Hi,
I was going to post this under the 2500 running on thread but didn't want to go off track. In an effort to solve my erratic idling and running on issues I have recently noticed slight fuming from the rocker cover. (My TR6 produces barely detectable crankcase fumes). Yesterday I took some compression figures (hot engine with open throttle and all plugs removed). They were...
1 - 180 PSI
2 - 180 PSI
3 - 165 PSI
4 - 180 PSI
5 - 180 PSI
6 - 185 PSI
Dropping some oil into the bore of no 3 took the reading up to 190 PSI so I'm guessing that theres a problem with this cylinder. Thinking about it, the last time I had the head off (decoke to stop pinking) I noticed some score marks in the bore of one of the middle cylinders but I took no notice of this at the time - I'm guessing that this was no3....
Is this anything to worry about or do I need to pull the engine out before it goes pop. I'm asking this because I have been offered a volvo t5 estate for just a few quid by a colleague at work... I would need another car if I'm going to have to rebuild the lump in the saloon...
Regards
James
compression test
-
Mike Stevens
- Site Admin
- Posts: 3649
- Joined: Mon May 08, 2006 9:50 pm
- Location: South Oxfordshire, UK
Re: compression test
Hi James,
On the face of it, these figures would not normally cause me any concern. Obviously there is an issue with No3 and your tests point to the rings. This is likely to cause blow-by and an increased crankcase pressure - hence the slight fuming (probably!). However, I wouldn't have thought this would cause erratic idle or run-on.
Is this a PI or carb engine? With these PSI figures I would expect it to be a PI as the carb CR is somewhat lower. But, if you have run-on it's unlikely to be a PI. Where I was going is that just about anything wrong with the engine has a knock-on effect on manifold depression which then effects the fuel metering on a PI.
At the end of the day, I would not expect this slight drop in compression pressure in No3 to 'make the engine go pop'. I would have thought that the effect is more likely to be rough idle etc, but it's only a drop of 8% on 180 PSI, not exactly huge!
Cheers,
Mike.
On the face of it, these figures would not normally cause me any concern. Obviously there is an issue with No3 and your tests point to the rings. This is likely to cause blow-by and an increased crankcase pressure - hence the slight fuming (probably!). However, I wouldn't have thought this would cause erratic idle or run-on.
Is this a PI or carb engine? With these PSI figures I would expect it to be a PI as the carb CR is somewhat lower. But, if you have run-on it's unlikely to be a PI. Where I was going is that just about anything wrong with the engine has a knock-on effect on manifold depression which then effects the fuel metering on a PI.
At the end of the day, I would not expect this slight drop in compression pressure in No3 to 'make the engine go pop'. I would have thought that the effect is more likely to be rough idle etc, but it's only a drop of 8% on 180 PSI, not exactly huge!
Cheers,
Mike.
(South Oxfordshire)
Register Member No 0355
1971 2.5PI Saloon Sapphire blue
1973 2.5PI Saloon rust some Honeysuckle
1973 Stag French blue
(1949 LandRover which is now back to its original light green!)
Register Member No 0355
1971 2.5PI Saloon Sapphire blue
1973 2.5PI Saloon rust some Honeysuckle
1973 Stag French blue
(1949 LandRover which is now back to its original light green!)
Re: compression test
Hi,
Thanks for the positive response!
The car is running twin hs6 carbs with a Witor cam (dynoed at 139 bhp). The head has been skimmed hence the higher pressures. I use the car for business and spend quite alot of time on motorways (though I do stick to the speed limit as I only get 24p per mile!) - hence my concern about the engine going pop. I have fitted an anti run on valve but this doesn't stop the running-on... I have also tried to lower the idle speed to prevent running on but because the tickover speed is so variable stalling was sometimes a problem.
I will try bypassing the breather pipes to the carbs - this may improve matters. I have a spare oil catch tank....
Regards
James
Thanks for the positive response!
The car is running twin hs6 carbs with a Witor cam (dynoed at 139 bhp). The head has been skimmed hence the higher pressures. I use the car for business and spend quite alot of time on motorways (though I do stick to the speed limit as I only get 24p per mile!) - hence my concern about the engine going pop. I have fitted an anti run on valve but this doesn't stop the running-on... I have also tried to lower the idle speed to prevent running on but because the tickover speed is so variable stalling was sometimes a problem.
I will try bypassing the breather pipes to the carbs - this may improve matters. I have a spare oil catch tank....
Regards
James
Re: compression test
Hello James,
I agree with Mike, I would not be that concerned, but would continue to monitor the pressures.
I think that removing the breathers from the carburettors and just venting to a catch tank is a good idea. It is possible that those fumes could be the cause of your running on, but don't hold your breath.
You mention the head has been skimmed, do you know if the sharp edge, (which machining the face will give) around the combustion chambers was removed? THis is another possible cause of running on?
Alec
I agree with Mike, I would not be that concerned, but would continue to monitor the pressures.
I think that removing the breathers from the carburettors and just venting to a catch tank is a good idea. It is possible that those fumes could be the cause of your running on, but don't hold your breath.
You mention the head has been skimmed, do you know if the sharp edge, (which machining the face will give) around the combustion chambers was removed? THis is another possible cause of running on?
Alec
0465
MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration, nearing completion.)
MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration, nearing completion.)
Re: compression test
Hi,
I'll give the catch tank a try - this can only improve the idle. When the head was skimmed there was a bad edge (sharp enough to cut a finger) which I cleaned up with a stone in the dremel however I can't remember whether I just took the rough edge off (probably the case) or smothed/radiused the edge. I think I will take the head off when I get chance and check this out.
