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Author: Subject: Overheated Zetec = compression loss
ChrisL

posted on 5/1/20 at 06:18 PM Reply With Quote
Overheated Zetec = compression loss

Whilst get the SC conversion done I've managed to overheat the engine, massively as I didn't notice a huge split in a hose and when checking the header when cold there was still some water in it, at the bottom of the tank. Was too busy trying to tune and drive to look at the temp gauge, so here we are but at least it explains the oil vapour coming out of the breather!!

I've done a cold compression test and the results don't look good:

This is in PSI, I checked twice!

Cyl Dry Wet
1 25 45
2 10 50
3 25 50
4 60 135

So now what to do? Is it worth getting the engine up to temp and re-run the tests? is it worth attempting to salvage if so is it just new rings? What would cause issues on the head?

I've bought an endoscope to see if I can find any bore damage, before taking the head off.

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cliftyhanger

posted on 5/1/20 at 06:38 PM Reply With Quote
Those figures are a disaster.
Th head needs to be off, checked that isn't bent like a banana or worse, pistons out to check the rings....
You may be lucky and "just" need a hone/rings and head skim. But if you stumble across a good engine I would be buying it.

The figures imply the pistons are not holed, or a wet test would have made no difference.

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steve m

posted on 5/1/20 at 06:39 PM Reply With Quote
From experience with a 1700 crossflow, that I seriously overheated it until it seized, on the way back from an Skcc run

The block and head were used again, but the crank, rods, pistons, piston rings and valves were all binned

If your lucky, and it didn't seize, then I would rebuild it, with new rings and bearings, assuming everything else comes with in tolerances

steve





Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at




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steve m

posted on 5/1/20 at 06:41 PM Reply With Quote
The compression figures were done with "wide open throttle" ???

as if not the figures are usless

steve





Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at




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britishtrident

posted on 5/1/20 at 08:41 PM Reply With Quote
As above use wide open throttle and all spark plugs removed. Soak some Redex down the bores for a few days before the next test.

Severe overheat damage to piston rings rarely shows up immediately usuall months latterbut most times there is no issue.





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ChrisL

posted on 6/1/20 at 10:51 AM Reply With Quote
Thanks for the replies, so the orifginal figure were not WOT so I've done them again, I'd consider the first set as wet as I could still see the oil down the bores. I started the engine and let it idle for a about 5 mins so the water temp was just starting to rise. Not fully up to temp but I've got fussy neighbours!

Cyl Wet Warm
1 40 25
2 20 15
3 65 40
4 135 80

Quite surprised that the pressure held went down when the engine was warm!

Will have look with an endoscope when it arrives and take the head off at the weekend

Cheers
Chris

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MikeRJ

posted on 6/1/20 at 12:41 PM Reply With Quote
Serious overheating will soften the crown and the lands of the pistons, which can then smear and trap the rings, even if a full seizure didn't occur. The rings themselves can also lose their temper which prevents them sealing well. Pistons exposed to such high temperatures should no be re-used.
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big_wasa

posted on 6/1/20 at 01:35 PM Reply With Quote
My old man cooked a zetec until the valve seats dropped.

Zetec's are getting harder to get but I would still get another.

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steve m

posted on 6/1/20 at 02:18 PM Reply With Quote
The fourth cylinder was doing all the work, to keep the other three spinning according to
your compression readings!

Also, as Mike said, my piston ring gap on the pistons, had broken up, so the rings had no were to sit, so all four were scrapped

I did use the engine again, but it was a FULL rebuild with known parts

steve





Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at




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snapper

posted on 6/1/20 at 03:10 PM Reply With Quote
I recon its a warped head.
You can skim a warped head but its not the ideal way to go as you will increase compression in the chambers in an uneven fashion, it will still run ok but in warping a head is a skilled (and expensive) job.
Best to pull the head off and check head and block for warping.





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ChrisL

posted on 7/1/20 at 06:12 AM Reply With Quote
Cheers chaps,

Just bought a new engine with a reported 80K on it. When I get time I'll take the old one apart to see what caused the issue. Just wondering if it's worth doing anything to the new one before I fit it? I'm planning on putting in ARP corned bolts atm.

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steve m

posted on 7/1/20 at 06:58 AM Reply With Quote
Put brand new hoses on ?

steve





Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at




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ChrisL

posted on 7/1/20 at 08:58 AM Reply With Quote
haha, yes probably a good idea!
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procomp

posted on 8/1/20 at 03:59 PM Reply With Quote
Anything over 107deg warps the head.
we just had a head skimmed by 4tho to correct a warped head after a 110deg moment when auxiliary belt came off at Oulton with 2 laps to go.
we also had new rings fitted i should mention also.

Cheers Matt

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ChrisL

posted on 8/1/20 at 05:00 PM Reply With Quote
Ahh that would fit with it reaching 114 degrees!
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cliftyhanger

posted on 8/1/20 at 05:45 PM Reply With Quote
A new timing belt would be wise...
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ChrisL

posted on 8/1/20 at 08:08 PM Reply With Quote
On the list so far:

Timing belt
Water pump
Spigot bearing
Plugs
Oil and water flushes

Cheers
Chris

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