E: Engine How critical are the rear cylinder oil feeds!

Rob H

Well Known and Active Forum User
VOC Member
Just got the bike back on the road after fitting new cams and followers did about 40 miles and removed the timing cover to check the seal on the rubbers and that everything was still OK.

Out of curiosity something I did not check when the bike was in bits were the oil feeds though the spindles.

I used a bit of 1mm copper wire to poke down the holes and found the cam spindles OK and the front cylinder through to the crankcase. The oil feed to the rear cylinder seemed to be blocked as the wire would only go in about 40mm. I thought it may be sludge but found it difficult to clean, I even put a small drill down and it was solid. I am starting to think it may have not been drilled properly or someone broke a drill down it.

I am guessing that this has been there all the time since rebuild about 9k miles ago. When I had the top end off there was a little sign of wear on the rear of both pistons but no pick up or seizure.

The question being is how critical is it to have the oil feed to the rear cylinder wall, my current thoughts are to run the bike as is this summer and maybe replace the spindle over the winter .

Any views welcome
regs
 

greg brillus

Well Known and Active Forum User
VOC Member
The holes in the case back into the vertical holes for the threaded cylinder hold down studs, and these have a machined groove around the mid section of the stud to allow the oil to pass around the stud and on to the cylinder liner feeds inboard of there. The are lots of opinions about the use of them or blank them off. I am of the thought that the oil being thrown off the bigend and upward to lubricate the piston skirt and the gudgeon area is a bit limited due to the long stroke design of the engine, so I feel they should be used. The main thing to watch is that the oil holes in the liners are injecting oil bellow the lowest piston ring. A lot of factory liners left with the holes too high, thus injecting oil into the rings and causing oil usage. If this is done correctly, then it should cause no problem.
 

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
1990 rebuild in France did away with oil feeds to cylinders with Alpha Romeo low expansion pistons Honda oil p/p supplying cams 2010 with 118 k miles holed rear piston (20mm) and dropped front Ex V/V seat simultaneously, reason ! one of the twin coils failed and it was suddenly too retarded norm 24 degree with twin plug. But the pistons walls were all good, better idea is oil jet squerting oil under piston crown, bigger Honda p/p coming up.
bananaman.
 

davidd

Well Known and Active Forum User
VOC Member
Rob,

I have never used the cylinder oil holes in any Vincent I have run. I also think the liners are a little long so, I don't disagree with Greg. I don't think the oil holes do any harm when properly installed. I have been using aluminum liners for a few decades now and I have them made short. I have never had piston problems.

I know Patrick Godet puts them in all his bikes.

I have not done a twin in a long time, but on the Comet the spindle can actually hit the right rear crankcase stud. If you have had a crankcase stud out and in your hand it has an interrupted thread. This narrowing of the stud occurs where the spindle is located. The studs are designed to be bottomed in the crankcase because they are designed to pass the oil to the cylinder at this very specific height. If someone did not pay attention to the goop in the bottom of the crankcase stud hole the oil passage cut into the stud may be too high. If it is a little off a wire might be poking that part of the stud that is too high in the hole because it is partially closed off.

In fact, on a Comet you should check the length of the spindle if you are installing a new one because you might not be able to push the spindle in far enough to get it under the steady plate. The last one I installed I had to shorten. I found this yesterday in the parts I was installing:
Spindle.PNG


David
 

Bill Thomas

Well Known and Active Forum User
VOC Member
Another way to check for a blockage, Use a squirt can with oil, You can feel if there is a too much pressure,
I have a Twin Crank , Where there is something wrong, Must strip it out some day, It's under the bench.
 

Rob H

Well Known and Active Forum User
VOC Member
The holes in the case back into the vertical holes for the threaded cylinder hold down studs, and these have a machined groove around the mid section of the stud to allow the oil to pass around the stud and on to the cylinder liner feeds inboard of there. The are lots of opinions about the use of them or blank them off. I am of the thought that the oil being thrown off the bigend and upward to lubricate the piston skirt and the gudgeon area is a bit limited due to the long stroke design of the engine, so I feel they should be used. The main thing to watch is that the oil holes in the liners are injecting oil bellow the lowest piston ring. A lot of factory liners left with the holes too high, thus injecting oil into the rings and causing oil usage. If this is done correctly, then it should cause no problem.

Liners were replaced in the rebuild with lowered oil holes but the hole does not even go as far as the intake follower never mind the stud.
 

Bill Thomas

Well Known and Active Forum User
VOC Member
I would take a chance and leave it, Lots of people have blocked them off, Just don't thrash it.
Cheers Bill.
 

Rob H

Well Known and Active Forum User
VOC Member
That's the plan, I am sure its been like that all the time and done two long long runs on it (800 & 1000 mile) and the pistons and bores still seem to be good.

R
 
Top