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MG MG Y Type - big end nuts (no, in engine)

Hi all, Need info again. (I am restoring a YT. Body off, to join up the rust holes, chassis replaced , orig too badly bent, and a few other like things.)
And yet another thing.
Have just turned engine over on stand to fit sump gasket and oil seals. But looking at big end nuts shows something worrying. The nuts seem to have a locking ring integral with the nut. But only on half of them is the ring entire. It is either split, or only a portion remains.
Question is, what does this mean, and what if anything do I do now? Engine was running and compression was OK, ages ago when I started to restore the YT.
There were no odd bits of metal in the sump as far as I noticed, though they could of course have been flushed out by oil changes over the years. The picture shows caps on 1 and 2, one has a half ring on one bolt, the other cap shows a split ring.
Regards All, KG

K G Mills

Hi Kevin

If you have not found the bits do not worry - just ensure that you thoroughly flush the engine before reassembly. The bit may well have left the engine with an oil change at some time.

The big end nuts should actually be lock tied with wire. I use an aviation grade wire to wire all the nuts on my engine rebuilds that I do with all the aproproate nuts but inside and outside the engine.

Paul
Paul Barrow

Hi,
thanks Paul. The bolts in my motor aren't drilled, and the nuts aren't castellated so I can't wire them off. One thing I notice as well is this.
The main journal nuts are cottered-off, but one has piece of bent wire. In fact it's visible in the top right of the photo as well. Is that an indication of a bit of indifferent workmanship in your experience?
regards KG
K G Mills

May I put my penny worth in regarding both the big end and small end pinch bolts. The forces on these items is prodigious especially in a long stroke engine, old bolts can actually stretch and eventually fail, if you have any doubt consult a specialist, I recommend Peter Edney who tunes these engines for high performance. Regarding locking wire as Paul says aircraft quality used should be applied with the correct plyers to prevent nicking the wire, in the past I have found bits of wire broken off in the sump. Best of luck Bryan
B Mellem

My suggestion, for what it's worth. New bolts and nuts. I agree with Paul, that wire locking the bolts is probably the best answer. My new bolts arrived with self locking nuts, the one in your photo looks decidedly suspect so I would definitely replace them as well as wire locking the main bearing nuts. I went for the belt and braces approach: self locking nuts, threadlock compound on the bolts plus MGB tab washers. The wrist pin bolts were replaced with socket head cap bolts again, threadlocked, the mains were self locking with threadlock and Tab washers (similar to the one locking camshaft) I don't want a similar event to the one in May, when a rod let go and punched a hole in the water jacket.
If as original, the big end nuts should be 8mm x 1mm a common size, but needing a 13mm socket rather than the 5/16" BSF socket.
Regards
Dave
D P Jones

Hi Kevin,
The main bearing nuts should be lock-wired because, the whole stud could (theoretically) wind out if they are only split-pinned.

Re the big-end nuts .... early cars had castellated nuts with split pins. I wouldn't use wire on big end nuts as the centrifugal force on a few inches of wire is huge compared to 1/4" of exposed split pin end. I have never seen wire used for big end nuts. Later cars had the self locking nuts in your photo. I would have a couple of matching nuts if you want them but I would suggest you only use that system if you are sure the bolts are not stretched or fatigued.

It is probably safer to put in new big-end bolts and nuts. There are good bolts available but I am guessing that some might not be so good. I recommend a Nissan bolt/nut which fits the XPAG engine as if it were made for it. (Rarely, they need the flat on the side of the head ground back a fraction.) The unfortunate thing is that they are not as cheap and available as they were 20 years ago. They fit a '67-'73 Datsun 1300 ute or similar. The part number is 12109-B3000 (bolt) and 12112-B3000 (nut). They were 84 cents each in about 1985 but were several dollars and a "wait for order" more recently. They are a slightly coarser thread than the originals and need to be locked with "Loctite".

Bob Schapel
R L Schapel

This thread was discussed on 05/08/2016

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