Triumph Repair: 1500 valve seals., crankcase pressure, valve seals

Question
QUESTION: Hi Howard,

I've spoken to you before about my 75 Midget with a 78 1500 engine, I rebuilt myself.

For the longest time, I thought I installed the rings incorrectly because I keep getting excessive crankcase pressure (oil blowing out the dipstick). Compression seems good so I started to think of other possibilities. I now believe this is a valve guide issue.

I base this on the following;

- good compression
- new Weber carb with Pierce manifold kit.
- Exhaust header installed, but I did NOT upgrade the factory exhaust (part of problem?)
- Cam was reground to "performance" when engine rebuilt.
- I did not check the valve guides when I rebuilt.
- Have oil build-up on spark plugs 3 and 4 cylinders, (minimal on 1 and 2 cylinders.)
- Thick wet looking oil residue on top side of all intake valves.

Do I need new valve guides?

Do you think installing valve seals will solve my problem?

I'm pretty sure I should install a new exhaust system too, what do you think?

Colin

ANSWER: Hi Colin,
Triumphs don't have valve seals plus even if you had worn guides it would not cause as much trouble as you have.

You said you have good compression but you didn't tell me what the readings were and what the wet test was. The dry test first then do a wet test. The wet test should not be any more than 10% to 15% higher than the dry test. It is the difference between the two tests that tells if it is a ring problem not the dry compression test.

An engine could have 135 PSI on a dry test and not smoke nor build crankcase pressure.
A second engine could have 140 PSI on a dry test and smoke and blow out all the seals and the dipstick.
Then do a wet test on each and see the first one with 135 PSI had a wet test of 138 PSI but the second one with 140 PSI dry would get a 180 PSI on a wet test and has failed and will have bad rings.

When you reinspected your rings, did you note if the second ring down was possibly up side down? Most second ring down are oil scraper rings and must not be installed up side down. Most top rings are not scraper rings but I have run across a few that were.

Run a dry test again (engine hot) and right after put about a spoon full (about 4 or 5 squirts from a squirt gun) of engine oil in the plug hole and run a second test right away. This Wet test tells the tail.
Tell me what the readings are. If they are less than 15% higher than the dry test I would bet some compression rings are up side down.

Valve stem clearance can not build crank case pressure because on the intake stroke it has a vacuum on it not pressure and when it is closed it only has outside air available to it. It never has combustion pressure on it. The exhaust guide has exhaust gas pressure applied only when the valve is open and that pressure never exceeds 1 and a half PSI and only just as the valve opens for as it is closing there is a vacuum applied to it, so not even an exhaust valve can cause crank case pressure. Bad guides cane burn oil but that is on the intake stroke when vacuum is applied to the bad guide which pulls excess oil from the crank case so if anything it would cause the dipstick to be forced inward not out.

My guess that you installed some compression rings up side down or you have a stopped up crank case vent system. I found that most engines are not critical on ring end gap as I have pulled down many engines that did not burn oil and they had a ring end gap of a quarter inch.
Let me know,
Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks for the reply.

I did the dry/wet test as suggested and the results are as follows:

Dry
148
152
158
165

Wet
170
191
180
196

I thought I might have put too much oil in cylinders 2 and 4 so a ran all four again, without adding more oil, and got the following

176
170
170
182

Does it matter much how much or how little oil you add for the wet test? (I can't seem to find a good oiler, the one I have is junk)

Thanks,
Colin

ANSWER: Generally a teaspoon is enough or 4 or 5 squirts from a hand pump squirt gun.
The oil floods the rings from above and seals the rings so they can't loose all the compression into the crankcase. When the Wet test shows more than 10% to 15% higher than the dry test it is an indication that a lot of compression is lost into the crankcase and that builds a high amount of crankcase pressure. The high case pressure then tries to blow out of the case vents, like the valve cover vent and that is usually orifice so it can't relieve all the pressure so the pressure builds and it will then push the dip stick up and force oil out of the seals and gaskets. When you have more than a 15% difference you should either purchase a leak-down compression tester or find a shop that has one and let them test the compression with a leak-down tester. If the results of the leak-down tester confirms the ring problem then you are safe in condemning a set of rings. That does not mean you should not be sure the case vents are ok because you can have both problems very easily.
Howard

---------- FOLLOW-UP ----------

QUESTION: So I take it my second readings were lower because the oil had a chance to drain down and therefore do not count?

I don't think my vent is the problem as it seems clear, (assuming you mean the one at ther valve cover).

Answer
Colin, crankcase pressure ONLY comes from ONE source. Your tests indicate a ring problem, so get a leak-down test and if that is "rings" also the only way you will stop blowing the dipstick out is to correct the ring problem. Since you say the vent system is OK.
Howard