Chimaera 400 Compression Readings
Discussion
Hi all
I've owned a Chimaera for an entire week now and I absolutely love the thing.
Always knew it needed the body coming off but while everything was together I did a compression test. Got around 185psi on 5 cylinders but three were a little sad: 150, 142 and 165ish. On adding oil to the cylinders, they all bumped up to 190.
From what I've read, this sounds like worn rings? Is it just a case of re-honing the block and fitting new rings?
Cheers!
James
I've owned a Chimaera for an entire week now and I absolutely love the thing.
Always knew it needed the body coming off but while everything was together I did a compression test. Got around 185psi on 5 cylinders but three were a little sad: 150, 142 and 165ish. On adding oil to the cylinders, they all bumped up to 190.
From what I've read, this sounds like worn rings? Is it just a case of re-honing the block and fitting new rings?
Cheers!
James
jjbradders said:
Hi all
I've owned a Chimaera for an entire week now and I absolutely love the thing.
Always knew it needed the body coming off but while everything was together I did a compression test. Got around 185psi on 5 cylinders but three were a little sad: 150, 142 and 165ish. On adding oil to the cylinders, they all bumped up to 190.
From what I've read, this sounds like worn rings? Is it just a case of re-honing the block and fitting new rings?
Cheers!
James
Should be but if your going to the trouble of removing engine it might be prudent to top hat liner the bores, re use your pistons with new rings and if your cam looks ok a fairly cheap build. Compressions pretty good and you must be fairly happy with that, I'm sure a hone and new rings gapped correctly should see you ok but 142 is looking low! I've owned a Chimaera for an entire week now and I absolutely love the thing.
Always knew it needed the body coming off but while everything was together I did a compression test. Got around 185psi on 5 cylinders but three were a little sad: 150, 142 and 165ish. On adding oil to the cylinders, they all bumped up to 190.
From what I've read, this sounds like worn rings? Is it just a case of re-honing the block and fitting new rings?
Cheers!
James
Others with more knowledge will confirm hopefully
Glad you like the car, their ace are they not
I'd be inclined to get a second opinion from one of the respected Tvr engine builders or someone who knows RV8 well.
Liners might not really be necessary if you can loose that loss of pressure via new rings unless you really want to rebuild the engine as it soon adds up. Would you be doing the engine work yourself because if your are then a full rebuilt engine could be say 2k maybe less depending on the state of your cam, rockers and oil pump gears etc. That would include getting the block top hat linered
You might have some carbon build up on a valve, or it's not fully seating so causing loss of pressure.
If the engines running well take it for an Italian tune, get it revvin, often oils up the cam lifters so quietens down valve train noise and can help clear deposits, try the compression test on the lower reading pots after and see what it says. You'll be surprised.
These engines usually sit at lowish revs, overfuelling and choking up. If it works it's a bit of a de coke and your idle might be smoother afterwards too. Spraying misted water into inlet tract can do a similar thing, you often notice on a piston that's had water entering the bore via a blown gasket or whatever that piston with be clean. De coked. I've never tried the water idea but I'm sure it works as a way to decoke the combustion chamber without pulling engine apart.
Not sure if I'd want to run it afterwards without replacing the engine oil so very much a personal decision.
I'm just wondering if it could be valve rather than bore issues causing pressure loss before assuming it's a bore or ring problem.
Try taking off the flame trap pipe and running engine if it's coming up through heads you might be getting some breathing there.
Have you got any exhaust smoke.
Liners might not really be necessary if you can loose that loss of pressure via new rings unless you really want to rebuild the engine as it soon adds up. Would you be doing the engine work yourself because if your are then a full rebuilt engine could be say 2k maybe less depending on the state of your cam, rockers and oil pump gears etc. That would include getting the block top hat linered
You might have some carbon build up on a valve, or it's not fully seating so causing loss of pressure.
If the engines running well take it for an Italian tune, get it revvin, often oils up the cam lifters so quietens down valve train noise and can help clear deposits, try the compression test on the lower reading pots after and see what it says. You'll be surprised.
These engines usually sit at lowish revs, overfuelling and choking up. If it works it's a bit of a de coke and your idle might be smoother afterwards too. Spraying misted water into inlet tract can do a similar thing, you often notice on a piston that's had water entering the bore via a blown gasket or whatever that piston with be clean. De coked. I've never tried the water idea but I'm sure it works as a way to decoke the combustion chamber without pulling engine apart.
Not sure if I'd want to run it afterwards without replacing the engine oil so very much a personal decision.
I'm just wondering if it could be valve rather than bore issues causing pressure loss before assuming it's a bore or ring problem.
Try taking off the flame trap pipe and running engine if it's coming up through heads you might be getting some breathing there.
Have you got any exhaust smoke.
Edited by Classic Chim 13.111 on Saturday 13th May 00:07
sparkythecat said:
I always understood that if the 'wet' compression readings ( ie.oil added to the bores) were better than the dry readings, then it was a bore or ring issue rather than any issue with the valves.
Yeah that was what I was thinking. Is it possible to remove the heads with the exhaust manifolds? Could check for leaking valves whilst I'm at it? It could be something as simple as a worn camshaft, valvetrain wear, head gaskets etc. I'd expect the rings to have worn by a similar amount.
