Contour Enthusiasts Group Archives Forums General Troubleshooting Compression problem

Guys I need some help.

I have a customer Mark Caslin from Ireland. He has 97 Mondeo 2.5. I sent him new rings and gaskets for the 2.5. He says his compression is now 15:1 instead of 12:1.

I do have to tell you that he got a crank from a Nissan (don't what model) and had it machined.

Do you think the piston rings are the problem or the crank?
Or could it be osmething else?

How did he figure out that the compression ratio is 15:1? A longer piston stroke or having the cylinder heads & block shaved could cause a higher compression ratio.

I donâ??t see how piston rings could cause a higher compression ratio. What does he think caused the higher compression ratio?

I'd bet the crank.

How can he be sure the crank isn't pushing the piston up just that little bit more than a Duratec crank will.

Just how do you put a Nissian crank in a Duratec anyways?

I don't think rings would increase compression past what a new durtec (with correct crank) & rings would already have.

Crank! A bit more stroke it would change the
Compression alot.

head gaskets? that could cause a rise in comp. if they are thinner than the ones on there before but not THAT much. It's probably the Nissan crank. What kind of crazy idea was that?

It has to be the increase stroke of the crank. That, and shaving the head, (a lot), are the only ways to increase the compression ratio that much if the stock pistons are used. I also am not sure why he would choose a Nissan crank over the Ford crank or how it could even fit. For what this guy paid for a custom crank, maybe he could of had a turbo installed to produce more power.What is his goal? Is it possible the guys yanking your leg?

There must be more to this story. What Nissan crank could possibly fit our Duratec? How did it start out at 12:1 anyway?

If the crank could be made to fit and had a longer stroke, he would have needed either shorter rods or special pistons to keep the pistons from rising above the block and jaming into the head.

I doubt that anyone with enough knowledge to know how to make a longer stroke crank work with the proper rod and or piston modificaions would be doumb enough to blame the increased compression on the rings.

My apologies to Shakespear, but something is rotton in Ireland.

Hi, it's my mondeo that is impersonating a diesel.

The crank is original. But Ford did not supply a big enough bearing to fit since the crank needed a lot of grinding.

If turns out that the Nissan Maxima 2.4 uses the same crank and does supply a bigger size bearing, so we used a nissan bearing, ORIGINAL FORD CRANK.

The bore and stroke are standard, block has not been shaved.

The compression pressure is 225 psi. It should be between 130 and 215 psi.

Getting the car back on the road was the intention, not extra power so no crude mods were intended.

If I knew it was the rings I would rip the engine out again (third time), but I would hate to do that and still have the same problem.

Any Ideas,

The only questions I can think to ask:

Did you utilize standard gasket sets only when you re-assembled? Did you use any other gasket/sealant material during re-assembly.

How about any heavy oil, grease, or other lubricant in the cylinders, pistons, bearings, that could have gotten in there?

Some crud could have gotten into the cylinder to produce a temporary elevation of the compression. As soon as the surpurfluous material is burned away, the compression SHOULD go back to normal.