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MG MGB Technical - Con rods

I have a set of Maxspeeding conrods which seem well specified and certainly look the business but they do not have a drilling for the piston thrust face spit hole. Anyone any experience of running the "B" engine without this oil feed? Maxspeeding claim it is not necessary but I have my doubts. Your comments most welcome. Jim
jim soutar

Jim, there was a thread on the MG Experience recently about the same thing only it was Pouter connecting rods in this instance. The advice from the engine builders in the group was that its not necessary. I dont think any of the high performance after market rods have the oil hole.
Denis
Denis4

Many thanks Denis. Very helpfull Regards Jim
jim soutar

Necessary? No, probably not.

Desirable? Probably - Rolls Royce go to the bother of running oil pipes up the rods to oil the piston thrust face and cool the piston crown.

Chris at Octarine Services

The mga twin cam rods did not have any provision for squirt oiling the cylinder walls and they gave no signs of any problems as a result.
Bill Spohn

Maybe not cylinder wear but they are renowned for burning pistons - I rebuilt "Ratty's" engine which burnt a hole in number 2 piston.

Don't forget the oil supply is there to cool the piston crown as well!
Chris at Octarine Services

Chris, the piston burning problem had no relation at all to oil spray. It was entirely a detonation issue caused by a lean burn situation.

The factory made a mistake on carb mounting, not on eliminating the oil spray.
Bill Spohn

Thanks for your continued comments on the rod oiler gentlemen. Chris. There is an interesting article on the MG Car Club of Queensland site, its in the Tech Talk section. regarding the very poor advance curves in Lucas distributors. The report is that Twin cams donot burn pistons when the curve is correct. Hope this is of some interest to you. Jim
jim soutar

Yes, I know the twin cam was prone to run lean with the original carb set up because of vibration. Equally the wrong advance curve may over advance the engine. Ratty had correctly mounted carbs and a correct curve but still burnt the piston.

Piston cooling must help the engine survive even in the most adverse of set up conditions - it's absence only makes these things more critical.
Chris at Octarine Services

At the end of the day, a little extra oil in places is centainly not going to do any harm. Yes, I know you don't want oil on your clutch faces! I suppose too many oil holes means your pump has to deliver more and if it does, then it is also drawing power and adding resistance. Think, those piston crowns get really hot, and forged pistons run a little less hot. So have the intention of the engine in mind as you build. Perhaps use non-squirt con rods and forged pistons. Mike
J.M. Doust

Jim, havnt you built that engine yet????

Actually neither have I. It will be interesting to see if the rods really are made out of chocolate?

Anyway I am doing 2 other engines as we speak, using Arrow rods in one and Saenz rods in the other. Neither have the extra oil squirt. So I think I would not be worried about it.
Incidentally what would you think the rev limit would be with steel crank, rods and forged pistons?

Let me know how you go on.

Colin
Colin Parkinson

Mike,

More oil holes simply means that the relief valve passes less oil. The pump will pump exactly the same amount of oil at any given revs whether the oil goes to bearings or back to the sump via the valve!
Chris at Octarine Services

Colin. My engine is now built and installed. Ran for the first time today tho it will be some time before I can run it in and test it on a dyno. ( hopefully on Peters new one) So far it"s beautifully smooth and responsive. I opted to run the Maxspeeding rods without the squirt holes , largely because of the difficulty in getting them drilled accurately. Further research shows that many modern engines do not have such holes, tho I would think that the larg4er bores and in some cases the ofset of the crank in relation to the bores will allow more splash to reach the piston underside. Having considered the comments from Chris and the other members, I do however believe that the "B" engine would be better with the extra oil cooling to the piston and pin, I"ll keep a close watch on things when I do get the car back in service in the spring. Just to be on the safe side I have prepared another 1950 short motor with the requisite oil holes should it all go pear shaped. Jim
jim soutar

Jim, sounds good! I am just doing 2 1840 race engines, then I will get on with my 1950, with the Maxspeeding rods.

Which pistons did you use in the 1950, twin cam?

I am not sure whether to use t/c or bite the bullet and get forged!!

Take care, and have a good christmas

Colin
Colin Parkinson

This thread was discussed between 25/10/2010 and 16/12/2010

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