Engine rebuild spec info request
Thread Starter
Tech Contributor
Joined: Aug 1999
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From: Connecticut, USA
Engine rebuild spec info request
I've been on this forum for years but never been here before. Since I'm now cleaning up my 72 350 engine I what to know what the engine guys think
.
This engine has 55k miles on it and ran good when I started a body on resto several years ago. The engine is just about the last thing I need to go through.
The cylinders are between .002-.0025" oversize which is what the ridge is. The pistons are the stock 8.5 cast ones with .001-.002 wear on the skirts. So my piston to bore clearence is between .002-.0045" among the cylinders.
Several guys told me to just flex hone it and rering it. Will this be enough to get a good seal? What is the point where a rebore and hone is needed? I was thinking of new flat top Hyper pistons to bump up CR a little bit,but I have new WP S/R Torquers with 67cc chambers so this may bump up the CR to 9:1 I don't want to go over 9.5:1
The cam is a 260H,performer intake, headers, stock ignition. This is not a drag car by any means just a driver. It is a modified TH400 and 308 setup.
So what would you do~ hone and re-ring, new pistons, or bore and hone .030" ?
Thanks for the help.
Gary
.
This engine has 55k miles on it and ran good when I started a body on resto several years ago. The engine is just about the last thing I need to go through.
The cylinders are between .002-.0025" oversize which is what the ridge is. The pistons are the stock 8.5 cast ones with .001-.002 wear on the skirts. So my piston to bore clearence is between .002-.0045" among the cylinders.
Several guys told me to just flex hone it and rering it. Will this be enough to get a good seal? What is the point where a rebore and hone is needed? I was thinking of new flat top Hyper pistons to bump up CR a little bit,but I have new WP S/R Torquers with 67cc chambers so this may bump up the CR to 9:1 I don't want to go over 9.5:1
The cam is a 260H,performer intake, headers, stock ignition. This is not a drag car by any means just a driver. It is a modified TH400 and 308 setup.
So what would you do~ hone and re-ring, new pistons, or bore and hone .030" ?
Thanks for the help.
Gary
Last edited by gtr1999; Jan 18, 2005 at 05:33 PM.
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,135
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From: Connecticut, USA
Originally Posted by comp
is money tight ?? is so do the cheapie job.. if not do it right
Gary
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Joined: Sep 2000
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From: The Top of Utah
Originally Posted by gtr1999
Not so much a money issue, I just have been to several shops and they all had different answers. I didn't expect this to be a big deal, but they couldn't tell me at which point I could use either the old pistons or new std ones before having to rebore. I would rather not cut the block if I don't have to since it's a numbers block.
Gary
Gary
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Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,135
Likes: 3,938
From: Connecticut, USA
Originally Posted by CFI-EFI
Why do anything to it all? Was it smoking? Did it fail a compression test? It doesn't sound like you're concerned about building big horsepower. If you DO want better performance, wrap this numbers matching engine in a plastic bag and buy a core to build.
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Gary
Race Director
Joined: Sep 2000
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From: The Top of Utah
In that case, I think your last stated intentions are the way to go. You might take the pistons and the block to a machine shop for a hands on opinion. Possibly knurling the pistons is in order. If that isn't successful, the dreaded cutting is inevitable. Also, these days, there is a different perspective on honing. Depending on your ring choice, it may be best to leave the bores alone. For your purposes, I think you're on the right track.
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Safety Car
Joined: May 1999
Posts: 3,651
Likes: 5
From: Atlantis
Cruise-In I Veteran
Everyone's got one and this one is mine.
JMHO..... but that thing is loose enough to really run GOOD.
You can run the guts out of them with .005 clearance and not scuff the pistons.
That's the clearance I used to run on all my circle track engines.
Of course cast and hyper. pistons usually run with a little less clearance than that.
If you want to tighten it up just a little and if you want it to run a good bit better;
Replace the stock pistons with a set of flat top pistons.
That will take away a little of your .005 clearance.
Should bump the compression up a little to around 9.5:1.
Do a light smooth hone on it using a lot of oil on the hone and then use a set of moly rings. They will seat and seal and it will run fine.
The only extra cost in doing this will be around $125~$150 for a new set of pistons.
While you have the heads off do a cleanup valve job and have the shop do the 30* backcut on the valves.
Sounds like you have all the 'fixins' to have a real nice running engine there.
As I said, this is JMHO.
JMHO..... but that thing is loose enough to really run GOOD.
You can run the guts out of them with .005 clearance and not scuff the pistons.
That's the clearance I used to run on all my circle track engines.
Of course cast and hyper. pistons usually run with a little less clearance than that.
If you want to tighten it up just a little and if you want it to run a good bit better;
Replace the stock pistons with a set of flat top pistons.
That will take away a little of your .005 clearance.
Should bump the compression up a little to around 9.5:1.
Do a light smooth hone on it using a lot of oil on the hone and then use a set of moly rings. They will seat and seal and it will run fine.
The only extra cost in doing this will be around $125~$150 for a new set of pistons.
While you have the heads off do a cleanup valve job and have the shop do the 30* backcut on the valves.
Sounds like you have all the 'fixins' to have a real nice running engine there.
As I said, this is JMHO.
