Professional Engine Builders Needed

[fastfive_ogt]

Ok here's the question. My brother just build an engine for his chrysler conquest. Its a mitsu 2.6l engine. Wiesco pistons, shot peen rods, stock polished crank, and all arp fasteners w/ clevite bearings. He has an sds stand alone and 255lph fuel pump w/ 750cc injectors and a garrett 60-1 turbo(huge turbo). The problem is we just took the short block back to the machine shop because the sides which the wrist pins reside look all melted and scored up the cylinder walls on those sides. Even some alluminum is at the top of the bore on those sides. The 2 middle cylinders are the worst and the 2 outers are not as bad. He tuned his car and the afr's on boost where 11.6 across the boards. Also the egt backs the 11.6 afr up by coinsiding. Anyway we tried to argue that the piston cylinder wall clearance was too tight. Of course trying to recoupe himself and his work the machine shop owner said it was detination and tunig problem. He measure the clearance and it was .004 which falls indefinitely in spec. How could the engine be lean if the afr's are 11.6? That is impossable isn't it. I thought maybe he had the block in the press not straight and when boring oblonged the cylinder walls possably. Unfortunitly we can't measure the scored side for failure to get an accurate reading due to wall scoring. He had heard of wiesco pistons having this problem due to improper piston fitment. Is that possable? On both sides or the pistons the rings are like melted into the lans. Seems like detonation but doesn't really look like it. Not to mention how is det. possable w/ 11.6 afr's. Plugs where cold enough and timing definitly retarded enough. This just boggles my mind so any info or opinions on this subject would be much appreciated. Thanks again in advance.
Mike

 

[fastfive_ogt]

What no body wants to get into this one? Where going to clean the cylinder walls and measure across there to be sure the bore was bad......

 

[twicks69]

You can have 11.6:1 AFR's and still have detonation. Your timing was likely too advanced for the gas being used.

If it was machine shop - related, it could be an issue of that you (or whoever installed the pistons) didn't use the right amount of gap in the top and 2nd ring. (in my case, I am running an .018" top ring gap and a .020" 2nd ring gap based on the boost levels I am using, and the rpms that I go to).

It could be that the bore job was done improperly, or that they didn't use a torque plate to do the align hone.

It certainly sounds like the rings were gapped too tight, leaving not enough room for expansion, along with detonation occuring.

 

[wt71gas]

Was the engine block machined with a torque plate? I assume it was not and if that is the case it could be possible that if the machining was within specs but on the tight side then maybe with the head bolted on it tweaked it enough to make it just that much too tight. Obviously tuning somehow could be an issue but that is an idea too.

 

[tkelly27]

Did the shop know that they were forged pistons? Forged units can have more thermal expansion, and generally need a different bore size.

Head torque could have done it.

Do you have a log of the run where things went kaput? Doesn't take a whole lot at high boost to nuke an engine.

11.6 is enough to give you detonation on a high comp, high boost engine.

 

[GVR4592]

I'm more interested in the method they used to attach a pressed pin rod to a floating pin piston. I've seen some interesting methods and some of them didn't work so well. Can you post some pics of the damage?

 

[gsxtacy]

Agreed.^

I cannot assess much just by Text. Post up some pictures of all the damaged components.

I have seen many failures....and root cause of failures is usually a very wide scope of errors in assembly.

Scuffing of cylinder walls can also happen if the piston/wall clearance is too excessive in the bore...

 

[Maglin]

Well melted ring lands and rings are not signs of bad tuning. Most often caused by no oil or as posted above tight rings. Usually tight rings will break the ring lands on the pistons. My very first though was someone didn't put the c-clip in all th way for the wrist pin but they are on stock rods. I would personally put a 4G63/64 in it personally. Those 2.6's are not all that strong and the 2v heads really are out dated.

Torque plate or no .004" is more than enough for Wiesco's. I believe mine said .0025 minimum piston to cylinder wall clearance. Most machine shops mess up on the piston measurement as you don't measure them where every other manufacture measures them. I don't remember where off the top of my head but you should have kept your stuff and it was in the documentation that came with the pistons.