Compression problem - CEG Archives

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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 don�??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.

Originally posted by Bill @ SigLM:
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?

If by chance you mean that he ran a compression test and it came out that low, it almost has to be out of time. Can't trust the marks on a non OEM crank.

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.

The only other possibility I can think of is that there may be some oil on the cylinder walls from doing the rework. The extra sealing that it would cause may bump the psi up a little (or Kg/CM

).

Have you tried running the engine yet? If it is oil (I mean a thin coating, not liquid) it will go away after running the motor.

I\As I think here, are the ring gaps O.K.?

But thats about it.

Funny, most people have trouble with low compression.

Originally posted by windrain:
Hi, it's my mondeo that is impersonating a diesel.
.....
The compression pressure is 225 psi. It should be between 130 and 215 psi. ...

Welcome onboard.

Not sure where you got those specs, or how you translated them to compression ratios quoted in Bill's post above, however 225 doesn't seem far off, only +5%.

Can't find compression ratio or pressure spec in my service manual. All it says is lowest cylinder compression should be at least 75% of highest. Manual then gives a table to do the math for you by listing highest pressure from 134psi to 222psi and giving the corresponding 75% lowest pressure figure.

So, unless you exceed the variation spec, you are probably OK.

Car is very hard to start if that is relevant.

Standard gasket sets were used, they were very thin in any case. Nothing non-standard done with sealant either.

I don't think there is any heavy oil or grease in the cyclinders as there is no smoke or smell and engine has been driving for 200 miles.

Ring gaps is a possibility.

Does anybody know if Ford tried out new pistons and rings from the 2000 contour in Europe first, in which case I would have needed the newer rings?
The problem in Ireland is that Ford only do two engine parts, bottom end and top end and seem to know or care nothing about parts.!

Thanks, guys.

When the compression is found to be too high in one or more cylinders, this would be an indication of excessive carbon build up in the engine. This can only be corrected by performing a chemical de-carbonizing process on the engine (specialized service), or by removing the cylinder head(s) and physically removing the carbon that is attached to the cylinder portion of the head(s) and the tops of the pistons.

With your engine work did you remove the cylinder heads? Were they cleaned and/or the pistons cleaned als? Was there any carbon build up?

Obvious question, did you use new plugs.....

Rings do nothing for compression ratio.

A compression test is affected by many factors including elevation and barometric pressure.

Even if you ran NO head gasket (ZERO compressed height) verses the stock 1mm compressed height it would only raise the compression ratio by 1 point.

Like I told you on the NECO site Bill. Something is fishy and it's definitely not either of those two parts!

A chemical de-carbonising process was performed prior to the crank going. Compression was normal then. Heads were removed on rebuild and as much as possible cleaned up.

Engine has now done some 300 miles and no change so I don't think it is oil or grease in the cyclinders.

Electrics and fueling have been tested with no faults found.
Emissions ok also.
I've run out of ideas!

its your flux capicator my does it all the time

but really no the only thing that can effect this would be what is listed about, it probably the ring gap and or placement of the gaps, in my honda they had to be a special way, dont know if this is true for duratec's

Never thought of the flux capicitor.

I must check that last year when I get a chance.

Does anyone know of any special fitting instructions for the rings?

I've changed the oil from 5/50 to 15/50 and the car is much better, but not perfect.
Does anyone have views on oil thickness.

This is an old discussion.

I say the crank. Even a few mm of error will give huge differences in compression.

Originally posted by Nate'sTour:
This is an old discussion.

I say the crank. Even a few mm of error will give huge differences in compression.

He has the same crank, just new bearings. Stroke is same. It is an interesting problem though.

Originally posted by windrain:
I've changed the oil from 5/50 to 15/50 and the car is much better, but not perfect.
Does anyone have views on oil thickness.

That seems a little thick... The Contour/Mystique Duratecs take 5/30 and some of the newer ones (2000) say 5/20. Just a thought.

How does the car run??

You said it starts hard, which would say that either the battery needs charged or the compression is high. High compression puts a greater load on the starter.

Go read what Ford and other carmakers recommend in the rest of the world.

Check out bobistheoilguy.com

The have forums for "oil nuts" and are just as passionate about motor oil as folks here are passionate about Contours and Mystiques.

Seems North America goes for these thinner oils like a 5W20 and 5W30 while Europe and Asia and Austraila call for a wider range of oils.

So it wouldn't surprise me to read that Ford recommends 20W50 for the Zetec in Europe, say during the summer.

On an interesting, and somewhat related note, it seems running oil longer intervals between changes DOES NOT result in more engine wear. In fact, there have been a few studies that say as the oil gets older, the wear decreases as indicated by performing oil analysis.

I'll post another topic for discussion, if I can find the article, or the link over at the BITOG site.

It was interesting.

For a very long time, I've been doing Mobil 1 for 6 months or 8-10K miles, whichever comes first.

You can see my oil analysis here:

And all of them are here: http://tlcc2000.dyndns.org/Oil_Analysis

The 2000 MPV is a 2.5L Duratec run almost exactly 6 months and just about exactly 5000 miles.

Ok, I'll stop the hijack and let you go back to the original discussion.

TB

Tick over needs to be high (like 1200) to keep the car from rattling, even then the steering wheel shakes.

On driving the car is very very fussy below 2500 rpm, like it needs to be clutched to do anything.

Above 3000 rpm car revs very smoothly.