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MG MGB Technical - connecting rod oil hole,again!
|After reading the BBS archives about this subject, I believe the professional engine builders, & mechanics have it correct, the oil squirt hole goes to the cam side of a MGB engine. I have been an ASE & Land Rover Master mechanic, and have all ways installed the squirt hole to the cam side of the engine. They did it wrong on the assembly line! (IMO.) Also an oil hole on the cam side will lubricate the major thrust face of the cylinder wall.|
Here are quotes from "Automotive Engine Design" by William H. Crouse.
"on some applications",,,.a hole is drilled on one side to the connecting rod" "This hole is called a spit hole because, as the crankshaft rotates within the bearing, an oil passage hole in the crankshaft indexes with this hole. Oil feeds through so that for a moment oil spits, or streams, from the hole in the connecting rod. This oil is thrown against the cylinder wall to provide additional cylinder-wall lubrication. The holes are arranged to index just as the piston approaches TDC (top dead center); thus, a large area of the cylinder wall is covered with oil."
This being said, inspect the location of the oil hole in the crankshaft, it is positioned to line up with the connecting rod spit hole at TDC, only when the rod is installed with the hole towards the camshaft.
Now let's hear pro&con from this excelent BBS group.
While many engine designers sought to reduce wear of the bore, rings, and piston by distributing side thrust forces over as large an area as possible, as in the case of engines having a large bore coupled with a short stroke, the attendant loss of thermal efficiency resulting from the accompanying large roof of the combustion chamber was deemed to be inefficient by the designers of the B Series engine. Instead, lubrication was seen to be the proper solution. In order to accomplish this, connecting rods with the uncommon feature of an oil squirt passage were devised. Contrary to what some amateur engine builders may believe, positioning the connecting rods so that the oil squirt passages face toward the camshaft is not necessary as the camshaft receives excellent lubrication from both the pressure galleries in which its journals spin plus residual oil flowing down the pushrod bores from the rocker arm assembles, as well as oil sprayed from the crankshaft’s main bearings and the connecting rod big end bearings on the crankshaft. When installed, the oil squirt passage of each of the connecting rods must face toward the side of the engine opposite to the camshaft in order to both cool the piston and better lubricate the load bearing surfaces during the power stroke. Failure to do this will eventually result in extreme wrist (gudgeon) pin wear within the piston itself, plus create the very real likelihood of piston failure, not to mention consequent increased bore wear as well.
|Len. I support Steve's, and the factory's, position. I pulled down the engine of my daughter's 77B before she went off to college. As far as we can tell (the car is well documented and we are the third owners) the engine had never been rebuilt. The cylinder bores were in excellent condition at just under 100K miles. Sufficiently so that, if she were to remain at home while going to college, all I would have had done is the bad exhaust valve (root cause of pulling the engine) replaced and left it alone. Do not know if the oil hole opposite the camshaft is "right according to the 'experts'" or not. But, it does work quite well.|
|As a professional MGB engine rebuilder, I always fit the conrod so the oil squirt hole faces AWAY from the cam.|
With the B series engine that rotates clockwise the thrust side of the bore is on the opposite side to the camshaft.
The squirt hole indexes with TWO drillings in the crank big end journal (hole AWAY from camshaft) once halfway on the way up and once halfway on the way down.
Fitted with hole away from camshaft the oil won't reach the thrust side at TDC and won't even get in the bore on the second hole.
The oil is directed at the thrust side of the piston to lubricate the bore as well as throw oil over the gudgeon pins bosses of the piston where there are holes drilled to allow that oil to reach the pin. The other job that oil does is to cool the piston crown.
|Chris at Octarine Services|
|Ooops - Fourth sentence should read "Fitted with hole TOWARDS the camshaft ...."|
|Chris at Octarine Services|
|Been there & tried this!!!!! Back around 1980 I talked with Mike Barret(made race cars for M.G. & B/L) & I asked him what would happen if I switched the rods to help lube the cam better. He said that thay put motors together to race with the rods switched. Well I put a NEW short block assem. together that I bought from B/L for a total of $100. with a 1/2 race cam B/L (714)? I think, 9.5 C/R, lighten flywheel,ported head. Ran it for 200,000 miles & pulled the lifters & ck. them at 60,000 miles & thay were pitted, so every 50,000 I changed lifters, like I do now. SO THERE WAS NO GAIN TO SPITTING MORE OIL AT THE CAM! When I pulled the motor apart the pistons were SHOT BAD, bore was still V/G. New std. pistond & cam & away we go. So there is NO WAY I will switch the rods around.|
|I stand corrected, in spite of my research. I was looking for a rebuttal from the best of the best, and that is what I got. Thank you.|
|"Failure to do this will eventually result in extreme wrist (gudgeon) pin wear within the piston itself, plus create the very real likelihood of piston failure, not to mention consequent increased bore wear as well."|
Steve, this is one of the rare occasions that I have to disagree with you. In practice, the oil squirt isn't crucial at all. In fact the mga twin cam engine has no oil holes in the rod bearings nor passages in the rods and it was intended to be a much higher performance higher RPM engine that the plodding pushrods.
Now you may wish to take a cheap shot ;-) and say that the Twin Cam engines never ran long enough to wear out the pistons, but I have seen long service TC engines that had no dire consequence from the lack of skirt oiling.
I have to conclude that this was an idea that was good in theory but really didn't have much pay-off in practice.
|Ford eliminated the rod squirt hole on their 3.3 and 4.1 liter in-line sixs toward the end of their production to save a few cents. The idea being there was enough splash off the rod journals to lubricate the pistons and cam.|
It worked fine for warm weather locations but they had a lot of recalls in cold climates due to piston pin failures and piston/cylinder scoring. Seems they didn't get enough flow at startup when the weather was cold. I don't think they had any cam/lifter issues.
Obviously a different engine than MG's but it does show that engineers and designers don't always make the right choices. Experience still is valuable.
Since I own a Twincam myself, that's a load off of my mind. I know that the factory ran Twincam connecting rods in their three-main-bearing MGB engines, but I also knew that they rebuilt their engine far more often than we would with our street-oriented engines. Like the other posters, I still feel that the oil squirt holes is worthwhile in the light of experience. You spoke of having seen "long service TC engines". How many miles did they have on their OE pistons?
|HEhehehe - not many - they are infamous for burning holes in the piston crown - possibly due to the absence of a little more cooling from below?|
|Chris at Octarine Services|
The Twincam's infamous problem of burning holes in the crowns of its pistons was ultimately traced to harmonic vibration causing the fuel in the floatbowls to froth, resulting in an extremely lean mixture. The problem was cured by using Misab plates to mount the carburetors on rubber doughnuts, thus isolating them from the worst of the vibration. I've got a set on my Twincam engine, and preignition is not a problem. I just wonder how long the pistons will last without the oil squirt hole in the connecting rods!?
This thread was discussed between 08/02/2009 and 12/02/2009
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