsun 710 SSS - 1981 Dodge van - 1985 Nissan Cherry Europe GTi - 1988 Nissan Prairie - 1990 Hyundai Pony Pickup - 1992 Mazda MX5
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