Triumph Repair: Spit 1500 engine., spitfire 1500, main bearing

Question
QUESTION: Hi Scott, I found a tight spot on the crank of my 78 Spitfire 1500 while turning the engine over by hand. I was investigating a slow starter motor. This occurs with clutch both in and out and the fanbelt removed. There is also a squeeking noise associated when the tight area comes around. What do you think is causing this - big end, main bearing or something else maybe. I have good oil pressure and no strange knocking sounds with the engine running.
Thanks in advance, Alan.

ANSWER: Is the spot actually binding more than normal compression would warrant?

On the bad side of things, I would lean towards a spun bearing or bent rod or crank.

On the good side, it might be something with the timing chain tensioner, a valve spring or oil seal rubbing;  

Since you don't say where you are hearing the noise from, I would suggest getting an automotive stethoscope and see if you can narrow down where the noise is coming from.

Hope that helps.

---------- FOLLOW-UP ----------

QUESTION: Thanks Scott, i forgot to mention that the engine had been re-built just prior to my buying the car and now has about 2000 miles on it. The noise is definitely coming from the bottom end. Hopefully its timing chain related rather than a spun bearing. If its a bearing can this be replaced through the sump or am i looking at a full tear down.
Thanks for your help - greatly appreciated.
Regards,
Alan.


Answer
Both main bearngs can be replaced from the underside with keeping the crank in the car, but it is tricky, as you could score the journal if you aren't slow and methodical.  

I would hate to say, but it is unlikely that the timing chain is binding enough to cause a drag on the rotation; it is more likely the crank.   I could be wrong.  Since pulling the timing cover would be the easiest thing to do, I would go there first, pull the pulley and timing cover, and spin the crank to see if the "squeek" is now louder, or gone, and whether it still binds, now that the timing cover is off.  If gone, inspect the timing cover for a rub point, or  a tensioner that has worn through.

if not that, then I would pull the sump, and use the stethoscope to see if I can pinpoint which bearing is the squeeky one before pulling anything apart.  Replacing the bearing may not be enough to fix it, as you may have to determine why is it squeeking; i.e. wrong size bearing, journal not ground to correct size, too little clearance when they bored/sized the crank, if that kind of rebuild was done...