Gas in oil conundrum *long post*

[74BGT]

Hi everyone, I posted this in another MG forum, but I wanted to get feedback from members here as well...

I've been diligently doing bodywork on the '74 MGB GT I bought this fall. Yesterday I was getting tired of drilling and chiseling, so I decided to concentrate on mechanical things, which I prefer over metal work. I pulled off and sold the Weber DGV that came with the car. When I took the carb off this fall, the engine only ran on three cylinders. This was fine, I knew it did it and I figured once the bodywork was done I'd go through the ignition system and rebuild a pair of HIF4 carbs and get the engine sorted out. The three cylinders that did fire did so smoothly, although I have never checked compression on the cylinders (need to remember to get my dad's compression gauge next time I go home from college).

Anyway, last evening I went to remove the old Uniparts oil filter and I drained the engine of oil. I noticed that it was flowing very fast for such cold temperatures, and in fact seemed very 'liquid'. I let some splash onto my fingers and the 'oil' was like water, no thickness or viscosity, and smelled like gasoline. When I bought the car, it had been sitting for months excpet for the occasional startup when the previous owner was showing the car to prospective buyers. Six months ago he said he'd been using it regularly, but that the engine had a miss (I think it was probably running on 3 cylinders then too). My theory is that there has been excessive borewash and it's been contaminating the oil. Is this plausible? or should I be searching for other possible culprits...also, the car has been run with very non-viscous oil for God knows how long, probably not too good for the bottom end. Oh well, thoughts and opinions as to how I should approach this?

 

[William]

Any ideas what viscosity oil was being used to start with? I seem to remember that we use 10W30 in the B, and I did so in the Midget, but could go down to 5W if needed.
As for gas in the oil, there's probably been a problem with the carb adjustments, causing it to flood (which could explain the "miss" the PO mentioned. An engine not firing on all cylinders is pretty obvious, and not something most would call a "miss". That's something wrong.). That's the only way I can thing of to get gas mixing with the engine oil. If it's been going on a long time, sure it could build up. Improper starting procedures (running with the choke on too long, or pressing the gas pedal fifty times before cranking) could cause extra gas to get in too.
As for the missing cylinder, I'd make a check to see if there's any damage-pull the head if possible, or look in a sparkplug hole at the top of the piston. It sounds ignition related, but its best to be sure.
Hope this helps!
-William

 

[Bugeye58]

Well, if there is no compression in one cylinder, due perhaps to a bunch of broken rings, all the fuel that went into that hole will find its way straight to the oil pan. That would explain the miss, as well.
This is the worst case scenario, understand. It could be just from sitting so long, with periodic restarts that caused the oil dilution.
Jeff

 

[74BGT]

Thanks all,

I will check compression, and probably will pull the head just to examine the state of things. I can't actually start the car until I rebuild the HIF4 carbs sitting on my workbench and find all the bits to the manifold/linkage to make it complete (I just grabbed all the major bits out of a box in my Dad's garage).

The engine has 120K indicated so some head work may be in order anyway.

 

[Guest]

Another thought . When I first got mine from the PO, it was only running on three cylinders but those three were running good. I didn't have the gas in the oil problem, but it might be worth you looking at before pulling the head. One of my valve adjustments wasn't secured properly and it loosend up and the secureing nut was completely off and on its way toward one of the return oil holes. I put it back together and adjusted the valves and it ran like a champ and the PO said it hadn't run this good since new.

Your miss also could be just a plug wire. Measure the resistance of all four wires and compare. They should be in the ballpark of 5-15K ohms if they are resistor wire. Usually a bad one will be completely open.

I usually try to get the easier less expensive things first but my thoughts usually go to the worse case senario.

If Jeff is right, then you will probably be looking at a scored cylinder too.