What's the correct compression for Healey's?

[Johnny]

Getting ready to take compression readings on my BJ7 and in the shop manual General Data (page 10) they list "B.M.E.P. pressure as 142 psi at 2700 rpm. What does that mean?

Under cranking pressure they list 175 psi, I'm going to assume that is what I'm hoping to find. Assuming a minimal amount of wear what do you think would be an acceptable reading? There seems to be a lot of 'blow-by' coming from the engine.

 

[Randy Forbes]

Compression tests are full of variables, so some interpretation is necessary.

I've seen strong running engines, with little to no oil use, show cranking tests as low as 130Lbs (across all cylinders).

If you get 150Lbs, thatwould still be very good.

What you don't want to see, is a variance of pressures between cylinders; they should all be fairly close, within 15-20psi.

These tests should be done with the engine stinking hot, and prop the butterflies and dashpot pistons open while cranking. Crank each cylinder the same number of pulses (I use 6 on a 6-cyl, 4 on a 4-cyl...). Remove all six (6) sparkplugs before cranking tests. Valves should already be set to spec.

The best, in my opinion, static test of engine condition, is a leak-down test. Same prerequisite of stinking hot engine.

 

[tahoe healey]

I believe the quoted pressures are at sea level. I have found no difference with the butterflies open but that is by the book and takes a second to do. Up here (6500 ft)I'm very happy with 135 (+or- 2 psi) across all the cylinders. Someone told me it is 10 psi per 1000 ft. I think that is high. Harbor Freight sells a leak down kit. I've never done one but have read it tell more about any problems than compression tests.

 

[Johnny]

Okay, I've completed the tests. As Randy, and the shop manual, state; I took the test after running the engine for about 30 minutes and it was 'stinking hot'. Removed all plugs, blocked carbs open, pulled 'white' fuse (stops fuel pump). The top numbers are dry, the bottom are with a shot of oil in the cylinders, here are the results:

 

[Randy Forbes]

Looks like you're in good shape; nice consistant readings are always a positive sign!

 

[Johnny]

Thanks Randy, now for the 'REAL TRUTH', I've always had real bad fouling of the plugs on cylinders 4-6. About 2 months ago I removed the hose to the carbs from the valve cover and stuck it down between the motor and the firewall to see if that would help. I also cleaned up the plugs and put them back in the car. I've driven about 200 miles since then and have noticed the plugs have remained pretty clean. So now I suspect excessive blow-by was fouling the plugs. usually that situation is due to bad oil rings, correct? I mean since the compression seems to be acceptable what else could it be?

 

[Legal Bill]

Valve guides, poorly adjusted rear carb.

 

[Randy Forbes]

Valve guides, poorly adjusted rear carb.

I concur.

Depending on rockershaft wear, the top end could be "flooding" and then when you shut it down, the oil on top of the hardware can drain into the cylinders. Healeys have next to nothing in the way of valve stem seals.

The hose dangling between the carbs; is it dripping with oil?

 

[Patrick67BJ8]

Valve guides, poorly adjusted rear carb.

I concur.

Depending on rockershaft wear, the top end could be "flooding" and then when you shut it down, the oil on top of the hardware can drain into the cylinders. Healeys have next to nothing in the way of valve stem seals.

The hose dangling between the carbs; is it dripping with oil?

I purchased some valve stem oil seal caps to correct the oil dripping down into the cylinders but I can't seem to remember who I purchased them from(killed that brain cell).
I'll research to see if I can find the source.
Patrick

 

[Randy Forbes]

Valve guides, poorly adjusted rear carb.

I concur.

Depending on rockershaft wear, the top end could be "flooding" and then when you shut it down, the oil on top of the hardware can drain into the cylinders. Healeys have next to nothing in the way of valve stem seals.

The hose dangling between the carbs; is it dripping with oil?

I purchased some valve stem oil seal caps to correct the oil dripping down into the cylinders but I can't seem to remember who I purchased them from(killed that brain cell).
I'll research to see if I can find the source.
Patrick

Yes, it's not too difficult to find "umbrella-type" stem seals that will fit over the ends of the guides, and under the springs.

Anyone that's taking in heads to do valve jobs can probably set you up pretty easily.

 

[Johnny]

Valve guides, poorly adjusted rear carb.

I concur.

Depending on rockershaft wear, the top end could be "flooding" and then when you shut it down, the oil on top of the hardware can drain into the cylinders. Healeys have next to nothing in the way of valve stem seals.

The hose dangling between the carbs; is it dripping with oil?

No not really dripping. I don't think it's valve guides due to the plugs look really good now. (see photo above). Before the plugs were really black. Now that I'm saying that I noticed plugs 1 & 2 do look kinda black. Before plugs 4-6 looked even worse, so it could be valve guides on #1 & #2 cylinders.

BTW does it do any harm to leave the hose not connected to the carb?

 

[Bob_Spidell]

BTW does it do any harm to leave the hose not connected to the carb?

Nope (except for the mess it might make). Most older cars--including Healey 100s--vented the crankcase out a tube pointing toward the ground (aka 'road draft').

The one thing you don't want to do is block crankcase venting.

 

[BoyRacer]

Your rocker-arm bushings are worn out. Oil is shooting out everywhere. It is shooting out and up and into the "T" at the back of your valve cover, and then blowing out into the hose and going down into your rear carb air cleaner - and then getting sucked into your engine, and then oil-fouling plugs 4, 5 and 6.
Here's how to check it out. Remove your valve cover nuts and break loose the valve cover gasket - start your engine - let it idle - then lift off your valve cover. In a tight engine, oil will be dribbling off of your rockers. On the other hand, if the bushings are worn, oil will be shooting up like a gieser.
Or, you could just pull the rear air cleaner and check to see if it is filled with oil.

 

[Randy Forbes]

Your rocker-arm bushings are worn out. Oil is shooting out everywhere. It is shooting out and up and into the "T" at the back of your valve cover, and then blowing out into the hose and going down into your rear carb air cleaner - and then getting sucked into your engine, and then oil-fouling plugs 4, 5 and 6.
Here's how to check it out. Remove your valve cover nuts and break loose the valve cover gasket - start your engine - let it idle - then lift off your valve cover. In a tight engine, oil will be dribbling off of your rockers. On the other hand, if the bushings are worn, oil will be shooting up like a gieser.
<span style="font-weight: bold">Or, you could just pull the rear air cleaner and check to see if it is filled with oil.</span>

Works for me...

 

[Johnny]

Thanks Randy and all, good advice from all. I'll check the air cleaner and remove the valve cover and check that also.

Again, many thanks, as always the BCF comes to the rescue.

 

[glemon]

I agree witb the diagnoses, just wanted to say those are very good compression readings right where they should be both in raw numbers,and varience from cylinder to cylinder and with and without oil, IMHO.

 

[John Turney]

You don't really need to remove the rocker cover. Just remove the oil filler cap. One can see enough there without spraying oil all over the place.

 

[Johnny]

You don't really need to remove the rocker cover. Just remove the oil filler cap. One can see enough there without spraying oil all over the place.

Good advice John, thanks, I'll do that.

 

[why]

I must have missed the post stating the problem such as miss at high rpm or down on power, or hard starting, or perhaps oil consumption. If all those are ok along with your great compression, the fouled rear plugs which is only malady so far described (no oil consumption, some mist blow into carbs normal as in why tube is there), just take 30 secs and turn rear carb mixture screw in 1/2 turn. Sure worth a try before all that other stuff.