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How to tell if you need bearings or full rebuild

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tdskip

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I think the TR3 ate her motor today. The oil pressure has been low since I bought her (50 to start, about 20-30 when warm, but out on a drive today once warm the pressure dropped to almost zero at 2500 RPM. At idle, when I was shutting her down as quickly as I could without causing an accident, the pressure was essentially zero.

Uh oh....
 
First thing I'd do is confirm the integrity of your oil pressure gauge! Admittedly, though, I'd also be afraid to start the engine again. Disabling the ignition and checking to see if it builds oil pressure might be another thing. But my bet is that, if it didn't go BOOM, or overheat or send up large plumes of smoke, that it's not as deadly serious as one might think....
 
Hi Andy - thanks for the super fast response.

I just cranked her over without the coil connected and she got pressure, so I started her up. She used to run about 50 at idle on the gauge when cold, it is now more like 30 at idle. At 3000 RPM cold I see a bit less than 50, but it looks like her pressure is definitely down from before.
 
If it's really down close to zero pressure (and not a gauge error) I would expect to be able to hear the engine making a lot of noise at least at the top end and particularly when up at 2500 to 3000 rpm.
You have not mentioned it making a noise so I tend to think it isn't terminal.
Easiest & cheapest refresh to the oil pressure is pulling the pan and replacing main/rod bearings, you can do it in-situ on a set of car ramps fairly easily; just keep everything spotless clean.
Let us know how you're getting on.
 
Re: How to tell if you need bearings or full rebui

Before you go nuts check two things.

1) The oil pressure gage, make sure it is working and is accurate.

2) The oil pressure relief valve, it could be sticking and not completely closing.

I had something like what happened to you happen to to in my Tr4 and it turned out to be debris in the oil pressure relief valve. I cleaned it and life was good again. /bcforum/images/%%GRAEMLIN_URL%%/driving.gif
 
AltaKnight said:
If it's really down close to zero pressure (and not a gauge error) I would expect to be able to hear the engine making a lot of noise at least at the top end and particularly when up at 2500 to 3000 rpm.
Click to expand...

Well, she is louder than before but not completely different. She sounds more "tappety", but again not a dramatic change from before.
 
Re: How to tell if you need bearings or full rebui

I've seen filters drop oil pressure in some of my Triumphs. I have had early Spits and a 1500 and a GT6 and sometimes the filter just did not want to cooperate. But, the by-pass is a sure bet which is linked to the filter housing. I started a Jag once and the pressure dropped to 0 after warming up. Took apart the oil filter housing 3 times and even replaced the oil pump when I found a piece of wood from a handle I used to install pistons on rebuild holding the by-pass open.
 
Re: How to tell if you need bearings or full rebui

Merlin63Tr4 said:
Before you go nuts check two things.

2) The oil pressure relief valve, it could be sticking and not completely closing.
Click to expand...

Let me go check the relief valve out.
 
Re: How to tell if you need bearings or full rebui

So I just disassembled the relief valve - which was a first for me - and it looks OK. No gunk or junk in the spring.

I cleaned the spring and assembly and noticed that there was a special kind of washer, that prevented me from tightening adjusting screw any further. Loosening it was easy, but tightening it wasn't possible.

The washer was like an upside down plate, and made of a very soft metal. I tried to reposition it and it started to bend so I stopped and installed the whole assembly.

The adjusting screw is part #91. If I was able to tighten this wouldn't help push the oil pressure up?

The oil pressure did come up a bit after I did this. I'm back to 50 at idle cold, but it doesn't climb any higher at RPM.

TRI-002.gif
 
tdskip said:
Well, she is louder than before but not completely different. She sounds more "tappety", but again not a dramatic change from before.
Click to expand...
Proves nothing, but that is about how I would describe the change in sound when my TR3A lost oil pressure. Nothing dramatic, just seemed like I was hearing some valve noise at freeway speeds when I couldn't before.
 
Re: How to tell if you need bearings or full rebui

tdskip said:
The adjusting screw is part #91. If I was able to tighten this wouldn't help push the oil pressure up?
Click to expand...
Depends entirely on why the pressure is low to begin with. When everything is normal, that screw controls the pressure only when the pump is producing more oil than can flow through the bearings, etc. at the set pressure. But you have apparently had some sort of failure and, unless the failure is the spring broke or suddenly got much weaker; IMO it's not likely that fiddling with the relief valve adjustment will help.

It's been a long time since I was in there, but ISTR there is some sort of seal between the body of the relief valve and the partition in the filter housing. Might that seal have failed ?

Oh, BTW, it's not gunk in the spring that causes problems, it's gunk trapped between the ball & it's seat.
 
One of the things you've got to understand is that oil pressure doesn't protect the engine. All oil pressure does is ensure the oil goes through the passages and holes and gets to the areas where the unpressurized oil is protecting things. The oil in the bearings isn't pressurized, and it's the presense of the oil that is protecting the bearings.

So oil flow is real important, and pressure much less so. That's why engines don't die from momentary loss of oil pressure. It's the longer term loss of flow that kills things.

Sudden drops of oil pressure are typically things like pickup screen blockage, pressure relief spring breakage, cracked tube, etc. Gradual long term dropping of pressure is more indicative of engine wear, oil pump wear, etc.

As for bearings vs a rebuild, that's darn hard to tell from the outside of an engine. You can't measure bore wear and such. Only when you open the engine up can you see how things look.
 
Re: How to tell if you need bearings or full rebui

Yes, pull the pan and post some pics back for us to review.

Check that pickup screen carefully while you're in there.
 
Re: How to tell if you need bearings or full rebui

tdskip, if you are not familar with plastigauge, then you should learn how to use it to measure the clearence between the bearing inserts and the crankshaft journals.
That would be the first place where damage would show up.
 
Re: How to tell if you need bearings or full rebui

I'll have to school myself - this is all new territory for me. But hey, you have to learn sometime, right?

It is going to be a few days before I am able to pull the pan, but thanks for all the help and coaching guys. I really appreciate it.
 
Re: How to tell if you need bearings or full rebui

I have heard on a TR6 about a plug on the end of the rocker shaft that could pop out and cause loss of oil pressure, could that be the problem on a TR3
 
Re: How to tell if you need bearings or full rebui

Where's Don or Randall? I don't know if the TR3 has a plug in that spot.
 
Re: How to tell if you need bearings or full rebui

On the TR3, the ends of the rocker shaft have steel caps that are pinned in place. Not likely to come adrift, tho I suppose it must have happened to someone, sometime (probably due to improper installation).

Furthermore, in both TR3 and TR6, the rocker shaft sees essentially no oil pressure, so loosing an end cap would not cause loss of oil pressure; only loss of oil to the rockers. The exception of course would be if you have fitted the external oil feed to the rocker shaft (which IMO is a Bad Thing but for other reasons).
 
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