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Nico
Guest
Turns out the mules not just low one cylinder. Its low on all 5! Besides cam timing pehaps having slipped, what else could be causing this?
Currently reading:
Q.Causes of low compression please??
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Anonymous
Guest
knackered engine - bores and piston rings, valve seats.
OP
OP
Nico
Guest
valve seats could be ported angled couldn't they
and piston rings replaced, but this would be an 'engine out' wouldn't it?
and piston rings replaced, but this would be an 'engine out' wouldn't it?
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Ash
Guest
new set of piston rings, have the bore on each cylinder re-honed replace the valve stem seals, and re grind the valves and it will sort it. if your cams arnt closing the valves properly it could cause it. also your valve springs could have been weakened by the extra stres of the lumpier cams.
it may be that ur timing is just out a bit. a set of adjustable pullies would help you get it set more acuratly.
personally if they are all about the same i wouldnt worry if the car is running fine. if one or two are lower than the others then you have issues.
who measured the compression and are they compairing it to the fiat specs? remember your engine has had a bit of tinkering so i wouldnt follow the fiat specs as the bible of all knowledge.
remember the compression also relies on the atmospheric pressure of the air going in to the engine.
Anything With Tits or Wheels Will Cost You MONEY!!
it may be that ur timing is just out a bit. a set of adjustable pullies would help you get it set more acuratly.
personally if they are all about the same i wouldnt worry if the car is running fine. if one or two are lower than the others then you have issues.
who measured the compression and are they compairing it to the fiat specs? remember your engine has had a bit of tinkering so i wouldnt follow the fiat specs as the bible of all knowledge.
remember the compression also relies on the atmospheric pressure of the air going in to the engine.
Anything With Tits or Wheels Will Cost You MONEY!!
J
Joske
Guest
As above, my mates Astra GSi had the same problem.
It can be any of the below aswell.
Cracked head
Blown piston
Cracked Block
Blown head gasket
Broken valve component - spring, cracked seat, bent valve, bad lifter
Maybe your putting too much pressure on your mule with these modifications. Your seriously reducing its engine life with the increases you've gain.
It can be any of the below aswell.
Cracked head
Blown piston
Cracked Block
Blown head gasket
Broken valve component - spring, cracked seat, bent valve, bad lifter
Maybe your putting too much pressure on your mule with these modifications. Your seriously reducing its engine life with the increases you've gain.
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Tom
Guest
How low is low? What are all 5 numbers?
Slipped cam timing would affect ALL the cyls, not just one.
There are some quick and simple tests you can do to determine whats causing it.
Slipped cam timing would affect ALL the cyls, not just one.
There are some quick and simple tests you can do to determine whats causing it.
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Tom
Guest
Also note that longer duration cams such as the C&Bs will give lower figures.
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cynic-al
Guest
or you forgot to put the spark plugs in 
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Anonymous
Guest
Cheers for the replies guys.
The drop off in power was noticeable some months ago now, but its only after the exhaust was fixed and the mass mater has been replaced, that we did a compression test since even the mechanic said its not as quick as it used to be.
My mechanics suggested I let em have it back when next convenient, for them to investigate further, but for my own benefit, whilst we have a list of potential culprits, how do they go about testing for these faults??
The drop off in power was noticeable some months ago now, but its only after the exhaust was fixed and the mass mater has been replaced, that we did a compression test since even the mechanic said its not as quick as it used to be.
My mechanics suggested I let em have it back when next convenient, for them to investigate further, but for my own benefit, whilst we have a list of potential culprits, how do they go about testing for these faults??
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Tom
Guest
Tell us what the compression numbers actually are. 'low' is not very descriptive
Also a leakdown test is FARRRRR more accurate as it removes factors like long duration cams.
Also a leakdown test is FARRRRR more accurate as it removes factors like long duration cams.
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Anonymous
Guest
If you have fitted after market cams then the on the compression stroke alot could be disappearing out the exhaust if the exhaust valve is opening too early due to the overlap of the cams being different. As Tom has hinted the engine amy never develope "high" compression which in itself isn't a bad thing Anyway some engines have a lower compression - forced induction supercharged or turbo typically 7.5 to 1.
If yours is normally aspirated then typically anywhere from 150-180psi right up 200+. But get yourself a compression tester they are not that expensive given the cost of engine work. £20 I think for a Gunsons one. Do a test with the engine cold and then at normal working temp on ALL cylinders. Take all the plugs out and crank over with just the tester in place in the head. Then tell us what you find. Also the characteristics of the cams if they are non standard.
If yours is normally aspirated then typically anywhere from 150-180psi right up 200+. But get yourself a compression tester they are not that expensive given the cost of engine work. £20 I think for a Gunsons one. Do a test with the engine cold and then at normal working temp on ALL cylinders. Take all the plugs out and crank over with just the tester in place in the head. Then tell us what you find. Also the characteristics of the cams if they are non standard.
