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Posted: Mon May 27, 2013 6:22 pm
by mgbv8
DaviesDJ wrote:Ok guys, now winging its way to me are a set of NASCAR Carrillo used 6 inch rods for my new build!
going to grind my 4.6 crank down and offset to 89mm at the 1.85 inch diameter as required! Have been discussing options with mike(kiwicar) who has been great with advice. BUT was wandering what piston options to go for??? Wrist pin is 0.86, and I can have a comp height of much above 1.2-1.22 inch. Think the ford modular 3.7 inch big bore flat top/shallow dish is my best bet but was wondering if anything else is about??? Perhaps a bit bigger then 94mm??? Cos use a Chevy but don't like be idea of drilling out the small end/ wrist pin hole to .927 or whatever - seems a big jump taking away a lot of metal. Any thoughts??? Ohhh by the way, rods and bearings 144 dollars.
I got my engine shop to fit bronze bushes into my chevy rods to take the Rover wrist pins. they drilled an oil hole in the top of the rod and through the bushes as well.
This way if I decide to change for a chevy piston I just have to get the bushes popped out
I'm sure my comp height on the Omega's is small like the 1.22" you mentioned.
Posted: Mon May 27, 2013 8:58 pm
by DaviesDJ
Yes, that's a versatile way of doing it. I think I will fit / have fitted bushes into the pistons, has anybody done that I wonder?
Posted: Tue May 28, 2013 4:46 pm
by bigaldart
Temperature gradients in the pistons are too great, I would certainly not go that way, bush the little end of the rod, we even made our own offset bushes to get zero deck when we ran Volvo pistons, no issues whatsoever. Just can't see anyway a bush in a piston will work.
Alan
Posted: Wed May 29, 2013 7:37 pm
by mgbv8
Bushing the pistons doesnt seem a good way ??
As Alan says, I think the variance of expansion rates between the ally piston and a bronze bush could lead to other problems.
I thought the idea was to meet the larger size of the chevy wrist pin holes on the rods? To bush the pistons to match would mean taking ally out, so why fit bushes into the pistons to achieve this?
I had my rod bushes made fully floating and the Omega's have circlips so I can take the pistons off myself.
Best thing is to decide on what pistons you will end up using, then tweak the rods to suit. The beauty of bushing the rods to suit off the shelf pistons with smaller wrist pins is that its all reversible
Posted: Sun Jun 02, 2013 4:14 pm
by DaviesDJ
The rods i have purchased are now fixed and they have a very small small end at 0.833 inches, so the nearest piston i can realistically get is a o.866 inch ford modular whic will mean openning out the small end about 1mm. I have chatted to a few people and this seems dooable
But in an ideal world would like pistons to fit:-)
Posted: Mon Jun 03, 2013 5:45 pm
by bigaldart
If the rods are bushed, which is likely they will be at least 60 thou wall thickness, boring out by 1mm which is 40 thou or thereabouts shouldn't be a problem, only takes away bushing material and can't therefore weaken the rod.
Alan