PlastiGage and Some Issues

As some of you know, I pulled the head off my TR4A and decided to replace the pistons and liners. I've had some good help from several folks here, including a cautious suggestion that I use PlastiGage on the connecting rod bearings. I did, but now I'm puzzled.

The bearings show .001 oversize, but using PlastiGage shows that I'm under the spec clearance by about .001.

The spec clearance for the connecting rod bearings in my manual reads .0027, and the allowable play is .005.

PlastiGage says my clearance is barely .001.

Is there a trick to using this stuff, or do I suspect someone put oversize bearings in the engine but didn't cut the crank. I can't imagine that.

I checked all four bearings, and all appear below spec. One nice fat PlastiGage line, well over 1/8 inch thick. Squished out in sort of an oblong fashion.

My oil pressure has always been a bit high, like about 75, and even after warming up it stays around 60.

Any ideas here?

I want to order new bearings, but I can't 'till I figure this out. Three of my four sets of bearings are near perfect. One looks like some grit must have come thru the oil galley, because the middle of it is deeply scared. The crank is only slightly scored on that journel and not enough to warrant yanking the crank imho.

[BTW, I know I need to change the silly "handle" I use. Been too lazy. It's a small town in Nova Scotia where we're from, and "Hound" was either me or our golden retriever we had, whichever way my brothers felt at the time]

Look for a number on the back of the bearing shells. If not there, just get a micrometer and check crank size. However, some experience is required to get an accurate reading with the mic, and not scratch the crank. After you do the rod journals, you will also know what to use for the mains.

Also, if it was mine, I would have marked the shells as to where they came from, so I could put them back where they came from, and I would re use the old ones. A scratch like you are talking about has little affect on oil pressure, as you have seen. If you have that kind of oil pressure, why mess with a good thing? Todays parts sometimes leave alot to be desired, the lower risk would be using the old ones.

Kentvillehound said:

The bearings show .001 oversize,

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Are you saying they are marked 001 on the back ? That would be an undersize; but I've never heard of TRactor motor bearings being available in .001" under.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I checked all four bearings, and all appear below spec. One nice fat PlastiGage line, well over 1/8 inch thick. Squished out in sort of an oblong fashion.[/QUOTE]Plastigage comes in different sizes ... is there any chance you somehow got the wrong size? I don't recall the color coding offhand, maybe someone else knows.<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Any ideas here? [/QUOTE]Only other theory I have is that the crank has been turned before, and left slightly oversize. Perhaps the grinder left an allowance for polishing and then it didn't get polished, or something. I have heard of people polishing them by hand in the car, but it's not a job I'd want to tackle.

Maybe you should just leave well enough alone, and put back the old bearings (after making sure there are no high spots around that groove).

TheSearcherMan said:

After you do the rod journals, you will also know what to use for the mains.

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Not necessarily. I've seen lots of cranks with different undersizes on rods & mains.

Plasti-gage...

green .001"-.003"
red .002"-.006"
blue .004"-.009"

:thumbsup:

My comments are from a professional point of view. What amateurs do are what amateurs do.

It was late. Allow me to try again:

My rod bearings are stamped on the back: 010. I accidentally said 001.

The PlastiGage I used was both red and green. I tried to see if it would make any difference since the clearance by the manual is .0028, and the scales at that spec nearly overlap for each color of PlastiGage--and I kept showing inadequate clearance.

Using red or green, I'm showing a clearance below spec, and I think about .002, maximum.

For instance, using red, I was slightly larger than the largest bar, which is .002. Even assuming it was exactly .002, that would be .0008 too small.

I think I've got no choice but to replace the bearings on the one rod where they are scored badly. The scoring is right dead center in the bearing shell, as if coming from the oil hole in the crank.

About the clearance and the PlastiGage, I suppose I could try using a mic. I'm not sure I want to seal it back up with this clearance mystery, though the car has run great for 4 years now.

Thanks for whatever other help you can offer. I'll be back on the road prior to November. It's all a grand hobby.

Where are you getting the 0.0028" info from?? I'm assuming you're talking about the TR4A. Never mind, I just found that info in a Clymer book...but, that's not what my TR3 Service Instruction Manual says. It gives clearances on the con rod a 0.0016"-0.0035" when new. When I got my engine back from the machinist, and I assembled it, I plasti-gaged the the rods at 0.002" and the mains at 0.0015".

Put it back together.

Re: PlastiGage -- I See Something

I found the receipts where the prior owner had the engine rebuilt. There are entries for new rod bearings (.010)and main bearings, and a $20 charge for "Polish Crank." I see no entry for having the Crank cut for the oversized bearings which are in the engine.

I better mic it, right?

Actually, maybe I'll pull the engine and have an even better time. Can it be pulled without going in through the interior transmission cover and pulling out the seats and carpet, yanking the transmission back, and all that? I can do it; just wondering. I've got a transmission jack, and I'm thinking I could just take the block off the mounts that way.

Also, doing things this way will make it easier to service the cam if needed, and when I clean the block I won't need to worry about getting junk down onto the crank.

On the other hand maybe I'm just looking for excuses to buy some tools. After all, I've been driving for 4 years.

Re: PlastiGage -- I See Something

You have 60PSI when warm!!!! Unless the bearings have some distinct sign of a problem, just put it all back together and DRIVE like you just stole it.

TheSearcherMan said:

My comments are from a professional point of view.

Click to expand...

And I've seen "professionals" bore just one cylinder oversize!

martx-5 said:

Never mind, I just found that info in a Clymer book...but, that's not what my TR3 Service Instruction Manual says.

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Something rotten somewhere. I'm comparing the TR4 factory manual to the TR3 factory manual. They give identical specs for both crankpin diameter (2.0861 - 2.0866) and for con rod bore (2.2327 - 2.2335). The TR3 version additionally gives bearing internal diameter as 2.0882 - 2.0895); which matches the new clearance of .0016" - .0035".

But, the TR4 manual says the clearance is .0028" - .0040"

So either the book is wrong (which wouldn't be the first time), or they started supplying thinner bearings for the TR4 without changing the part number.

Anyway, it worked before. If it were me, I'd put it back together and drive it!

The engine can definitely be pulled with the gearbox still attached. Which probably means you can do it without removing the tunnel (by unbolting the rear crossmember) but I've never tried that.

There is a trick to using Plastigauge. After torquing the bearing cap to spec, remove the cap and, with your fingernail, remove the excess Plastigauge. What will be left is the residue and this is what you measure. That residue will be a little tougher to remove with the fingernail, this is what you want to use as your measuring gauge.

I don't recall reading anything about residue and excess material. What I have gets so smashed and squashed I don't think "excess" or "residue" will come into play.

As best I can tell, my crank is right about spec, at 2.08 inches, maybe 2.075, and that wouldn't seem to have warranted to .010 bearings I have.

I'll figure this out one day soon.

Kentvillehound said:

As best I can tell, my crank is right about spec, at 2.08 inches, maybe 2.075, and that wouldn't seem to have warranted to .010 bearings I have.

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Err, actually, 2.076" is larger than 2.075"; and still a few tenths too small for .010" under.

They never turned the crank. They just used 10 over bearings to take up the wear.
To do this right you need to have the crank turned and new bearings fitted.
Sorry--
Nova Scotia to Arizona--that musta taken some adjustment-
Emmett

I think Emmett is right. What do you think, Randall? They just stuck the oversized bearings on, and that's why I have 75 to 85 psi, or higher, on start up. And barely .001 plastigage clearance.