Compression Test
Discussion
The old girl has now done over 100,000 miles and although it runs smoothly
enough it has never performed as well as I expected.
I thought I'd do a compression test at the weekend.
I got the following values in psi:
90, 90, 95, 100, 100, 110, 118, 118
Is this about right for an engine of this mileage or do I need to save up some pennies for a re-build?
I haven't a clue whether these are good or bad values so any feedback would be appreciated
Cheers y'all
Dave Meredith
enough it has never performed as well as I expected.
I thought I'd do a compression test at the weekend.
I got the following values in psi:
90, 90, 95, 100, 100, 110, 118, 118
Is this about right for an engine of this mileage or do I need to save up some pennies for a re-build?
I haven't a clue whether these are good or bad values so any feedback would be appreciated
Cheers y'all
Dave Meredith
Running a "wet" compression test lets you differentiate between valve wear and piston ring wear - as well as giving a better overall impression.
If the compression improves between a "dry" and "wet" test then your valves are probably OK and your rings/bores are worn, otherwise it's the valves.
If it shows worn valves then you might want to risk a top-end rebuild only, depending on your attitude to taking the engine out.
The Rover manual says: -
All readings should be within 20 lbf/in (1.4 bar) of each other and should all be above 150 lbf/in (10.3 bar). This is for the 9.75 :1 engine.
Russ
But the important question is "does it feel allright?" - then leave it alone!
If the compression improves between a "dry" and "wet" test then your valves are probably OK and your rings/bores are worn, otherwise it's the valves.
If it shows worn valves then you might want to risk a top-end rebuild only, depending on your attitude to taking the engine out.
The Rover manual says: -
All readings should be within 20 lbf/in (1.4 bar) of each other and should all be above 150 lbf/in (10.3 bar). This is for the 9.75 :1 engine.
Russ
But the important question is "does it feel allright?" - then leave it alone!
Thanks for the feedback Chaps.
In 2008 the wife spent an obscene amount of money on some bridge work when one or two of her teeth were beyond saving. I did
at one time mention the word 'denture' but when her friends started calling me Timmy-tight-ass I realised I wasn't going to
get very far with that approach. I bided my time.
With this in mind I went to my local spray shop for a quote in 2009 and by some quirk of fortune the quote was exactly what my
better half had spent on her teeth. I was then able to go back to the missus and claim that since my teeth were fine I wanted to get
the TVR re-sprayed with the little windfall that had so conveniently arrived that spring. After a bit of huffing and puffing, a hang-dog expression and a day of the sulks the TVR was duly re-sprayed (does everyone have to go through this little pantomime?)
Well this year was a landmark birthday for 'er indoors and 2010 has been one long celebration. We have had once-in-a-lifetime
holidays, an open top bus ride, jewellery from the outer hebrides - you name it - she's had it. She say's "you can't take it with you can you?". Well I can assure you, there's no chance of me taking any money with me into the wooden box if we have another
year like this one. Once again I bit my lip and bided my time.
Another little windfall may arrive next spring and I may once again be in a position to lavish more money on the real love of my
life. Negotiations are at an early stage and I have been wandering around the house carrying a compression test gauge while nonchalently whistling in an absent minded sort of way. Of course the inevitable questions followed and I have been able to tell
her now with some confidence, and the look of a doctor who's got to give you same bad news, that "the old engine is getting a bit tired love". Of course she replies: "It's about time you spent more time with me rather than polishing that noisy heap you call a sports car". That's her opening gambit so like I say, negotiations are at an early stage.
I gues what I'm trying to say is that although the engine may last a few more years, the money is available now. It's not always about common sense is it? After all, you can't take it with you can you?
In 2008 the wife spent an obscene amount of money on some bridge work when one or two of her teeth were beyond saving. I did
at one time mention the word 'denture' but when her friends started calling me Timmy-tight-ass I realised I wasn't going to
get very far with that approach. I bided my time.
With this in mind I went to my local spray shop for a quote in 2009 and by some quirk of fortune the quote was exactly what my
better half had spent on her teeth. I was then able to go back to the missus and claim that since my teeth were fine I wanted to get
the TVR re-sprayed with the little windfall that had so conveniently arrived that spring. After a bit of huffing and puffing, a hang-dog expression and a day of the sulks the TVR was duly re-sprayed (does everyone have to go through this little pantomime?)
Well this year was a landmark birthday for 'er indoors and 2010 has been one long celebration. We have had once-in-a-lifetime
holidays, an open top bus ride, jewellery from the outer hebrides - you name it - she's had it. She say's "you can't take it with you can you?". Well I can assure you, there's no chance of me taking any money with me into the wooden box if we have another
year like this one. Once again I bit my lip and bided my time.
