Lotus Elan

Poor compression - cause? Updated

PostPost by: elancoupe » Fri Jul 10, 2020 8:29 pm

pharriso wrote:
Spyder fan wrote:Or you could use this stuff https://www.directcarparts.co.uk/worksh ... vxEALw_wcB

I was offered this by a Snake Oil salesman


Does it cure gout as well?


I would be first in line if it did..... :(
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PostPost by: 69S4 » Sat Jul 11, 2020 6:39 am

Spyder fan wrote:Phil,
Shame you can’t take a rebuilt engine home as hold baggage next time you visit the UK ( next year?). I have the Q420 spec engine sitting in its cradle doing nothing. Not for general sale, but open to negotiation to friends in need 8)



I have a friend who took a complete motorcycle from the U.K. to the US as hold baggage when he flew there frequently in the 80’s. Like Johnny Cash he took it a piece at a time :D The front forks attracted a bit of attention on X Ray and they opened his bag to have a look. “We do have some strange stuff come through” the officer said as he searched, “someone had an engine in their suitcase a few weeks ago”. “ Yes, that was me” my friend said...

I’m not sure you could do it now, it’s all become very serious.

Wasn’t there a similar fix your engine gloop around in the 60’s? I do remember buying it to try and fix my worn out scooter engine. Was it made by Holts or someone? Did nothing then and I don’t suppose anything’s changed.
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PostPost by: pharriso » Sun Jul 12, 2020 2:08 pm

2cams70 wrote:Another test you could consider is a "power balance" test. Basically this entails hooking up an accurate low RPM range tachometer to the engine and noting the idle speed. Once stabilized short each spark plug in turn (slide the boot up on the HT lead at the spark plug and short to ground with a long handled insulated screwdriver) and note the drop in speed when each cylinder is independently isolated. The one that has the least RPM drop will be the most problematic cylinder worthy of further investigation. Could be further good backup information for what the compression test reveals. Your compression readings are fairly even however. Usually for a worn engine some are worse than others.


This is a good test for identifying 1 or 2 bad cylinders, however in mny case the compressions are all pretty even, so it would not tell me anything.
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PostPost by: pharriso » Thu Jul 16, 2020 3:32 pm

Leakdown Tester arrived to (hopefully) get fuller analysis. Before testing leakdown repeated the compression test with the good (Lisle) tester (warm engine, dry):

Cyl 1 Cyl 2 Cyl 3 Cyl 4
167 178 178 172 psi

So not bad, not all sure what the compression ratio is on the engine since the head is an unknown.

Leakdown test results:
Cyl 1 Cyl 2 Cyl 3 Cyl 4
5% 2% 3% 3%

The leakdown test results are really good!

Back to why I am testing: What would cause a lot of crankcase pressure & oil being flung out the breather hole in the block to the tune of 1/4 pint every 20 miles or so.
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PostPost by: gjz30075 » Thu Jul 16, 2020 4:26 pm

following.....
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PostPost by: sprintsoft » Thu Jul 16, 2020 4:38 pm

that’s some impressive results you have there Phil!

Can you hear the air leakage on the oil filler cap or dipstick hole?

Are you getting any air (bubbles) in the coolant?

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PostPost by: Andy8421 » Thu Jul 16, 2020 4:39 pm

pharriso wrote:
Back to why I am testing: What would cause a lot of crankcase pressure & oil being flung out the breather hole in the block to the tune of 1/4 pint every 20 miles or so.


The breather hole is in the head?
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PostPost by: pharriso » Thu Jul 16, 2020 4:45 pm

sprintsoft wrote:that’s some impressive results you have there Phil!

Can you hear the air leakage on the oil filler cap or dipstick hole?

Are you getting any air (bubbles) in the coolant?

Iain


No to either...
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PostPost by: pharriso » Thu Jul 16, 2020 4:47 pm

Andy8421 wrote:
pharriso wrote:
Back to why I am testing: What would cause a lot of crankcase pressure & oil being flung out the breather hole in the block to the tune of 1/4 pint every 20 miles or so.


The breather hole is in the head?


No, this is with my very strange head without a breather box. There is no oil drain to the block & no breather hole to the airbox. There are several of these heads knocking about with shortened runners, was discussed by another poster in a seperate thread. Let me see if I can find it.

The only "breather" available is the hole above the fuel pump, used with a oil/air seperator on Ford Kent engines.
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PostPost by: sprintsoft » Thu Jul 16, 2020 4:54 pm

1/4 pint in 20 miles is pretty extreme even for the most worn engine, and your results are good.

given your breather setup have you got a baffled sump maybe where the oil cannot drain down fast enough?
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PostPost by: Donels » Thu Jul 16, 2020 5:51 pm

I don't think your pressure gauge is accurate as 178 psi equates, roughly, to a 12:1 compression ratio. If its blowing oil out and using oil at the rate you describe its time for an overhaul.

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PostPost by: sprintsoft » Thu Jul 16, 2020 6:45 pm

Dave, if I understand correctly it's not actually burning the oil lost, it's getting blown out of a defective oil/air separator. Iain
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PostPost by: promotor » Thu Jul 16, 2020 7:15 pm

Donels wrote:I don't think your pressure gauge is accurate as 178 psi equates, roughly, to a 12:1 compression ratio. If its blowing oil out and using oil at the rate you describe its time for an overhaul.

Dave


Maybe I've misunderstood but that sounds a bit off? Standard 9.5:1 Twincam with standard cams is rated @ 170 lb sq.in at cranking speed.
I had an engine (xflow) with 10:1 compression and a 272 duration cam and got 190 psi.

Compression test / check is not really a good test of engine health without other info relating to static compression ratio and cam duration, unless you are simply using the compression test to show balance (or lack of) across the cylinders and also have a known figure for a particular spec of engine.
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PostPost by: pharriso » Thu Jul 16, 2020 7:27 pm

promotor wrote:
Donels wrote:I don't think your pressure gauge is accurate as 178 psi equates, roughly, to a 12:1 compression ratio. If its blowing oil out and using oil at the rate you describe its time for an overhaul.

Dave


Maybe I've misunderstood but that sounds a bit off? Standard 9.5:1 Twincam with standard cams is rated @ 170 lb sq.in at cranking speed.
I had an engine (xflow) with 10:1 compression and a 272 duration cam and got 190 psi.


I understand the logic (12:1 x 1 bar (14.7) = 176 psi, but published figures say minimum compression for a normal twin cam is 160 psi & for a high compression engine minimum is 170 psi.

promotor wrote:
Compression test / check is not really a good test of engine health without other info relating to static compression ratio and cam duration, unless you are simply using the compression test to show balance (or lack of) across the cylinders and also have a known figure for a particular spec of engine.


Which is why I ran a leakdown test, the result 2-5% on all cylinder is very good.
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PostPost by: pharriso » Thu Jul 16, 2020 7:28 pm

sprintsoft wrote:Dave, if I understand correctly it's not actually burning the oil lost, it's getting blown out of a defective oil/air separator. Iain


Correct
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