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



Rob H

Well Known and Active Website User
VOC Member
#1
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 Website User
VOC Member
#2
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

Well Known and Active Website User
VOC Member
#3
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 Website User
VOC Member
#4
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 Website User
VOC Member
#5
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 Website User
VOC Member
#6
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 Website User
VOC Member
#7
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 Website User
VOC Member
#10
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
 

Nigel Spaxman

Well Known and Active Website User
VOC Member
#13
I have been thinking about blocking mine to get more oil going to the cams. In my engine the inlet lobe on the rear cam is the main wear problem and that is the one that shares it's oil supply with the rear piston. What I am reading here suggests it would be a good idea. There are a lot of people who have blocked those holes with no detriment. I have not read any stories ever of anyone having problems from blocking those holes.
 

Rob H

Well Known and Active Website User
VOC Member
#14
My next question would be............Since the rebuild, have you re-torqued the heads.
No not yet, I was waiting to get a good run in to warm the engine thoroughly. At the moment just doing short runs round the houses to sort the odd oil leak now that the flooding of the carbs has been sorted.

Any recommendations or tips on retorquing?
 

greg brillus

Well Known and Active Website User
VOC Member
#15
You need to back off the cylinder head bracket nuts and lock-nuts a small amount (easier to remove tank for a more easy job) I use to use a spring scale and pull with a ring/open end spanner, but now I just back off one head nut a bit and pull up firmly with an open end spanner about 10 inches long and only do one at a time. You will find they will definitely come down by up to 1/8th of a turn but usually less. Put a small black mark with a texter pen on the nut, washer, head before you re-torque, and you will see how much they come down by. Good also to nip up the pushrod tube gland nuts and check the tappets too. The reason that you back each one off a little first is so you have a "Rolling torque" rather than a dead pull from where the nut is now, this gives a much better tension on the hold down studs. Cheers..............Greg.
 

Marcus Bowden

Well Known and Active Website User
VOC Member
#16
Nigel Spaxman said
I have been thinking about blocking mine to get more oil going to the cams. In my engine the inlet lobe on the rear cam is the main wear problem and that is the one that shares it's oil supply with the rear piston. What I am reading here suggests it would be a good idea. There are a lot of people who have blocked those holes with no detriment. I have not read any stories ever of anyone having problems from blocking those holes.

Nigel my handsome, fit an extra pump.
Over 300k on same MK 2 cams, first 100k 5 to 10 thou worn next 200k 2 to 4 thou.So they will see me out Because I fitted a Honda oil p/p and have a constant 0.5 to 1.0 bar pressure squirting through cams onto stelited followers.
bananaman
 

Robert Watson

Well Known and Active Website User
VOC Member
#17
I have used just plain and very thin paper gaskets. I have never retourqued a head and not ever had a leak. One engine has about 70K miles since it was last done. What am I doing wrong?
 

Rob H

Well Known and Active Website User
VOC Member
#18
Checked the head nuts and some were a bit loose so tank was off and head re-tightened, hopefully thats it sorted now.
 

greg brillus

Well Known and Active Website User
VOC Member
#20
Even with the use of the stock thin paper base gasket, the heads will still pull down after the engine has been up to operating temperature. I would not say that Robert has done anything wrong by not re-torquing the heads, but as I served my time as a mechanic as did Bill and several others on here, we were taught to re torque cylinder heads on cars and other vehicles. It is one of the tricks of the trade that almost certainly saves the premature failure of head gaskets on at least some vehicles. It is a habit that i still use and will always use. You could carry out the practice of over-torquing the head nuts like Terry Prince does, as he pulls them down to 45 Lb's plus, his theory that once the bike/engine leaves his shop that the owners will never re-torque the heads again. I don't subscribe to that practice at all, it is a near guaranty of failure, the cylinder studs and columns through the head and the barrel are not designed to take that much load, it will either pull the threads from the crankcase, and/or damage the head. Just my views..............
 


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