Triumph Rat Motorcycle Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter #1
Today I took a long ride up into the hills with some friends on my 1973 750 Tiger… Probably about 100 miles of riding. I return home and notice the oil pressure light is on when I pull in the garage. Rev the bike a little so see if it’s an issue of thin oil… light stays on. Look down at my return line; there’s oil moving there. Long story short: I pull the timing cover off and the crank end seal was ripped. So I was riding with very little pressure. I fixed the seal and the engine built up good pressure and held it for 4 or 5 seconds after killing the warmed engine. No weird noises or other abnormal behavior. How much sleep should I lose over this?
 

·
Registered
Joined
·
6,527 Posts
If you are talking about the small seal that mounts in the timing cover, when I tore my '66 T120R engine apart, that seal was torn. I suspect it happened when the bike was reassembled and would guess that's when yours tore as well. Can't see a seal tearing once properly engaged on the shaft. Wear yes, but not torn.

There were no signs of any abnormal wear in my engine. Looks like it had original bearings, which I replaced due to wear. But there were no indications of overheating of the bearings or wear on the big or small end bearings. The wear I found was typical for usaged/age, not from lack of lube.

I would agree with the others that you are okay.

regards,
Rob
 

·
Registered
Joined
·
38 Posts
Discussion Starter #5
Thanks Snakeoil, 68TR6R, and KADUTZ, I feel much better knowing that others have had this problem and not suffer catastrophic engine damage.

The seal was definitely torn and the spring fell off. It may have been damaged on installation… but I put about 1000 miles on the engine with no oil pressure warnings, so I think it finally gave out yesterday… maybe as I drove away from home with the bike cold and relatively higher oil pressure. In any case, with no seal, I was probably running with 5 pounds of pressure or less in the bottom end… seems like that would cause problems in terms of wear. I’m going to check the exhaust valves and see if they’ve loosened up due to oil starvation on the exhaust side cam.
 

·
Registered
Joined
·
6,527 Posts
Oil pressure is used to get the oil where it is needed. The bearings actually create their own oil wedge as they operate. This is why splash lubricated engines, which have no oil pump run fine with minimal to no wear. I'm sure everyone has seen that old cast iron B&S engine that Gramps had on his first lawnmower that still runs like the day it was purchased and has never been apart.

As long as you had oil coming up thru the return line, you had oil going into the top end. 5 psi seems like a small number but put 5 psi of air pressure in your fuel tank and watch it turn into a nicely deform globe. What you lost was flow. Flow takes heat away from the bearings (and journals in the case of plain bearings). But you had reduce flow, not zero flow so you should be fine. If you had let the bike idle for a half hour in the blazing sun you might have seen issues in the big end bearings. Chances are the problems would have occurred after you shut the engine down and the hot journals heated and possibly melted the babbet. But that's an abnormal condition. I don't think any of us would let an air cooled engine idle for a long period on a hot day.

Your oil pressure switch might be iffy. Might pick up at a lower than normal pressure. Just thinking out loud here.

regards,
Rob
 

·
Registered
Joined
·
38 Posts
Discussion Starter #7
thanks Snakeoil. when you put it like that, i feel better. Maybe I will take the pressure switch out and use my air compresser to determine the psi trigger point. I've read it should be around 7-10 psi. It worries me a little that i revved the bike up to 4000 rpm and the light stayed solid but i checked the exhaust valve clearances and they were correct. if they were loose, i would be concerned that there was cam wear since, as i undestand it, the cam surface is lubricated primarily by the bottom end circuit.
 
1 - 7 of 7 Posts
Top