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MG MG Y Type - My two stroke YB

Hi all
A slight exaggeration but not much. When I recently had harder valves and new guides I also increased the c/r to 8.6:1 which I expect some of you have also done.However soon after this I became aware of a knock/thump coming from the engine particularly at low speed and light throttle.
After much deliberation and discussion I decided to strip and rebuild the engine(it needed doing anyway). The rough noise was still there, only when under light load not when revved while stationary.
I have tried re-torquing the head, moving the timing (worse when advanced and changing the distributor all to no avail. I can however make it much worse by tightening the rear gearbox mount so I think it may be to do with this aspect of the set up.
The compression is good on all cylinders (about 150lbs and the engine runs and pulls well.
Have any of you had a similar problem and if so what was your remedy.
Any other ideas would be much appreciated.
Regards
Brian Hough


B R HOUGH

I don't suppose its the dynamo against the body panel [wrong fan belt], or somehow the engine is twisting on its mounting under load so contacting some other parts.
B Mellem

Brian - was your crank checked for a) size and b) ovalation on your rebuild? What was it oversized to?

I recently had exactly the same experience with my 2002 Dodge (knocking at low revs etc.) ... and it ended up terminal.

Paul
Paul Barrow

Brian, I recently had the pleasure of riding in your YB and hearing the sound you describe, yes it does sound like a two-stroke engine. I'm not convinced that the noise is mechanical i.e. dynamo or crank knowing the thoroughness of the machinist the crank/bearings would be spot on.
My line of thought is on the tightening of the rear engine mount, maybe the exhaust is being put under some sort of strain causing the problem.

As you know, I had a similar problem before I had the water in the oil situation. My thoughts on dismantling the engine, was a certain amount of leakage between 2 & 3 cylinders as there was some staining on the head gasket.


my engine is now ready to go back in after machining, including new liners, crank polished and new mains and big ends, head skimming (-0.003") top of block skimmed (-0.005") to confirm flatness.
Let you know further results when Y4002 is fully back together.
Dave
D P Jones

Hi All

Having still got the 'two stroking' I have been searching the archives and some time ago on this forum there were several of you complaining of a similar problem and the consensus seemed at least in part to be due to the gearbox mounting rubbers being too hard.

I think that might be the problem with Demelza (YB1506) exacerbated by the higher compression (8.6). so my question is has anyone found a cure other than using an old pair of softer rubbers. Perhaps one of the suppliers has the softer mountings or some modification might have been used, or have those effected learned to live with the 'drumming' at certain speeds?

Hoping for a miracle cue!

Regards
Brian Hough
B R HOUGH

hi Brian, on my car someone had assembled the gearbox vertical steady {between the two rubbers}incorrectly, it was metal to metal and caused lots of noise inside the cab but when reving the engine from under the bonnet it all sounded fine. Also my exhaust front pipe was pressing on the clutch cable, hope you find the problem,Graham
Graham Sharpe

This thread was discussed between 21/05/2015 and 15/07/2015

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