Does the car drive well without oil or coolant issues? If so, I'd be inclined to leave it as it is for now so as to enjoy it. If you want to do a rebuild then that could happen over the winter.
Incidentally, when I do a test it's with the throttle fully open. I have heard of people not doing it this way.
Does the car drive well without oil or coolant issues? If so, I'd be inclined to leave it as it is for now so as to enjoy it. If you want to do a rebuild then that could happen over the winter.
Incidentally, when I do a test it's with the throttle fully open. I have heard of people not doing it this way.
Yeah I had reservations about the cam, might have to get a DTI and measure the lift. Its at 72k miles and no evidence of a new one being fitted.
I wish I could leave it to the winter! But it's out of tax, I need to have a think of very lenient insurers and I'd planned to strip it now anyway.
Id rather it was a worn cam really, good excuse to go for an MC1 I think ;-)
I wish I could leave it to the winter! But it's out of tax, I need to have a think of very lenient insurers and I'd planned to strip it now anyway.
Id rather it was a worn cam really, good excuse to go for an MC1 I think ;-)
sparkythecat said:
If the cam or valves were the issue, then the readings wouldn't improve and equalise just by putting a drop of oil in the cylinders, as the OP has reported happening.
Fair point. OP cam change isn't too daunting if you take your time. V8 developments have a nice write up on the procedure.
I was between mc1 and stealth cam. Opted for stealth and very happy. Swap was at 54k miles and the original was excessively worn so IF it doesn't fix the problem it's time the original was binned anyway.
But retest with a warm engine and WOT
Thanks for the replies all, been really useful!
Chimp871 - Is that possible on a Chimaera without burning yourself thoroughly? Also don't want to melt the tester but if it's been done before I'll have a crack at it.
QBee - Sheffield, so good for chassis! There's an engine shop near me that have done an MX5 block and Fiat X1/9 for me before. Did a really good job so if a hone is needed, I'll lob it their way.
Sardonicus - At this rate I'll strip it all anyway so hopefully I'll be able to spot that?
You guys really are a mine of knowledge
Chimp871 - Is that possible on a Chimaera without burning yourself thoroughly? Also don't want to melt the tester but if it's been done before I'll have a crack at it.
QBee - Sheffield, so good for chassis! There's an engine shop near me that have done an MX5 block and Fiat X1/9 for me before. Did a really good job so if a hone is needed, I'll lob it their way.
Sardonicus - At this rate I'll strip it all anyway so hopefully I'll be able to spot that?
You guys really are a mine of knowledge
sparkythecat said:
If the cam or valves were the issue, then the readings wouldn't improve and equalise just by putting a drop of oil in the cylinders, as the OP has reported happening.
This is a logical response but lobbing some oil in the cylinders isn't a scientific approach and neither was it measured. The test could be repeated a few times to see if the results are repeated. That would be a way forward and use the same amount of oil per cylinder.Before dismantling an engine I'd prefer to examine the easy bits especially if an upgrade's on the cards at the same time :-)
jjbradders said:
Richard showed me round a couple of months ago, great guy so I might pop down.
And if I do upgrade it, it'll only be mild! I know it's the least powerful and all that, but I'm not experienced or old enough to muck around with any more I think
The 400 is a more than adequate road car. It is a thing of beauty, loved by the great British public and other car owners. It is also a nice revving engine and less prone to expensive problems, as it is a good solid Range Rover design. And if I do upgrade it, it'll only be mild! I know it's the least powerful and all that, but I'm not experienced or old enough to muck around with any more I think
The bigger engines and modified engines only serve three purposes IMHO:
1. To improve your track driving experience
2. To cause greater wallet damage, on upgrades, repairs and fuel consumption
3. To allow you more opportunity to wave your willy at shows etc.....when the cars are standing still, parked in a neat row. Seems slightly odd.......
and on a cold day it can cause frostbite in the perpendiculars. 
Enjoy your lovely car for what it is and be proud of it.
jjbradders said:
And if I do upgrade it, it'll only be mild! I know it's the least powerful and all that, but I'm not experienced or old enough to muck around with any more I think
Post a picture of your engine bay on here now.
Then you can come back in a couple of years, post another one, and we can all roll about on the floor laughing and say, "really?" A TVR is a thing of beauty, and an opportunity to modify. Mine started out just like yours, as a standard Starmist Blue 400, 5 years ago. Since then it has been a 500, and now looks like this under there.....and, yes, I do do track days
And yes, my wallet is empty
That looks very nice QBee, love the plenum badge 
Just got the car up to temp and did another compression test (I'll feel my hand again in a few days I'm sure) and very similar again eg. 150 VS 145 psi cold at WOT.
Not looking good I reckon... Its missing irregularly when up to temp as well. What should next plan of action be? Pull the heads off to check for leaking valves or if it's the bores, go about sorting that?
Just got the car up to temp and did another compression test (I'll feel my hand again in a few days I'm sure) and very similar again eg. 150 VS 145 psi cold at WOT.
Not looking good I reckon... Its missing irregularly when up to temp as well. What should next plan of action be? Pull the heads off to check for leaking valves or if it's the bores, go about sorting that?
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