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Help with compression results #1621287
03/06/2018 09:13
03/06/2018 09:13
Joined: Mar 2006
Posts: 85
Northumberland
shawtek Offline OP
Club Member 1721
shawtek  Offline OP
Club Member 1721
Reaping the fruits

Joined: Mar 2006
Posts: 85
Northumberland
Hey all,

So my coupe has been off the road for a long time.. finally got her back home and ready to fix her up. She has had the usual tuning work done to engine (ported, 3 angled, forged etc.) by Barbz many moons ago and was running OK one day and then rough as hell the next.

Still idles but very lumpy... seems to sort herself out under load but doesn't sound perfect... and then you remove the oil filler can to see a lovely puffing of exhaust frown

Did compression test yesterday -> 50 > 50 > 150 > 150 > 150

Not what I expected... what's the chances of this being the head gasket blown between the first 2 cylinders? I know it is quite uncommon on these engines but maybe more common after rebuilds?

If it is the gasket... what else would i need to do the job apart from the gasket set? (new head bolts too etc.?)

p.s... car has always had low oil pressure at idle too... but again i hear that is quite common on tuned engines and to take the guage readings with a pinch of salt too?

Heres hoping you all come back saying its the gasket!

Thanks in advance!

Re: Help with compression results [Re: shawtek] #1621295
03/06/2018 10:37
03/06/2018 10:37
Joined: Apr 2010
Posts: 979
norwich, norfolk
adam16vt Offline
Enjoying the ride
adam16vt  Offline
Enjoying the ride

Joined: Apr 2010
Posts: 979
norwich, norfolk
I could well be wrong but I thought smoke from the oil filler cap meant a cracked piston, I believe it’s called ‘chuffing’ or something like that

My old smoked from there and had low compression, I never investigated it and just dismantled it

Re: Help with compression results [Re: shawtek] #1621302
03/06/2018 16:42
03/06/2018 16:42
Joined: Jul 2008
Posts: 357
The Shire
skeandubh Online tongue
Club member 1598
skeandubh  Online Tongue
Club member 1598
Making a profit

Joined: Jul 2008
Posts: 357
The Shire
Did you do the compression test on a hot or cold engine?

What you could do is check the compression on the 2 dodgy cylinders at the same time. If the gauge needles move up together, when cranking the engine, then it could be head gasket failure between the cylinders. Obviously you need two gauges. However, it seems to me whatever the problem is, it’s likely you’re going to have to remove the head to investigate fully, even if the fault is common to both cylinders.

Why would a tuned engine have lower oil pressure at idle than a standard engine of the same type? How much lower is lower? Fiat spec at idle is >1bar @100degC.


Re: Help with compression results [Re: shawtek] #1621303
03/06/2018 16:55
03/06/2018 16:55
Joined: Mar 2006
Posts: 85
Northumberland
shawtek Offline OP
Club Member 1721
shawtek  Offline OP
Club Member 1721
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Joined: Mar 2006
Posts: 85
Northumberland
Great idea.. I will borrow an extra gauge and try testing both at same time, thanks.

I tested with cold engine.

I just read something on here saying that engines that have had work done to them can run lower pressure.

Re: Help with compression results [Re: shawtek] #1621307
03/06/2018 17:07
03/06/2018 17:07
Joined: Apr 2014
Posts: 209
norwich
sharman Offline
Making a profit
sharman  Offline
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Posts: 209
norwich
Put a single squirt of oil (2ml or so)in the cylinder and do the comp test again. If it jumps back to where it should be then the oil has sealed the gap between the piston and the bore. Means you've got ring or bore damage. If it doesn't change then your problem is above the piston.

Re: Help with compression results [Re: shawtek] #1621313
03/06/2018 19:16
03/06/2018 19:16
Joined: Jul 2008
Posts: 357
The Shire
skeandubh Online tongue
Club member 1598
skeandubh  Online Tongue
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Making a profit

Joined: Jul 2008
Posts: 357
The Shire
Just another thought.

Did you check the compression with all spark plugs removed? If there was a head gasket issue between 2 cylinders then some pressure would be lost through this failure and out of the other cylinder to atmosphere.

Regarding bore damage, can I suggest putting a boroscope down into the cylinder, via the spark plug hole, and checking the cylinder walls. I used a cheap boroscope, less than £100, and it was good enough to show me the honing (Honing photo) on the cylinder walls. I’d imagine if you had bore damage serious enough to lose compression then it would be more evident to see.

