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Cylinder bore wear question
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ukdave2002



Joined: 23 Nov 2007
Posts: 3503
Location: South Cheshire

PostPosted: Thu Sep 04, 2008 8:19 am    Post subject: Cylinder bore wear question Reply with quote

A few weeks ago I did a compression test on the Morris 8, with the engine warmed up the cylinders were all around 110psi, with a drop of oil this rose to 130, there was also blue smoke in the exhaust at anything but idle, so had concluded that it was re-bore time.

Just out of interest I did a leak down test yesterday and the lowest cylinder reading I got was 88%? Given the compression readings this seems very high?

Any veiws?

Dave
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Uncle Joe
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PostPosted: Thu Sep 04, 2008 1:12 pm    Post subject: Reply with quote

UK, you have intriqued me here. Exactly how did you perform the test?
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ukdave2002



Joined: 23 Nov 2007
Posts: 3503
Location: South Cheshire

PostPosted: Thu Sep 04, 2008 2:32 pm    Post subject: Reply with quote

A leakage test involves blowing compressed air in to a cylinder via the spark plug hole, when the cylinder is on its compression stroke, i.e. all valves are closed.
Before you open the air into the cylinder you adjust an airflow meter to 100% (or 0% depending which way round the meter reads) this takea acount of any air leaking in the hoses and connecters etc, then you let the compressed air into the cylinder and get a reading of the % lost. If it is significant you then trace the loss, you may feel air coming out of the exhausts or carb, which would indicate a leaky valve, bubbling in the radiator would suggest a blown head gasket etc.

The guide is that anything above 80% ie 20% leakage is ok on an older engine, high performance engines should leak less than 5%.

By the way the 88% I refer to means 12% leak not 88% Shocked




The leakage tester I have is built into my Crypton Analyser (yet another reason to fork out 30 and buy one!! Very Happy Very Happy ) you can see the inlet and outlet pipes hanging off the handle of the side of the unit. Its the meter on the lower rhs of the unit.

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Uncle Joe
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PostPosted: Thu Sep 04, 2008 3:26 pm    Post subject: Reply with quote

It was the 88% that got me confused...did you listen for any leakage? there are three main places to do that, as I'm sure that you are aware...

The one thing that puzzles me about the engine is that the compression values seem to high. It is a sidevalve isnt it?
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ukdave2002



Joined: 23 Nov 2007
Posts: 3503
Location: South Cheshire

PostPosted: Thu Sep 04, 2008 3:44 pm    Post subject: Reply with quote

HI UJ, yep its a side valve, compresion ratio is 6.5:1.
I thought 110 PSI was on the low side, am I wrong?
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Uncle Joe
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PostPosted: Thu Sep 04, 2008 3:55 pm    Post subject: Reply with quote

I would have expected around 90-100 psi, measured with a warm engine and fully open throttle. I dont ever remember a standard side valve being as high as yours, unless it had a skimmed head or block...
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ukdave2002



Joined: 23 Nov 2007
Posts: 3503
Location: South Cheshire

PostPosted: Thu Sep 04, 2008 5:20 pm    Post subject: Reply with quote

I don't know the history of the engine so no idea if it has been modified, think I'll whip the head off at the week end and have a look. With what UJ advised re the compression and the fact the leak down test was good, may be its not in to bad shape? it does smoke a bit though, any tips on what I should look for?
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Rick
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PostPosted: Thu Sep 04, 2008 6:31 pm    Post subject: Reply with quote

probably a silly question but how old is the oil in the engine?? if its old stuff gone off, might be worth putting something half decent in, as old could have been diluted with condensation, fuel from a leaky pump or whatever

R
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Various 1920s-1960s - Austin, Morris, Commer, Dodge etc.
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Uncle Joe
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PostPosted: Thu Sep 04, 2008 6:44 pm    Post subject: Reply with quote

If the bores are OK, then the only other place is leakage through the valve guides really.

Oil quality can make a difference, of course. There is one thing that I always do though with sidevalves. I think other oldies on here do the same. Mix a little Castrol R40 in the petrol. It works as a UCL, and makes starting a little easier for some reason.

I know its on a different scale, but I do this with my lawn mower, and I guarantee it will start first pull after the winter lay off. it smells better, and the neighbours simply cannot understand why it runs noticably better than theirs!
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Rick
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PostPosted: Thu Sep 04, 2008 6:48 pm    Post subject: Reply with quote

I've got my 6v battery on charge at the mo, if I get chance I'll fire up the Z van as that has a healthy engine in it, and once warmed through I'll do some comp tests on that, for comparison purposes

RJ
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Rick (OCC Admin)
Various 1920s-1960s - Austin, Morris, Commer, Dodge etc.
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ukdave2002



Joined: 23 Nov 2007
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PostPosted: Thu Sep 04, 2008 10:26 pm    Post subject: Reply with quote

Thanks Rick that would be a really useful comparison.
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buzzy bee



Joined: 23 Nov 2007
Posts: 3397
Location: South Cheshire

PostPosted: Thu Sep 04, 2008 10:40 pm    Post subject: Reply with quote

Hi

Have you used a cheap oil in it, with detergent in it?

If you have then you may have cleaned it all out, I did that with mine, and it has stopped smoking a little, still smokes alot, but not as much, due to carbon buildup and the like.

Also what are your rings like, gummed up? It may be that your oil ring is gummed??

Cheers

Dave
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Rick
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PostPosted: Sun Sep 07, 2008 10:11 pm    Post subject: Reply with quote

ukd, I popped a note of my compressions on the Z van thread

http://www.oldclassiccar.co.uk/forum/phpbb/phpBB2/viewtopic.php?t=4484&start=15

they were a bit all over the place, but might improve once the engine has run more frequently and the rings given chance to fully free up Smile

Rick
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Various 1920s-1960s - Austin, Morris, Commer, Dodge etc.
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ukdave2002



Joined: 23 Nov 2007
Posts: 3503
Location: South Cheshire

PostPosted: Mon Sep 08, 2008 7:51 am    Post subject: Reply with quote

Thanks for the info Rick; hopefully you have a couple of stuck rings that will free up on the middle cylinders with a bit of use.

I took the head off the 8 yesterday and measured the bores, the unworn lip at the top of the cylinder was 2.303" and the bores were all worn by between +0.006" & 0.008"at their most oval points.
From what I can Google this amount of wear is just beyond what is an acceptable tolerance? Any views
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Uncle Joe
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PostPosted: Mon Sep 08, 2008 12:13 pm    Post subject: Reply with quote

I'm not really sure that I should pass any opinions on this, but here they are anyway.

My experience of side valves is that they tend to like oil anyway. So as long as it is just a light haze, I wouldnt worry. Having said that though, my thumb rule is that if a lip can be felt at the top of the cylinder, rebore them. If the smoke is just a puff when changing gear, then its just a case of re-ringing.

Commenting here on Ricks values, if that had been my engine, and the fault didnt disappear with a little running, then I would do a strip NOW, because the beginnings of a ''not-to-serious-but-could-be-soon'' crank problem is there. only the older ones on here will know the reasoning behind that statement....
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