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Compression Test Results

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kindofblue

kindofblue

Jedi Warrior
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First compression in 14 years. Can you believe it turns right over. (once I disconnected the fuel pump so it wouldn't make that annoying buzzing sound.)

1- 140
2 - 105
3- 105
4 -95
5- 45
6- 110

All of them got about 50 on the first puff. I put some all in the hole for cylinder #5 and the compression didn't come up. I pulled the rocker cover off and the rockers and springs are moving. Could a valve adjustment bring these up?
 
That's a very low compression number on #5.
If it didn't come up with a shot of oil in the cylinder then it's valves or head gasket.
#4 is lowish also which could indicate head gasket.
I think the valves would have to be hanging open or leaking a lot to be that low, you should be giving it about 8 compression strokes per cylinder to get a decent reading.
I'd certainly turn the engine to get the cylinder on the bad cylinder on the compression stroke and check the valve clearance before you start pulling off the head.
 
I have similar results on the TR3 -- one low cylinder. It actually runs quite well in spite of that. I expect to pull the head and find the #3 exhaust valve at fault but before I do I will undo the manifold nuts, pull the manifold back from the head and pump air into #3 plug hole with the valves closed (tranny in gear, brake on). I expect to be able to feel air coming out the #3 exhaust port. Will still be pulling the head but thought I would experiment a bit first.
 
Did you do the test with WOT ?
 
WOT plus I have a little thingy I made out of 2 square pieces of cardboard wrapped in and connected by a length of duct tape. One of these in the throat of each SU holds the piston up out of the way w/o restricting air flow (and w/o getting sucked into the manifold).
 
kindofblue, I think you have a couple of burnt valves, but you didn't say if you got any backfire's through the carbs, so my guess is an exhaust valve. Spring is near, so hurry. Wayne
 
Remember this car hasn't run in 14 years. Today was the first time the starter has turned the engine over in that much time. It isn't backfiring because I don't have any fuel to the carbs. I disconnected the fuel pump because it was making quite a racket.

I was running compression to see the internal condition of the engine. Fortunately, it doesn't look like bottom end problems. I am wondering if the valves may be out of adjustment from sitting so long. Could adjusting the valves help bring that up?
 
As long as it's making some compression you have a half a chance. The real proof would be to do a leak down test. If you determine how fast its leaking out that will give you a good clue on where its going. Adjusting the valves is a long shot but it's cheap and quick. Besides head gasket add bad rings into the list of possibilities. I had an engine once that developed a small hole in a piston and made "some" compression but skipped like the devil when being driven (not to mention quickly fouling the spark plug in that cylinder). Recently changed the head on my MG since one of the valves had receeded so far into the seat that it was held partially open all the time. My first actual experience with dreaded soft seat/no lead gas fiasco. Bob
 
It's a little hard to tell with an engine that's been sitting this long. The first question & unknown answer is, was the compression low when it last ran. It's unusual to have one cylinder so much lower than the others.

First, check to make sure that you don't have a zero lash adjustment on any of the valves.

Real possibilities are that one of the valves is sticking in it's guide. If a valve IS slightly sticking open, it would show a greater valve lash (clearance) than normal. Apply some penetrating oil to the valve guide tops & crank it over for a bit. Then recheck clearances & compression.

Another common problem is that a small bit of carbon is trapped between a valve & it's seat. Again, this might show up as a slightly larger than normal valve lash setting. If this is the case, tapping on the valve/rocker end with a lead hammer will often smash or dislodge the carbon. Tap hard enough to force the valve open against it's spring. This will also free up a sticking guide. I know this sounds strange, but, I have had several engines come up to normal on a compression test by doing this. Keep track of any lash setting changes that may happen during the "fixes".

Last of all, try actually starting the engine & see how it runs & if it improves after running for a bit.

If these simple, but easy to try, remedies don't help, you will probably have to pull the head.
D
 
Course seeing it hasn't run in 14 years maybe the valve shafts/guides are all gunked up and holding them off the seats.
If you can get it started even briefly and retest the readings might come up a bunch.
As the guys say you should check with WOT (Wide open throttle) it makes quite a difference.
And yes adjusting the valve clearance could make a heck of a difference if they're set too tight and holding open, worth a check.
 
Fire it up and let it get to temperature a few times, adjust the valves, then test it again. Everyone so far has had good information. Gunk, carbon, burned valve, stuck ring, head gasket, zero lash, could be anything. My car sat for a long time also, even though I've put a few thousand miles on, it still runs better every time it's driven. Get it running then start hunting.
 
You must also considor the posability that after 14 years, a piston ring or two might be seized to the piston & not moving freely. This should work itself loose after the engine runs & warms .
 
Would a stuck ring cause this? I wonder if oil in the cylinder would fill the gap & raise the compression; probably so?

Couldn't hurt to spray some WD40 in all the cylinders before you turn it over too many more times, at least it would reduce the scraping of the cylinder walls if any rust formed in the bore/rings.

I would have done this 1st thing.

I'm going to look at a 20 tr rebuild that hasn't been run & first thing I"ll do is pray the cylinders before I try & turn it over.
 
[ QUOTE ]
...first thing I"ll do is pray the cylinders before I try & turn it over.

[/ QUOTE ]

Yes, oil and a prayer are both good things before attempting an initial start-up.
 
I poured oil in all of the cylinders a year and a half before hand cranking the engine. I also poured some oil in cyl to see if the compression came up and it did not.I was thinking some deposit or sticking valve could be the cause.

I will get some help from the local club next to start it and see if it clears it up at all. I am pleased and impressed with how willing the engine and starter was to turn over after all these years.

It wants to run real bad....
 
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