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Compression Test

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Having just done a compression text I've got a reading of 60-70 on every cylinder, what should the PSI reading be in a healthy engine?

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LC turbo I'd guess 120ish although I don't think Lotus actually specify them.

HC NA I think good tends to be 140ish, HC Turbo would probably be below that and LC turbo lower still (due to lower compression ratios of turbo engines)

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Were those readings done at wide open throttle setting while cranking it over? I thought even the turbos with their lower CR were still in the mid 80's (but maybe I remember wrong).

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Book value for LC Turbo is 130psi. Taken with all the plugs out and throttle wide open....disconnect the ignition at the connector to the distributor and turn off the fuel pump by tripping the inertia switch....allow the engine to crank for about 10seconds for each reading.

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Having equal readings over all four cylinders is a good sign though :thumbup: Why are you performing the compression test do you have a problem or just giving it a general health check!

Regards danny

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I have a lot of oil over the manifold, but no obvious sign of where it's coming from, turbo oil drain pipe is fine, and I'm not sure oil would end up getting to the manifold from a leak in the head gasket. But I did wonder if it could be a rocket cover gasket leaking as a result of the head gasket going and leaking pressure in to the oil forcing it out at the rocket cover?! The reason I think I think it's the head is because this happened suddenly and now it's a pig to start and won't idle.

I tested one cylinder at a time with the other 3 plugs in, but I did not have the throttle wide open. Would this make much difference to having all plugs off and throttle open? Readings are constantly low from what I can see across all cylinders..

Oh, not sure I mentioned this, it's a LC Turbo. So consensus is that it should be 120 or 130 PSI, assuming my readings are accurate it suggest I do have a problem.

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Not having the other plugs out and not using full throttle completely negates your test results! Unless the throttles are open you'll get much lower figures...the engine can't inhale enough air to compress in the first place! Try again in the Approved Manner...I'd be very surprised if your oil leak has anything to do with compression... the cam towers and covers are a noted spot for oil leaks....dribbles onto the exhaust and into the plug wells.

As for the engine problems...the oil supply to the cams runs up through one small drilling in the head, not really close to the cylinder seals...so,to get compression pressure in to the oil system would be difficult. You can get compression pressure back up the valve guides, but not likely to give the effect you relate. I assume your plugs aren't spherical lumps of oil grot?

Edited by molemot
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Redo the test correctly then post your readings. And yes, the cam towers/rocker covers and cam end caps can all leak like a sieve without warning.

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I'd best get out there and do it properly this time. Fingers crossed will be a simple rocker cover removal job then. There was some oil in one plug well.

Where's the best place to disconnect the fuel pump from?

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I don't think it has been stated here but you have to do the compression test on a hot engine. Purchased a tester myself but have been putting off the test as fairly certain the valve quides are letting oil into the engine hence oily plugs.

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Yes...sorry...forgot that. Engine needs to be at operating temperature. Fuel pump is switched off by pulling out the red bit on top of the inertia switch, which - on mine - is on the RH wheel arch in front of where the battery is. It's a squarish black box with an electrical plug at the bottom and the red telltale (which sticks up when it's tripped) coming out the top. You can pull the telltale out and that switches off the fuel pump.....the ignition is switched off by unplugging the 3 wire connector going from the distributor to the ignition box.

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I've been advised to engage the clutch when carrying out a CT - it'll take the strain off the starter and battery as you effectively won't be turning over the gearbox too.

It'll also make the cranking speed faster to boost your readings!

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Also rememer that the cheap compression gauges are crap! Mine gave a compression on my 924 N/A of near 200 psi.

All 4 the same (Regardless of throttle adn other plugs) is a very good sign.

Repeat the test with all the plugs out and the throttle open and see if it's the same.

If it's still low then chuck a bit of oil in each bore adn try again - if it improves *significantly* (It'l improve a litte bit) it's probably rings or liners worn.

My money is on a cam tower leak though... TADTS...

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I have a 1988 Esprit turbo, engine running smooth, no oil on plugs, running clean, great power, I did a compression test today out of interest and found three cylinders at 75 and on at 90, fuel pump off, throttle wide open, any thoughts? 

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