MG T-ABC

Hi all
Not strictly TABC (although I have a TC) but an XPAG question regarding my YB that now sounds like a 2 stroke or motor boat.
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

Brian, it sounds to me like you have a metal to metal contact somewhere on the engine/gearbox to chassis. Inspect the rubber bushes on the gear box and engine to see it any have collapsed and the metal is laying on metal.

Can't think of anything else where tightening a mounting changes the sound.

Brian,

Could you possibly have a bolt that's too long connecting the bellhousing to the engine? Under a load the crankshaft will shift backwards slightly and it may just be the tiny amount that would cause interference between the flywheel and one (or more) bolts.

Gene

Hi
Thanks for replies, however this effect started after I had the head worked on. This means it is either a direct result of the head work, some result of say the higher compression or a coincidental effect ie the short engine was not changed until later. It is very difficult to describe an engine noise but it could be described as a cross between a big end problem, a mechanical interference with the engine and frame and an exhaust resonance (frequency lower than the engine note). But having rebuilt the engine I think that it is not the bottom engine. I have changed the distributor and cap with leads, I have changed the coil, rebuilt the front UJ and looked at back wheel bearings. At present I am replacing the head with two gaskets to lower the compression so watch this space!
Regards
Brian Hough