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MG Car Repair/1951 MG TD that froze up a couple of weeks ago

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1951 MG TD
1951 MG TD  
Barrie I communicatede with you a couple of weeks a go about my 1951 MG TD USA Car that froze up driving home from a show. I just want ed to let you know what I found. The 3rd cylinder connecting rod appears to have failed. It was not do to oil as all of the other con bearings were in excellent condition and nice an shinny as they were getting oil. The crank on the third cylinder was was burn badly and when the rod went it put about a .40 cgouge in the crank bearing surface. The crank is junk as it is way to far to repair. I am still not totally sure what cause the problem but I am rebuilding the engine as e we speak. I am assuming at this point it was a bolt in the connecting rod that let go. It is almost the only thing it could have been. I ordered a new crank, pistons, connecting rods and bearings and the block is also being machined. If you ahve any insight into what you think might have caused it would be great. I know some times pre-ignition can cause con rod failure but it did not appear to be pre-ignition.

Answer
Hi Mike.

I agree with you - I do not think that pre-ignition was the culprit.  

Also, unless a big end bolt has actually failed, I do not think that was the problem either.  However, you should examine the bolts carefully because the threaded ends do tend to stretch and this is a pre-cursor to failure.

It is a peculiarity of the XPAG engine that con rod #3 tends to be the one that fails.  Usually it is the wrist pin that fractures due to lack of lubrication, but in your case it was the big end that seized first.  You were lucky.  A wrist pin failure usually destroys the block.  

The oil supply to the centre main bearing is shared between journals #2 and #3 so I would guess that something blocked the oilway beyond that point, starving t he journal and causing it to seize solid.

If you examine the drilling in the crankshaft from the centre main bearing to journal #3 you will probably find the culprit still lurking there.  Often it is a small lump of silicone sealant which has worked its way into the journal and blocked it.  The lesson to learn from this is to use silicone sealants very sparingly.

Such a shame.

Barrie

MG Car Repair

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Barrie Jones

Expertise

MG Sports Cars from 1949 to 1980 - Including MGB, MGBGT V8, TF1500, TF, TD and modern Midgets. I also specialise in SU carburettors, Lucas wiring, suspension, steering & brakes.

Experience

I have owned my 1955 TF1500 since 1966. Technical specialist for the TD and TF with the MG Car Club T Register. Also owned 20 MGBs and currently own an MGBGT V8. Written 3 books on MGs and produced a DVD on how to strip and rebuild the TD/TF gearbox.

Organizations
MG Car Club.

Publications
Barrie's Notes on the 1953-55 MG TF (author). /=====/ Barrie's Notes on the MGB (author). /=====/ Barrie's Notes on the MGB GT V8 (author). /=====/ The Essential Buyer's Guide to the MG TD, TF and TF1500. (author)

Education/Credentials
M Phil, C Eng, BSc (Eng).

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