Balance Pipe Repair

[AmilcarJohn]

Since I bought my Jupiter 6 months ago, I have been chasing an issue with plug oiling the two offside cylinders. Since the other bank was unaffected, I initially assumed rich mixture on the offside carb (Del'Ortos are fitted). After much adjustment, cleaning and checking, I eventually took the logical step of swapping the carbs left-to-right which had absolutely no effect on the problem. The plug oiling has now got worse and shows wet oil on the plugs and oil smoke in the exhaust. Looking down the inlet tract I can see oil in the balance pipe, so I assume the centre o-ring has failed.

The engine is reasonably recently rebuilt (not by me) and the car is in regular use, so I would rather avoid a full strip-down. The technical notes on this site suggest two repairs without stripping the crankcase -either 1) blocking the balance pipe and creating an external pipe between the carb stacks, or 2) cutting the pipe inside the pushrod covers and joining the two with a flexible pipe through holes cut in the covers. I am doubtful about effectively sealing the balance pipe without removing the cylinder head, since access is limited and the best way would presumably be to hammer home a tapered lead plug since the pipe is exposed to full manifold pressure. I thus lean towards the second option which seems reasonably straightforward, providing I can get a reasonable seal between the new flexible balance pipe and the hole where it exits the pushrod cover.

I would very much welcome advice from anyone who has solved this in the past.

[Forumadmin]

You can split the engine without removing the heads. So fixing properly is my suggestion.

[ian Howell]

A possible reason for the leak could be that there were apparently different lengths of the centre balance pipe (the bit that links the two ports in the heads and which has 'bulges' near the ends to push against the 'O' ring seals). A shorter balance pipe would cause the leaks as described.

There was correspondence on this subject a few months ago when I think that at least three variants were discovered!

If the engine was rebuilt by someone who had access to parts from previously stripped engines, then the pipes could easily have been mixed up.

[johnairey]

There are two other areas that could be leaking if you think you have a the balance pipe problem. We had a problem with a Severnside members engine that was burning oil and on investigation found that the balance pipe under the push-rod cover had had a section cut out of it and fitted with a rubber hose and jubilee clips and the rubber hose had perished. Replacing the hose solved the problem.

One of seven balance pipes I hold for the section did have a hole in it where it had been fouled by the crankshaft. Five of the seven balance pipes are bent by 1/16 to prevent the foul. The check for foul needs to be made during a trial assembly of the engine when rebuilding an engine.

Re. the length of the seven balance pipes checking over the knuckles maximum difference 1mm. A quick check peak to peak 117mm(4 9/16")

Balance pipe 'O' rings 5/8" I.D.section .100"

[Keith Clements]

Also look under the oil filter as I had a hole there on the pipe to the valve caused by rubbing.