Another little windfall may arrive next spring and I may once again be in a position to lavish more money on the real love of my
life. Negotiations are at an early stage and I have been wandering around the house carrying a compression test gauge while nonchalently whistling in an absent minded sort of way. Of course the inevitable questions followed and I have been able to tell
her now with some confidence, and the look of a doctor who's got to give you same bad news, that "the old engine is getting a bit tired love". Of course she replies: "It's about time you spent more time with me rather than polishing that noisy heap you call a sports car". That's her opening gambit so like I say, negotiations are at an early stage.
I gues what I'm trying to say is that although the engine may last a few more years, the money is available now. It's not always about common sense is it? After all, you can't take it with you can you?
Nice 4.6 in there now then 
Just tell her it's going in for a service. "yes love, bout £50 this time"The test was done on a cold engine without any oil squirted down the bores.
I've had the car 4 years and in that time its done about 8000 miles, so it has always been a high
mileage engine in my ownership. I had a rolling road test doen a year ago and it produced about 110bhp
at the wheels. This combined with my compression test values seem to suggest that the old girl is getting
a bit tired. I'm the 14th owner of the car which works out at about 18months per owner. I get the feel
that each owner has had a mad thrash and passed it on.
Yes I suppose I could squirt some oil in the bores, get some better figures and rush back to the missus
with the news that everything will be alright for a few more years. She will just waste the money on a new
three peice suite and a kitchen table.
I'm going to have a chat to my local engine re-conditioner in a week or so. I'll let you know how I get on.
I've added up the cost of the wife's year of celebration (inculding the open top bus Adam) so I know my available budget!
cheers chaps!
Dave
I've had the car 4 years and in that time its done about 8000 miles, so it has always been a high
mileage engine in my ownership. I had a rolling road test doen a year ago and it produced about 110bhp
at the wheels. This combined with my compression test values seem to suggest that the old girl is getting
a bit tired. I'm the 14th owner of the car which works out at about 18months per owner. I get the feel
that each owner has had a mad thrash and passed it on.
Yes I suppose I could squirt some oil in the bores, get some better figures and rush back to the missus
with the news that everything will be alright for a few more years. She will just waste the money on a new
three peice suite and a kitchen table.
I'm going to have a chat to my local engine re-conditioner in a week or so. I'll let you know how I get on.
I've added up the cost of the wife's year of celebration (inculding the open top bus Adam) so I know my available budget!
cheers chaps!
Dave
Dave,
http://www.pumaracing.co.uk/comp.htm
Have a read of engine guru Dave Baker's guidance on compression testing. You should be doing it ith a hot engine, at wide open throttle. As an approximation, you can expect a healthy engine to give results of around 17 to 20 times the CR. So, if the 400se engine really does have a 10.5:1 CR that TVR claimed, it would give around 178 - 210psi compression.
By way of comparision, I tested my own 400se earlierr this year. OK, it's actually a modified 4.3, with a CR of around 9.5:1, but the readings I got were all in the range of 195 - 210 psi.
I think it would be worth you re-doing the test per Dave's guidance. I'm also a bit puuzzled by your RR figure of 110 bhp - do you mean 210?
One likely problem is the camshaft. Is it the original with 100K miles on it? It's not unknown for cams to be worn enough to require replacement after 60K miles, depending on how it's been used (or abused) and the oil quality, changes etc.
7.
http://www.pumaracing.co.uk/comp.htm
Have a read of engine guru Dave Baker's guidance on compression testing. You should be doing it ith a hot engine, at wide open throttle. As an approximation, you can expect a healthy engine to give results of around 17 to 20 times the CR. So, if the 400se engine really does have a 10.5:1 CR that TVR claimed, it would give around 178 - 210psi compression.
By way of comparision, I tested my own 400se earlierr this year. OK, it's actually a modified 4.3, with a CR of around 9.5:1, but the readings I got were all in the range of 195 - 210 psi.
I think it would be worth you re-doing the test per Dave's guidance. I'm also a bit puuzzled by your RR figure of 110 bhp - do you mean 210?
One likely problem is the camshaft. Is it the original with 100K miles on it? It's not unknown for cams to be worn enough to require replacement after 60K miles, depending on how it's been used (or abused) and the oil quality, changes etc.
7.
