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Advice please on what this could be..

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RedTR3

RedTR3

Jedi Trainee
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This is a good-running TR3, Head was rebuilt shortly after I purchased it so top end is good. But ever since I have owned it (3 years) the engine is what I consider to be noisy and it has a "thump-thump-thump" sound at speed that I think I can actually feel. I suspect there may be some bottom end problem. I tried Aweman's trick of unplugging the spark plug wires in sequence and listening, and when I unplug the #4 wire the noise appears to ago away, at least at idle.

Oil pressure has always been excellent, 50-70 lbs.

I suppose you can call me dumb but I have driven the car about 4000 miles in 3 years with this noise...

Realistically I only want to get about another 20K miles max on this car. If it is a bad connecting rod bearing, can this be replaced without engine removal?

I have a good shop that could do this but I wanted to get some expert advice here first.

Thanks, Tim
 
Generally, rod knocks are a sharper noise; a "thump" sounds more like a main bearing to me.

But, the main beaing inserts can also be changed (one at a time) with the engine in the car, so I'd still drop the pan to see what's going on. Even if the crank surface is damaged, some new inserts should help it live awhile longer.
 
TR3Driver is right, good access with the pan off but resealing everything (front/rear seal) is less 'fun' when on ones back. Does save a ton of labor though.
I'd get with some other 3 types (club?) and compare 'noises' before diving in though. Hate to do unwarrented work.
Whats the build number of your small mouth? I've a '56.
 
My car actually has the build # of a TR3A: TS29837LO, but it has the mouth and doors of a '56. Some previous owner somehow combined 2 cars into one. However it is registered with the DMV as a '56, how that happened I do not know. I sometimes call the car FrankenTR.
 
Why not try an engine stethiscope to see if the noise is coming from the bottom end, or higher up the block. With your good oil pressure, it could be just piston slap. The rear piston runs the hottest, and is therefore the one most likely to come under suspicion. If so, it's usually not an urgent repair job as they're a tough old donk.
 
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