Triumph Repair: 76 1500 rattling, piston slap, pin piston

Question
QUESTION: Hi,
  my Spit has a rattling noise that sounds a bit like a nut in a tin can it has done this since i got it 4 years ago.It happens under load only and mostly between 2500 and 3000 rpm curious thing is the noise will get worse if you advance the timing and will be quite a knock,it is not pinging as you can pull away from slow speed in a high gear and there is no noise,it seems i have to set the timing back to keep it from being a really heavy rattling and right now i have it retarded at the best it can be without overheating or sputtering on pull away.Spoke to my Nephew in England who is a mechanic and when posed with the question he said sounds like small ends (wrist pins)his reply was without hesitation "if it gets worse when you advance then it's small ends".Would be nice to get an expert opinion also.
   Regards,Barry

ANSWER: Hi Barry,

First any rattling noise is doing damage and if not attended to, it will do more damage and possibly destroy the engine totally if allowed to continue.

I would first make sure it is not just detonation which you already have done with your tests. Sometimes you can pin point which cylinder by running the engine at the RPM that it is most heard and kill each cylinder one at a time by shorting out it's spark plug. Don't pull the plug wire off to do the "Kill" test because you can then cause a spark to jump down the coil tower to the primary and destroy the ignition module.

When you find which cylinder it is remove the valve cover and check the valve lash on those two valves and the rockers and rocker shaft.

Look at the oil pressure when the oil is warm. (a longer run then getting the coolant warm)

It can be a wrist pin, piston slap or even a badly worn ring grove or a broken ring land if the oil pressure was good. 35 PSI at idle and 45 to 70 PSI at 2000 RPM with hot oil.

I have even found things in-bedded in the top of the piston that got past the air filter or dropped into the plug hole while changing plugs.

Howard

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

QUESTION: Hi Howard,
         thanks for the reply.The noise is only there under load and shows up between 2500 and 3000 as you accelerate,my oil pressure is not as good as it should be but i have no evidence it was ever rebuilt and has recently hit the deadly 60,000 miles.Oil pressure at start is 70-75lbs when hot it will idle at around 20lbs it's about 40lbs when hot at 2000 rpm riding around town but when i drive at highway speed and it is good and hot the oil pressure will drop to 32lbs with 20-50 oil.
 Thanks,Barry

ANSWER: Your oil pressure is a little low with 20-50 oil but still not low enough to cause a rod or main rattle noise. Try the cylinder kill test to isolate the noise to a cylinder. Then if you can call around to fine a shop with a "Bore scope" to look in that combustion chamber to see if any foreign object is stuck in the top of the piston and for the amount of carbon build up. Carbon build up can cause such a noise. If it is determined to be carbon, it is easily removed without removing the head. Let me know if there is a high amount of carbon and I will go over the procedure.

Howard

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

QUESTION: Hi Howard,
         to be honest the motor is quiet at idle and when you rev it with no load so i can't tell which one would be making noise.How do you do the kill test then if you can't remove the plug leads?
 Thanks,Barry

Answer
You can take a 12v test light sharp probe and attach a ground clip to the sharp metal probe and probe each plug cover to short out that cylinder. Then rev the engine to see if the noise is there or not on each cylinder. If just revving the the engine don't produce the noise you may need to have some one in the car and rev the engine with it in a high gear and try to take off thus producing a great load but if you do it that way you must wait a long time between each cylinder test because you will over heat the clutch and burn it out if you test all four cylinders in a short time. Or call around to find a local shop that has a dyno to test on. But that may be expensive. Or you can fabricate a insulated board with four wires that are each attached to a plug wire and while climbing a steep hill have a passenger short each cylinder with a grounded test lead while listening to the noise.

If you can get it to make the noise just by revving the engine just find a shop with a scope as they can do a cylinder kill test electronically. This is not usually expensive. Around here it is from $35. to $50. at the most.

Howard