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Triumph Torque    Cars    2000/2500/2.5PI  ›  Compression test
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gilesdive
November 11, 2006, 1:00pm Report to Moderator


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Hi folks
Just want to pick your brains for a minute. On a 2500 engine (mine is a PI unit in a TR6, CR,  125 bhp version) roughly what should I expect if I put a compression tester on it?

Just cranking it over, I am getting between 70 and 90 psi. There is a bit of a spread of readings there, but do you think they are generally too low? I was advised by one chap they should be well into 3 figures - is this so? If that's the case, head off.

Thanks


White 1974 TR6 is "toy" car for evenings & weekends only.
Used to drive Spitfires as main transport, but have a eurobox for work these days.
Don't believe in putting the roof up - a bit of snow never hurt anyone! Get the Biggles jacket out

Location: West Yorkshire
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Nick Jones
November 11, 2006, 2:23pm Report to Moderator

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Sounds a bit low to me - I would have thought 140 - 180 ish/  Ideally to be equal within 10psi.

Are you doing this with throttle open or closed?  This can make a difference - should be open.

Putting around a table-spoonful of oil into each bore will temporarily improve the ring seal and help determine whether this is a valve or bore issue.

If the engine is an ex-US detox thing they have very low compression ratio so your readings may not be too far off what they should be.

Nick


Nick Jones
Somerset UK

Vitesse Mk 1.5 Convertible EFI, Survivor of RBRR 2008, HCR & 10CR 2009, HCR 2010, 10CR2011, HCR 2012, 10CR2013 & 10CR2015.
2.5 PI Saloon now EFI (PIe?), Engine rebuilt and running sweet.  Diff howling...... Survivor of HCR 2013 & 2014 Gone to live in Swansea

http://www.tengaston.plus.com
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gilesdive
November 11, 2006, 3:24pm Report to Moderator


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Ah, did it with throttle closed.
It is not an ex-USA car, it is to UK spec.
Fairly sure it's not piston rings/bores as harly any smoke when it was last running.

Bad news is I have taken back compression tester (only borrowed it) - but not sounding good is it?

Thanks for the quick answer though.


White 1974 TR6 is "toy" car for evenings & weekends only.
Used to drive Spitfires as main transport, but have a eurobox for work these days.
Don't believe in putting the roof up - a bit of snow never hurt anyone! Get the Biggles jacket out

Location: West Yorkshire
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davesideways
November 11, 2006, 7:24pm Report to Moderator
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gilesdive
November 13, 2006, 3:27pm Report to Moderator


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Thanks for those details. I have had to shell out for a guage as the one I borrowed is no longer available - will be able to check it with throttles open next weekend, at least I know what it should be.


White 1974 TR6 is "toy" car for evenings & weekends only.
Used to drive Spitfires as main transport, but have a eurobox for work these days.
Don't believe in putting the roof up - a bit of snow never hurt anyone! Get the Biggles jacket out

Location: West Yorkshire
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Richard B
November 13, 2006, 3:50pm Report to Moderator

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Good luck, also do a dry test followed by a wet test (add a drop of engine oil). I there is a significant improvement suspect Piston Rings. 


Surrey AO and Triumph Hoover, Location: Guildford - Surrey,
Spitfire 2.5PI - 1967 having surgery, PI Saloon - 1969, PI Estate - 1969 (to restore), Stag - 1971,
PI Saloon MkII - 1971(stalled project), Sold some cars!  

Daughters own: Herald 1500 1961, Herald 1500 Coupe 1962, Dolomite 1300 1976, Herald 13/60 Estate 1970
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Freebird
November 14, 2006, 6:06pm Report to Moderator


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Before I rebuilt my 2.5, the compression on number 1 was 7 bar - about 105 PSI with the throttle wide open, all the others were about 140 - 150 PSI. It had a CR of 8.5-1

Both top piston rings on No1 were stuck in their grooves, breaking up on pushing them past the big step in the bore (or broken already). A 20 thou rebore just about cleaned up the wear which was much the same in all bores - that's how bad it was. It didn,t actually smoke much even when cold, the oil control rings were all intact.

As Dave says 70-90 really doesn't sound right.

Glen.


'69 Vitesse Convertible 2500
'78 Spitfire 1500 - Gone to No1 son (only one actually) Joe
'80 Dolly Sprint - for sale on eBay.
'98 Jaguar XJ8 4.0 Sovereign LPG - daily driver!

'81 Laverda 3CL
'99 Triumph Sprint Sport 900


Location: Merstham, Surrey.
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JohnD
November 14, 2006, 8:55pm Report to Moderator


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Compression testers are NOT precision instruments!
So the absolute pressure shown by each tester may not compare, other than 'ball-park' .
Far more important than absolute pressure is that all cylinders should be the same.
Suspect any that aren't.
If the oil test doesn't improve pressure, then suspect the valves.

John


Serial Vitesse racer.

Old Blue.  1995-2001
Silverback. 2001-2007
SofS. 2007 - to date.

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gilesdive
November 26, 2006, 12:00pm Report to Moderator


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Been a slight delay in getting this done (illness / work) but finally did compression check with throttles fully open - yes, a big difference.
Lowest one was 165 psi and the highest about 175-180, that was without any oil in the bores.
Good news, this suggests valves and piston rings ok, don't need to pull the head off.
All I need now is to actually get it going!


White 1974 TR6 is "toy" car for evenings & weekends only.
Used to drive Spitfires as main transport, but have a eurobox for work these days.
Don't believe in putting the roof up - a bit of snow never hurt anyone! Get the Biggles jacket out

Location: West Yorkshire
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Nick Jones
November 26, 2006, 3:29pm Report to Moderator

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Posts: 8,677
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That sounds pretty good, especially if done cold.  Normally improve a bit when warm.

Nick


Nick Jones
Somerset UK

Vitesse Mk 1.5 Convertible EFI, Survivor of RBRR 2008, HCR & 10CR 2009, HCR 2010, 10CR2011, HCR 2012, 10CR2013 & 10CR2015.
2.5 PI Saloon now EFI (PIe?), Engine rebuilt and running sweet.  Diff howling...... Survivor of HCR 2013 & 2014 Gone to live in Swansea

http://www.tengaston.plus.com
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