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Thread Like Summary
Stuart Kirk
Total Likes: 1
Original Post (Thread Starter)
#817559 07/26/2020 10:18 PM
by Richrd
Before this mess hit I had the bike running and was beginning to like it. But on the first trip out of the neighborhood it locked up and took out the crank shells.

I had the crank ground and reassembled it as carefully as I could. WITH AN OIL GAUGE! After a few rides around the neighborhood I went out for about 10 miles. What I find is about 70 psi on start up but as it warms up the pressure drops. It sat at 40 for a couple miles then dropped to 30. I was tip toeing home by then.

So my question, is there something to check? Or just go for a new oil pump?

Liked Replies
#819892 Aug 14th a 12:50 AM
by Tridentman
Richrd must be losing patience over this problem.
Just reading the last few posts I realized that I had lost track of the various happenings on this thread.
So I went back to the beginning and noted the significant developments.
It goes something like this:
a) An incident happened which took out the crank shells.
b) The crank big end and main journals were ground and new shells fitted.
c) At start it gave 70 psi then after a few miles this went down to 40 and then 30.
d) Increasing the revs do not increase the pressure.
e) The OPRV was stripped and examined and found to be OK.
f) Another gage was tried in case the original gage was faulty. The second gage broadly agreed with the first gage.
g) The back of the oil pump was lapped smooth.
h) The pump was tightened back tio the mating surface.
i) It was suggested that the oil feed pipe at the standard T150 5/16" is under sized compared with the later T160 3/8".
j) A new oil feed hose was fitted. At start up it gave 60 psi which then went down to 40. With a blip of the throttle it went down to 30 and then back up to 40. At 2500/3000 rpm the pressure was 35 with idle at 25. With the throttle blipped it went to 30 and then back down to 25.

Having gone through all the above the original problem remains.

What might the problem be?
Some thoughts:
a) What was the problem that "took out" the crank shells? Are we sure we know the cause(s)? Is there debris still lying around in the engine?
b) The oil feed size can be disregarded IMHO. While it is desirable to enlarge the inlet to 3/8" as Triumph did on the later T160s it is not essential to do so. There are literally thousands of T150s running around quite satisfactorily with the 5/16" oil feed pipe size.
c) The OPRV and oil pump seem to have passed inspection so at this stage at least we should I guess rule them out of suspicion.
d) The very strange reduction of pressure with increase in revs (assuming that the pump and OPRV are working OK) points to a supply side restriction causing cavitation within the pump. The fact that the latest test showed an increase in pressure with an increase in revs STARTING AT IDLE is IMHO very significant as cavitation generally starts and gets worse at higher revs-- so the expected behavior of increased pressure with increased revs starting at low revs but not at higher revs is a pointer towards cavitation.
It has been known for hoses to delaminate but this has been ruled out by replacing the oil feed hose. However looking at the supply side of the pump the following questions come to mind:
a) Is the oil tank clean?
b) Is the oil tank oil filter clean?
c) Are there any obstructions within the oil pump on the inlet side?

That is about as far as my analysis takes me.
However answers to the questions posed might help us to move forwards and solve the problem.
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