Triumph Repair: connecting rods, rod bearing, main bearings

Question
QUESTION: A mechanic told me that the bearings on the connecting rods on my TR3 engine are scored and should be replaced, even though the engine only has 5000 miles since a re build in 1994. Can this procedure be done without pulling the engine?
Thanks

ANSWER: Hi Jeff,
I have several problems with what you told me.

1. What prompted this mechanic to tell you this and how did he make this determination?

2. When a rod bearing is scored, most likely the crank is scored and the main bearings are also scored. But it depends on how badly they are scored.

3. How many times in the 5000 miles has the oil and the filter been changed?

4. Did you put the 5000 miles on this car since the engine rebuild?

5. Do you know what was done on the rebuild?

It has been many years since I worked on TR-3s but as I remember there is room to remove the pan from below. Other than just an inspection it would be very rare that you could correct anything by just changing bearings because of what I told you above.

When a rod bearing is scored, it is scored for a reason and since the only oil that gets to a rod bearing has to go past the mains  the mains must have damage also.

99 out of 100 engines that have rod damage also have main damage.
Let me know
Howard

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

QUESTION: Howard, Thanks for the quick response. I was confused by that assessment also. If one is scored, so should everything be. The engine has had three changes of oil, but it had not been driven in three years. The oil pressure has always been low and when it gets above 3500 RPM there is a "clacking" noise. That is what prompted him to look at the bearings. He felt the crank was ok. as were the mains.

Answer
Jeff, No one can determine if a crank is good or bad by feeling it. You can make a rough idea if a crank is ok by the use of "PlastiGage". And if it is used on a crank while still in the car it should be done in two different positions on the crank.

If a crank feels smooth and it is Plastigaged in two directions and the readings are from .001" to .002" with the new bearings, then I agree you could just put bearings in it. If it is checked in two directions it should not be more than .0005" difference. (out of round)

However from what you say "Always noise and low oil pressure" they are indications that the bearings were never correct or you have a pressure regulator valve problem. The pressure regulator valve is in the oil filter block. It is normally set to 70 to 80 PSI.

Oil pressure is built up because the oil can not get past the bearings and pressure builds. When bearing clearance is too excessive the oil runs through the bearings and does not built up much pressure. There is a pressure regulator valve the prevents oil pressure from building too high and if it is stuck open or has a weak or broken spring, the pressure can be low. Under normal conditions on your car with 10w 40 oil and the oil is warm, you should see 25 to 35 PSI on the gauge at idle and from 50 to 80 PSI at cruise speed. Anything less than that indicates something is wrong.

You need to ask your mechanic if he used "PlastiGage" and what the readings were. And if he said he did ask what color he used and if he don't say "green" and the readings were 2 thousandths or under, you need to find a mechanic that knows what "Plastigage-Gage" is and what color to use and how to use it.

Howard