Regards
James
I'll give the catch tank a try - this can only improve the idle. When the head was skimmed there was a bad edge (sharp enough to cut a finger) which I cleaned up with a stone in the dremel however I can't remember whether I just took the rough edge off (probably the case) or smothed/radiused the edge. I think I will take the head off when I get chance and check this out.
Regards
James
-
Mike Stevens
- Site Admin
- Posts: 3649
- Joined: Mon May 08, 2006 9:50 pm
- Location: South Oxfordshire, UK
Re: compression test
Hi James,
I wonder what plugs you are using? Having had the head skimmed, you may now want to run with cooler plugs. They could be getting a bit hot and causing the run-on. Mind you, if that was the case, I'd expect pinking too. Maybe.
I still think running a bit richer may help, this will help to 'cool' it all in there too, so maybe indicating something is glowing a bit!
My 2000 has a 2500S head skimmed to give me 9.5:1 and I'm also using HS6s. Enrichening the mixture a bit (it was all done by 'ear') seems to have helped. I'm still running with standard plugs though. Maybe some cooler ones will help even more.
Good luck!
Cheers,
Mike.
I wonder what plugs you are using? Having had the head skimmed, you may now want to run with cooler plugs. They could be getting a bit hot and causing the run-on. Mind you, if that was the case, I'd expect pinking too. Maybe.
I still think running a bit richer may help, this will help to 'cool' it all in there too, so maybe indicating something is glowing a bit!
My 2000 has a 2500S head skimmed to give me 9.5:1 and I'm also using HS6s. Enrichening the mixture a bit (it was all done by 'ear') seems to have helped. I'm still running with standard plugs though. Maybe some cooler ones will help even more.
Good luck!
Cheers,
Mike.
(South Oxfordshire)
Register Member No 0355
1971 2.5PI Saloon Sapphire blue
1973 2.5PI Saloon rust some Honeysuckle
1973 Stag French blue
(1949 LandRover which is now back to its original light green!)
Register Member No 0355
1971 2.5PI Saloon Sapphire blue
1973 2.5PI Saloon rust some Honeysuckle
1973 Stag French blue
(1949 LandRover which is now back to its original light green!)
Re: compression test
Hi,
I already have cooler plugs fitted... Today I have connected the breather to the rocker cover - the carb pipes are now connected to the anti-run on valve so I'll monitor how the car performes and update you. Not sure whether the fumes coming from the breather filter are going to intrude but we'll see. I wouldnt expect any fumes if the engine was OK.
Regards
James
I already have cooler plugs fitted... Today I have connected the breather to the rocker cover - the carb pipes are now connected to the anti-run on valve so I'll monitor how the car performes and update you. Not sure whether the fumes coming from the breather filter are going to intrude but we'll see. I wouldnt expect any fumes if the engine was OK.
Regards
James
Re: compression test
Hi,
Just to let you know the car is idling more smoothly (and consistently) now that the engine is breathing to an oil catch tank. Unfortunately the fumes from this are rather unpleasanst - especially after a long run then being stuck at the M6/M5 junction as I was last night. 'Running on' has reduced though still occurs (in spite of the solenoid valve being fitted). I have also retarded the ignition but the engine still pinks in 3rd/4th once warmed up. Looks like I'll be whipping the head off once the weather has warmed a little. (I dont mind working in the cold but my backup car is a TR6 and I dont want it to dissolve before my eyes!).
Regards
James
Just to let you know the car is idling more smoothly (and consistently) now that the engine is breathing to an oil catch tank. Unfortunately the fumes from this are rather unpleasanst - especially after a long run then being stuck at the M6/M5 junction as I was last night. 'Running on' has reduced though still occurs (in spite of the solenoid valve being fitted). I have also retarded the ignition but the engine still pinks in 3rd/4th once warmed up. Looks like I'll be whipping the head off once the weather has warmed a little. (I dont mind working in the cold but my backup car is a TR6 and I dont want it to dissolve before my eyes!).
Regards
James
-
Alan Chatterton
- Senior Member
- Posts: 2945
- Joined: Fri Feb 06, 2004 11:18 pm
- Location: Redditch, Worcestershire
Re: compression test
If it pinks in 3rd/4th when warm then the ignition is still too far advanced........... and a result of this is running on.
Set the timing to total TDC and see if that cures the running on problem (I think it will!)
By the way, does your car have a vacuum advance on the dizzy, if so , you are setting the timing with this disconnected..........?
Just a thought!
Set the timing to total TDC and see if that cures the running on problem (I think it will!)
By the way, does your car have a vacuum advance on the dizzy, if so , you are setting the timing with this disconnected..........?
Just a thought!
Alan Chatterton
Location; Redditch
DEL 33 1972 Lines Stag Estate Tartan Red
Blog http://vml3m.blogspot.com/
Location; Redditch
DEL 33 1972 Lines Stag Estate Tartan Red
Blog http://vml3m.blogspot.com/
Re: compression test
Alan,
Thanks for the reply! I'll try retarding the ignition. Last weekend I removed the distributor just to make sure everything was working as it should. The springs weren't broken and the weights were free to move. It all seemed OK to me. And yes - vacuum pipe was disconnected.
Regards
James
Thanks for the reply! I'll try retarding the ignition. Last weekend I removed the distributor just to make sure everything was working as it should. The springs weren't broken and the weights were free to move. It all seemed OK to me. And yes - vacuum pipe was disconnected.
Regards
James