Finally found the problem

[funkytrunk92]

Well, as some of you may know, I purchased a cobra a few weeks ago and have been having various problems. After a compression test showing very little compression in cylinders 7 and 8, we decided to go ahead and tear the motor down. Well, I made it to the head gaskets, and they looked ok. Then I got to the pistons. Sure enough 7 and 8 were broken between the rings.

I am actually pretty happy to have actually found a problem. I would have hated to have done all that and then try to guess what the problem may be.

So looks like I'll be buying new pistons, bearings, etc.

I was hoping some of you could point me in the right direction, brands of pistons and things like that as this is my first official motor build........or is it rebuild? Anyway, any help I can get will be greatly appreciated. Thankfully the piston walls look pretty good. As soon as I get the funds together, I will be getting to a machine shop to have the block, heads, etc checked and also trying to order some pistons. I know the pistons will set me back, but I don't want to cheap out and be pulling the motor again anytime soon.

Look forward to hearing from you guys. I 'll be researchin parts prices
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[Marlboro_Man]

SRP + Probe are some names i've heard good stuff about, but i have no personal experience with them.

If your replacing them , might as well get some that will bump your compression and have some good valve reliefs in them if you ever plan on putting a set of good heads on it.

Talk to rick91gt on here, he would probably be willing to help you find what you need as well as plan a build up for the future. www.RNHperformance.net

 

[smittyb]

How many miles are on it? Are you planning on having it bored over? Any head work?

 

[88Stang331]

I'd suggest going to a 306 so you can clean the block up, and then a nice set of internals...SRP or Probe come to mind.

 

[funkytrunk92]

Actually, the previous owner states that it is a 306. I am going to have the machine shop check all of that to make sure. I the car has 160,000 miles, but even if it has been bored before, it looks likes the bearings and all are stock. Maybe not, but they are pretty worn none the less. If it is a 306, I am crossing my fingers that I won't have to get a new block, but I guess I'll do whatever it takes to get it back on the road, right.

I think the heads recently had a valve job, but again I am going to have the machine shop give everything the onceover. Would it be worth it to have the intake and heads ported or cleaned up or whatever while I have it off. It just the stock cobra stuff, gt40 heads etc.

 

[eagleautosports]

Post edited:

I'm trying to sell a 306 rotating assembly from DSS. It's completely balanced and ready for assembly with DSS Pro Series pistons, rings, bearings, even a high volume oil pump. PM me if you're interested in talking further.


--Daggar--

Friendly reminder: We do not conduct sales within the forums.
Thanks,
Daggs

 

[smittyb]

Sounds like you already know what to do. Intially you stated the bores looked good, so if it already has GOOD aftermarket pistons, why pay for a new set? You could just replace the broken two, have the block honedand the crank ground, and put new bearings and rings in.

 

[funkytrunk92]

Sounds like you already know what to do. Intially you stated the bores looked good, so if it already has GOOD aftermarket pistons, why pay for a new set? You could just replace the broken two, have the block honedand the crank ground, and put new bearings and rings in.

Well I'm not sure how good the other pistons are, I am going to have the machine shop check them over for me. I question them if 2 cracked like that. If they are good, you really think that just replacing 2 is ok? I'm all about spending less money, but I also want to do it right the first time.

Also do you think that a machine shop could tell if they are forged or hyper pistons.(I'm not even going to try and spell hyperwhatever !)

 

[smittyb]

A good machine shop should be able to, I have had some unbelievably stupid run ins with a few though. There is nothing wrong with reusing the pistons if they are in good shape. Just make sure you get the block honed and a new set of rings.

 

[funkytrunk92]

update
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Well, my wife took the block,crank etc to the machine shop. She just called me and informed me that the shop measured the block and guess what...........it's not a 306? The hits just keep on coming. Thats actually good in though because there is piston wall damage and it will need to be bored. So now I can be sure it is a 306!
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I'll keep you guys posted.

 

[BlownFiveLiter]

If it's been taken out .030, there's probably still room to bring the bore out to .040 over as long as the cylinder walls aren't scored from the pistons being broken. Then you'll just have a 308 instead of a 306. Measure the cylinder bore in several locations both across and down to make sure you're within spec to allow the overbore. If you're in good shape to go larger, I'd say go ahead and do it, pick up some new parts, and have fun with your freshly rebuilt engine