Edited by Number 7 on Wednesday 1st September 08:29
Edited by Number 7 on Wednesday 1st September 08:33
Hmm - not so good then - I had a bad bus experience in Barbados, chap drove too close to a tree, shattered the wing mirror and a 3 inch shard came into the bus and hit my left eyeball. Luckily just a scratch on the lens.
Anyhoo, yes that's the problem with the compression test, re-do it hot, then again with oil. It's respectable for a cold engine.
Anyhoo, yes that's the problem with the compression test, re-do it hot, then again with oil. It's respectable for a cold engine.
Number 7
In response to you query about the RR figure of 110bhp. I've just looked at the diagram (I'll post it on here if someone can
show me how) and the figure is actually about 105bhp
I took it in for a RR test because it was pinking badly. They backed off the ignition from about 8deg to 3deg which solved the problem. Obviously this has affected the bhp reading but I would still expect to get more than 105bhp! The engine is a 3.5 V8 in
its standard form. According to the handbook this should chuck out around 197bhp at the flywheel.
Dave
In response to you query about the RR figure of 110bhp. I've just looked at the diagram (I'll post it on here if someone can
show me how) and the figure is actually about 105bhp
I took it in for a RR test because it was pinking badly. They backed off the ignition from about 8deg to 3deg which solved the problem. Obviously this has affected the bhp reading but I would still expect to get more than 105bhp! The engine is a 3.5 V8 in
its standard form. According to the handbook this should chuck out around 197bhp at the flywheel.
Dave
Dave Meredith said:
Number 7
In response to you query about the RR figure of 110bhp. I've just looked at the diagram (I'll post it on here if someone can
show me how) and the figure is actually about 105bhp
I took it in for a RR test because it was pinking badly. They backed off the ignition from about 8deg to 3deg which solved the problem. Obviously this has affected the bhp reading but I would still expect to get more than 105bhp! The engine is a 3.5 V8 in
its standard form. According to the handbook this should chuck out around 197bhp at the flywheel.
Dave
For some reason I thought your car was a 400, so ignore the estimates for compression values. The 350 should have a cr of 9.75:1, so a healthy engine should give around 165 - 195 psi. You need to re-do the test. Our of interest, do you run on ordinary or super unleaded? If you want to post a picture, you need to use a hosting service like Photobucket. Basically you create an account (free) and upload the picture from your PC to the host service, and then copy the image link into a message here. I think there's a sticky about this somewhere here. Did you also get the AFR graph from the RR session?In response to you query about the RR figure of 110bhp. I've just looked at the diagram (I'll post it on here if someone can
show me how) and the figure is actually about 105bhp
I took it in for a RR test because it was pinking badly. They backed off the ignition from about 8deg to 3deg which solved the problem. Obviously this has affected the bhp reading but I would still expect to get more than 105bhp! The engine is a 3.5 V8 in
its standard form. According to the handbook this should chuck out around 197bhp at the flywheel.
Dave
7.
Dave Meredith said:
The old girl has now done over 100,000 miles and although it runs smoothly
enough it has never performed as well as I expected.
I thought I'd do a compression test at the weekend.
I got the following values in psi:
90, 90, 95, 100, 100, 110, 118, 118
25% variation is very high. A 4.6 is starting to sound good. Exhaust OK?enough it has never performed as well as I expected.
I thought I'd do a compression test at the weekend.
I got the following values in psi:
90, 90, 95, 100, 100, 110, 118, 118
Dave,
I've just realised my email address in my profile was wrong. Try re-sending and I'll put the graphs up on Photobucket. Using ordinary unleaded may be one reason it wss pinking. The 8 deg. btdc was from an era when octane levels were higher than unleaded. I always used to run our 350 (and the 400) on super.
7.
I've just realised my email address in my profile was wrong. Try re-sending and I'll put the graphs up on Photobucket. Using ordinary unleaded may be one reason it wss pinking. The 8 deg. btdc was from an era when octane levels were higher than unleaded. I always used to run our 350 (and the 400) on super.
7.
Here is the graph. As I've told Dave, I've never seen this format before, with what appears to be a time rather than engine speed along the horizontal axis. The only thing that I would say is that the AFR is massively lean at the top end, which is obviously not helping things. The graph itself I can't really work out though. Any ideas from anyone, other than to re-do the comp tests dry and wet with a hot engine, as this won't cost anything, and it should give a better idea of engine condition.
The engine speed row in the table at the bottom reads 2,482, 5,385 and 4,282
7.
The engine speed row in the table at the bottom reads 2,482, 5,385 and 4,282
7.
Edited by Number 7 on Thursday 2nd September 18:04
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