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Paul R
Guest
its normally piston rings that cause low compression but as said it can be many many thing, normally piston rings equal one or two dropping, they dont tend to wear so perfectly.
if you need a new engine (cheaper then rebuild) i have a hgt lump, swap the heads over and away you go
hope you dont need a new engine though
Paul R
if you need a new engine (cheaper then rebuild) i have a hgt lump, swap the heads over and away you go
hope you dont need a new engine though
Paul R
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nico
Guest
Compression I would say has been getting steadily worse for about 6 months. Then again what with blowing exhaust and new mass meter I put up with for months too, I could be wrong. I did notice the drop most noticeably within the space of a week before the exhaust started blowing I reckon. Either way, the mule was running great with the cams for ages, but something somewhere has gone wrong since.
Just rang the garage and they say they're all down around 90 stead of 150!!!!
As for engine swops Paul, I have a friend who's willing (and by all counts - capable too) to do the 20VT swop with engine, parts and new management system to boot, for 2350. I don't want it though. Would rather restore the mule to full kick.
Just rang the garage and they say they're all down around 90 stead of 150!!!!
As for engine swops Paul, I have a friend who's willing (and by all counts - capable too) to do the 20VT swop with engine, parts and new management system to boot, for 2350. I don't want it though. Would rather restore the mule to full kick.
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Tom
Guest
OK, 90 is getting low
Either do a leakdown test or squirt a few CCs of engine oil into each bore in turn and redo the test. If the numbers jump up after adding the oil then your bores/rings are shot.
If there is no change then its a prob with the cyl head assembly. Although its unlikely badly seated valves would give the same result on all cyls.
Either do a leakdown test or squirt a few CCs of engine oil into each bore in turn and redo the test. If the numbers jump up after adding the oil then your bores/rings are shot.
If there is no change then its a prob with the cyl head assembly. Although its unlikely badly seated valves would give the same result on all cyls.
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nico
Guest
Cheers for the insights Tom
How do they actually perform a leakdown test?
I'd imagine the rings are lest costly than the option of having the cylindars re-bored!? If indeed this was necessary, would merely replacing the rings with a larger bore be sufficient, or would that be pistons too?
Either way, is it engine out to get at em?
If the faults elsewhere, where might it lie in the head assembly if not associated with the valve seats. Could it just be a gasket?
How do they actually perform a leakdown test?
I'd imagine the rings are lest costly than the option of having the cylindars re-bored!? If indeed this was necessary, would merely replacing the rings with a larger bore be sufficient, or would that be pistons too?
Either way, is it engine out to get at em?
If the faults elsewhere, where might it lie in the head assembly if not associated with the valve seats. Could it just be a gasket?
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Tom
Guest
If the results are consistent then its unlikely to be gasket, cracked head etc.. When that happens you get wildly different numbers.
I've seen engines with 150, 50, 50 and zero as compression values, it had a holes piston on the zero cyl
If the rings are gone the bores are most likely shot, you can just re-ring but its a short term option IMO and if there is a lip in the bore then its pretty pointless.
Either way you need to find the cause and fix it or it will happen again.
I've seen engines with 150, 50, 50 and zero as compression values, it had a holes piston on the zero cyl
If the rings are gone the bores are most likely shot, you can just re-ring but its a short term option IMO and if there is a lip in the bore then its pretty pointless.
Either way you need to find the cause and fix it or it will happen again.
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nico
Guest
Oil pump / lack of oil could have caused the wear to the bores then.
Assuming I can find what caused it, it is perfectly feasible for me then just to replace the rings, or if I do need to re-bore, is that cylidars too, and just how costly perhaps?? (I know you don't have a crystal ball, but are we talking enine out and £1000+??)
Assuming I can find what caused it, it is perfectly feasible for me then just to replace the rings, or if I do need to re-bore, is that cylidars too, and just how costly perhaps?? (I know you don't have a crystal ball, but are we talking enine out and £1000+??)
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Tom
Guest
More likely cause is bore wash from too much petrol.
Lack of oil will screw the cams, big ends and mains as well as the bores.
Ideally if the bores are shot you would rebore to the next oversize and get a set of oversize pistons & rings. The majority of the cost is taking the engine to bits.
Lack of oil will screw the cams, big ends and mains as well as the bores.
Ideally if the bores are shot you would rebore to the next oversize and get a set of oversize pistons & rings. The majority of the cost is taking the engine to bits.
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nico
Guest
Not really wanting to consider worst case scenario, but if it tunrs out to be the case, anyone know any good engineers for such a task??
Plus potential suppliers for the pistons etc?
Plus potential suppliers for the pistons etc?
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Tom
Guest
Confirm the fault before you worry about it
I think Fiat might sell oversized pistons. A custom set would be mega ££ and coupe turbo ones would not give you the right compression.
I think Fiat might sell oversized pistons. A custom set would be mega ££ and coupe turbo ones would not give you the right compression.