Last edited by skeandubh; 03/06/2018 19:17.

Re: Help with compression results [Re: shawtek] #1621328
04/06/2018 07:24
04/06/2018 07:24
Joined: Sep 2006
Posts: 14,703
FCSS 01684 593187
Countrycruising Offline
Club Rep Europe, member 914
Countrycruising  Offline
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I AM a Coop

Joined: Sep 2006
Posts: 14,703
FCSS 01684 593187
Low compression and chuffing from the oil filler sounds like cracked pistons to me, next I'd suggest a leak down test.

Re: Help with compression results [Re: shawtek] #1621339
04/06/2018 12:37
04/06/2018 12:37
Joined: Mar 2006
Posts: 85
Northumberland
shawtek Offline OP
Club Member 1721
shawtek  Offline OP
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Reaping the fruits

Joined: Mar 2006
Posts: 85
Northumberland
Just tried another test with plugs removed on both cylinders... same result and no loss of pressure... so doesn't look like head gasket frown

So cracked pistons or rings if luck then?!

Am I right in thinking that I wouldn't be able to buy just 2 Wossner forged pistons, but instead have to buy a full set?

My alternative option here is to put a spare standard engine in and put her back to standard and sell the forged engine on for somebody as a project. I would rather not do this though, as its still going to be a mission to put her back to standard anyway.

Re: Help with compression results [Re: shawtek] #1621346
04/06/2018 15:37
04/06/2018 15:37
Joined: Sep 2006
Posts: 14,703
FCSS 01684 593187
Countrycruising Offline
Club Rep Europe, member 914
Countrycruising  Offline
Club Rep Europe, member 914
I AM a Coop

Joined: Sep 2006
Posts: 14,703
FCSS 01684 593187
My money would be on cracked ring valleys over rings being the issue, PEC can supply single pistons if you know the size, was it rebored when rebuilt?

Re: Help with compression results [Re: shawtek] #1621350
04/06/2018 16:56
04/06/2018 16:56
Joined: Mar 2006
Posts: 85
Northumberland
shawtek Offline OP
Club Member 1721
shawtek  Offline OP
Club Member 1721
Reaping the fruits

Joined: Mar 2006
Posts: 85
Northumberland
Oh cool, thanks for that.

Pretty sure it was rebored but will check the paperwork.

All the work had been done well before I bought the car and the paperwork shows the car having all the work done by Barbz.. and then another full invoice a few months later for exactly the same with zero charge. (maybe because it it failed first time round?)

Car has done over 30k miles since (73k total) but starting to regret not reading all the papers before buying. I can't get rid though, still in lovely condition apart from the engine smile

Re: Help with compression results [Re: shawtek] #1621356
04/06/2018 19:16
04/06/2018 19:16
Joined: Dec 2005
Posts: 7,124
Lightwater, Surrey, UK
DaveG Offline
Club Member 311
DaveG  Offline
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Joined: Dec 2005
Posts: 7,124
Lightwater, Surrey, UK
I've never heard of forged pistons "cracking" like this, but that's not to say it doesn't happen...I wonder why it would be? The normal reason is a fuelling problem IIRC? Apart from the engine work, what turbo and injectors are fitted and was it re-mapped?


1996 Portofino 20vt & 2000 Pearl White Plus
1985½ & 2016 2017 Fiat 124 Spider + XF Sportbrake
Re: Help with compression results [Re: shawtek] #1621772
12/06/2018 15:03
12/06/2018 15:03
Joined: Mar 2006
Posts: 85
Northumberland
shawtek Offline OP
Club Member 1721
shawtek  Offline OP
Club Member 1721
Reaping the fruits

Joined: Mar 2006
Posts: 85
Northumberland
Hi Dave,

yeah, that was my thinking too but it looks like it happens.

It had a hybrid turbo but the seals went (still need to get it refurbed). I got a super spool off somebody on here and stuck that on. I think it still has standard injectors but don't know for certain... fuel regulator & was remapped after all the work was done. It also has aquamist and an Apexi boost controller fitted (always ran at whatever the lowest boost setting was).

One thing I didn't do was get it remapped or do anything boot-wise after fitted the lower rated turbo... starting to wonder if that has caused everything to go Pete Tong?


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