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Low Compression on #1 cyl.  Rate Topic 
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 Posted: 02-03-2017 01:01 am
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Paul Koehler
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Ran a compression check and discovered the following:
cylinders 2,3,&4 were in the 120 range and cylinder #1
came in at 35.
Could all you smart folks suggest a flow chart type series of steps that should be undertaken in order to find the root cause and correction needed to solve the problem?

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 Posted: 02-03-2017 04:27 pm
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dwalls1
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Guess I'd start with valve clearance, but to have just #1 with tight clearance might be unusual. Maybe first would be another comp check with oil added to cylinder. Might help determine if it's valves or rings but, again on just one cylinder might be unusual. There are lots a guys here that will have a better answer. Good Luck.

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 Posted: 02-03-2017 11:32 pm
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jomac
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What did the spark plug look like as compared to the others,

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 Posted: 02-04-2017 01:01 am
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Esprit2
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Repeat the compression test on the low cylinder just to make certain it wasn't simply a procedure screw-up on your part. Specifically, make certain the throttle is held wide open during the test. The battery must be fully charged, and capable of spinning the engine over at 200 rpm or better. If not, use jumper cables to a running vehicle.

JH specifies 110-130 psi for a cold engine. Lotus specifies 150-170 psi for an engine that has first been run long enough to bring it up to full operating temperature before doing the test. In either case, pressures for all four cylinders should be within 10 psi. 30 psi is clearly a bit low... like hole-in-the-piston low.

If the pressure re-tests low, then squirt some oil into that cylinder. It's difficult to get even distribution of the oil around a piston in a slant cylinder. So, with the piston at the bottom of it's stroke, aim for the cylinder wall above the high side of the piston. Give it a few squirts, then before the oil all runs down hill, turn the crank through a couple of revolutions, scraping oil into the piston-cylinder gap, and around the piston. Then repeat the compression test for that cylinder. 200+ rpm with the throttle held wide open.

If the new reading is dramatically improved, then the rings were not previously sealing in that cylinder and the oil helped fill the gaps, improving the result. Oil is not a fix, so it's time for a ring job.

With oil added, if the pressure result is pretty much unchanged and still low, then the rings are probably not the problem. In that case, it's most likely a burned or otherwise leaking valve... or several. It could also be a burned piston, collapsed ring lands, or a burned-through crown.

In any case, a persistent 30 psi compression reading is not going to fix itself with medicine poured in, or with anything you can fish into the hole. Having some idea what's wrong before you start is nice, but the fix will involve some degree of engine disassembly. At least removing the cylinder head, and perhaps a complete tear down.

Good Luck,
Tim Engel

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 Posted: 02-04-2017 03:07 pm
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Paul Koehler
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Thanks for the advice. I did the comp. check three times and then the oil to the cylinder procedure with no appreciable improvement.It is a 100,000 plus mileage engine that has had regular attention (oil&filter;plugs; timing belt/bearings; waterpump),but never been opened up. Due to location, it only gets driven 6 months a year and then usually less than 3000 miles.
I think I'll start by switching heads from my spare parts car, so that hopefully I'll have a driver for spring, and then see what attention the original head needs.

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 Posted: 02-05-2017 02:14 am
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Bfitz241
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do you have an air compressor? If you do, adapt the air compressor to the compression tester hose.
Bring #1 to TDC. Trans in gear E brake on. Pressurize the cylinder.
Listen at the carb, if you hear air bad intake valve, listen to the exhaust, if you hear air, bad exhaust valve. Listen at the oil filler cap, if you hear air, holed piston.
you can google "leak down test" for more detail.

Sorry, just saw you've got a spare head....taking the old one off will provide a definitive answer...hope it's something simple.  Good luck

Last edited on 02-05-2017 02:34 am by Bfitz241

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