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Lack of Compression
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Trevor



Joined: 04 Feb 2009
Posts: 8

PostPosted: Mon Feb 16, 2009 2:04 pm    Post subject: Lack of Compression Reply with quote

Hi
I have just had a comprssion test done on my 1934 Morris 10/6 saloon and it demonstrates that I have a problem. The best result was on cylinder no 1 with a reading of 140 - all the others are below that down to 100 .
Is there any simple cure for this problem or do I have to get a full rebore/rebuild?
Any advice would be gratefully received.
Thanks
Trevor
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Rick
Site Admin


Joined: 27 Apr 2005
Posts: 21005
Location: North-west UK

PostPosted: Mon Feb 16, 2009 2:09 pm    Post subject: Reply with quote

Hi Trevor

Is the engine showing any signs of wear otherwise, ie smoke from the exhaust, or reluctance to start? If not, I'd not be overly worried about compressions that were all into 3 figures, even if there is some variance.

R
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Rick (OCC Admin)
Various 1920s-1960s - Austin, Morris, Commer, Dodge etc.
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Trevor



Joined: 04 Feb 2009
Posts: 8

PostPosted: Mon Feb 16, 2009 2:48 pm    Post subject: Lack of Compression Reply with quote

Hi Rick
Yes, there is some blue smoke from the exhaust and a seeming lack of power.
It has been suggested to me that what it needs is a complete rebuild - rebore, new exhaust valve and seats etc. but all that is very pricey!
Trevor
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baconsdozen



Joined: 03 Dec 2007
Posts: 1116
Location: Under the car.

PostPosted: Mon Feb 16, 2009 3:24 pm    Post subject: Reply with quote

Try squirting a drop of oil into the cylinders and try agai,You want to try and wet the rings and bores,not the valves.If the readings rise,then it shows the bores or rings are bad.
If it doesnt its probably the valves at fault,much cheaper than a rebore,pistons and rings.
The readings aren't that horrendous for an older engine though,might be worth checking timing etc to make sure the power loss isn't something else.
The blue smoke might just be a blocked breather or too thin oil.
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peter scott



Joined: 18 Dec 2007
Posts: 6175
Location: Edinburgh

PostPosted: Tue Feb 17, 2009 9:08 am    Post subject: Reply with quote

Hi Trevor,

I would try grinding in the valves. It costs nothing and will give you a look at the bore wear at the same time.

Peter
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1939 SS Jaguar 2 litre saloon
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ukdave2002



Joined: 23 Nov 2007
Posts: 3490
Location: South Cheshire

PostPosted: Tue Feb 17, 2009 9:35 am    Post subject: Reply with quote

Hi

Before you strip anything down you should do a leak down test, it will tell you far more about the state of the engine than a compression test, it also highlights where about where the problem is.

This post may help; http://www.oldclassiccar.co.uk/forum/phpbb/phpBB2/viewtopic.php?t=5614

If you can't get hold of a tester, simply feeding compressed air into the cylinder can often identify the cause of the problem.

140 actually seems high for a Morris 10, blue smoke can down to worn big end bearings; the worn bearings will let more oil on the cylinder walls than the oil rings can deal with.

If the leak down test does not reveal anything, I'd whip the head off, measure the bores (where most oval) you can do this with a feeler gauge measuring the piston to cylinder clearance and at the same time take a look at the valves.


Dave
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roverdriver



Joined: 18 Oct 2008
Posts: 1157
Location: 100 miles from Melbourne, Victoria, Australia

PostPosted: Tue Feb 17, 2009 11:01 am    Post subject: Reply with quote

Alas KLG was probably the last spark plug manufacturer to make demountable plugs. A very handy tool is (if you can locate one of those plugs to suit your vehicle) unscrew the sleeve that holds the porelain in place. Discard porcelain. fit a tyre valve in its place and reassemble.

Screw your new air device into a spark plug hole. Turn the engine to compression TDC for that cylinder, then apply pressure through the tyre valve.

Slight hiss audible via oil filler is acceptable. more major hiss suggests rings worn. Hiss from exhaust pipe is probably burned exhaust valve
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baconsdozen



Joined: 03 Dec 2007
Posts: 1116
Location: Under the car.

PostPosted: Tue Feb 17, 2009 11:29 am    Post subject: Reply with quote

You can also buy a flexible tube that has an airling fitting on one end and the other has adaptors to screw into the plug hole.Try "valve holder" on ebid auctions .They are also used to hold the valves in place,by pressurising the cylinder head at TDC to allow oli seals to be replaced with the heads still in place.
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