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Discussion Starter #1
I want to run a compression te

I want to run a compression test on my 365BB this weekend just to see what the figures are - and yes I know a leakdown testwould be more revealing but that can come a little later.

So my question is this - is my procedure correct?

I will get the temps up to normal first, then I intend to remove all 12 plugs and then, with the throttle wide open, I will run the test on #1, #2, #3 etc. Then I will squirt a little oil down the plug hole of each cylinder in turn and re-run the test.

I have been told I should leave the other 11 plugs in place (and disconnect the HT leads, of course) rather than remove them all.

I can't see what the difference will, be except for the load on the starter when turning the engine over on the key, but I may be missing something.

What values should I be expecting to see? Wet / Dry? 160-170-190 ? I will, of course, post these when I have the results whether good or bad.

Any suggestions or comments welcome.
 
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Discussion Starter #2
Hi Simon,

Unfortunately a d


Hi Simon,

Unfortunately a debate rages "in some circles" on correct procedure.

I'm not one that needs debate. The correcrt procedure is with all plugs out, full throttle, crank until needle no longer climbs, record, proceed to next cylinder.

After running thru the first pass, recheck any cylinders that warrant a double check. If all cylinders are within 15 lbs of each other and above 150-155-160 lbs there would really be no need for the oil test imo.

Reason is, after a certian amount of pressure is reached, each ensuing crank pushing against the retained pessurebegins to act on the rings causing them to expand and seal to their full ability.

HTH's
 
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Discussion Starter #3
Here's one I have heard. D

Here's one I have heard. Disconnect the Dinoplex fron the wiring harness prior to cranking with the plug wires off the plugs. Heard that you could "blow" the unit if not. Don't know if that's true, but considering the replacement cost it might be a safe precaution.
 
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Discussion Starter #4
Thanks for that Bill. I have o

Thanks for that Bill. I have only just read your message and I can tell you that I did NOT disconnect the Dinoplex but I did remove the HT lead from the coil. My unit suffred no problems at all, thank goodness.

Details of the compression test follow.
 
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Discussion Starter #5
Here are the results.

First


Here are the results.

Firstly I should say that the reason I decided to run a compression test was that my car started to smoke out of the passenger of the exhaust for a few minutes whilst on a run recently. Not a little but quite a lot. Someone following said that they thought I had blown the engine. Then it stopped just as quickly as it had started. I had recently changed the oil and the level was above the max mark when hot so I drained out 2.5 litres and the level is now about 1/3 between the min and max marks when hot. Then last weekend I was driving the car and noticed the same thing happen again. For about 30 seconds, and before the car was fully warmed up, there was a lot of smoke visible in the rear view mirror. It went away as suddenly as it appeared. This is definitely oil smoke.


On Saturday I ran the car up to operating temperatures - and had the same smoking occur briefly when cold - and then took out all the plugs, disconnected the coil HT lead and ran a compression test with the throttle wide open when I was cranking the car over. The next morning I ran the test again with the engine absolutely cold to see if anything changed. The results where:

Cyl.......Hot......Cold

#1.......162.......159
#2.......162.......157
#3.......158.......156
#4.......161.......154
#5.......159.......158
#6.......159.......159
#7.......157.......154
#8.......158.......157
#9.......161.......155
#10......160......158
#11......158......158
#12......158......158

These seem fine to me, in fact I am very pleased with them. I realise the 'Cold' test does not really represent anything but the figures seem close enough to me to indicate that there are no major problems here.

All the plugs are clean and not oily. I checked the timing with a strobe light and found it to be out. It was set to PM1-6 which is TDC I believe. I adjusted it to AF-18 at 900 rpm and checked it was at A5-38 at 5,000rpm, which it was. Car runs a lot smoother and seemed about 5-10% more powerful on a test drive. Carb balance is roughly correct - not perfect but showing between 3 and 5 on my gauge which ranges from 1-10 - and I'll set these up accurately next weekend. The car still smoked when started up from cold BUT on the other bank this time!! It went away again in around 30 seconds.

What really confuses me now is what is causing this random smoking when cold.

Could this be the CEC (Crankcase Emmission Control) system being blocked or somehow be forcing oil into one of the small tubes going into the car

For the record the car has covered 18,560 miles with all records, it was nice sunny day both days, around 25C and I am in London so I am around sea level.
 
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Discussion Starter #6
Simon,

Compression looks ni


Simon,

Compression looks nice. Thanks for the follow-up.

Assuming the car hasn't been abused 18K miles is nothing on BB engines. The sporadic nature of the annomaly has me somewhat puzzeled. From your description it seems most likely something in one of the top end systems is building up a pool of oil then dumping into the intake somewhere/somehow.

It's been too many years since I did 365BB's with enough frequency to remember exactly how the crankcase vent system works, but doesn't all the blowby go directly into the air cleaner housings? Is there a crankcase vent to atmosphere that may be plugged?
 
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Discussion Starter #7
The blowby gets 'injected&

The blowby gets 'injected' into the inlet manifolds. I had teh same thought as you about something causing oil to be collected and then dumped into the CEC. Can't see what though.

Attached is the diagram from the owners manual. The workshop manual has the same picture and says that the CEC system needs to be cleaned with the 'correct cleaning fluid' (???) every 20k miles but doesn't say what that fluid is or how to do it.

 
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Discussion Starter #8
Simon,

To clean things like


Simon,

To clean things like the CCV system I use Brake Clean or Carb Spray in the aerosol cans. But you could use Acetone or something simular that will melt carbon build-ups.

Two things came to mind seeing this old system. We added a piece of course steel wool as a vapor/mist seperator ala later cars, and as I recall if some of the jetted intake vents become plugged the oil backs up and eventually gets sucked into any open port in larger quantities than if a little goes into 12 ports.

Might not be a bad idea to clean everything and add the steel wool to see if that helps.
 
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Discussion Starter #9
I have a compression check que

I have a compression check question. In regards to my PPI thread earlier, would a leaking head gasket cause a bad compression check?

The shop that had worked on it previously mentioned that it had poor compression on the rear bank (77 308GTB) but the front was fine. Also, it had an oil leak that was dripping oil onto the belts.
 
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Discussion Starter #10
Sean,

The short answer is i


Sean,

The short answer is it's doubtful a head gasket would show up checking compression.

That said:

You can see from the numbers above, taken in accordance with strict guidelines to ensure accuracy (I have complete faith in Simons ability to conduct quality operations) how a normal compression test looks on a good engine. That same engine tested by someone less methodical could have gotten numbers that were all over the map. Every test is subject to the personell conducting it. Quality personell achieve quality test results (good or bad), less than quality personell conducting the same tests often (not always, some people live on luck) achieve innaccurate and thus worthless test results.
 
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Discussion Starter #11
Thanks for the confidence you

Thanks for the confidence you have in my ability, JRV :)))

I guess you stuffed the steel wool in the rubber pipe marked as '2' in the diagram above.

I'll try some carb cleaner on the CEC and see how it works. I'll report back when it is done.
 
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