• Welcome to the website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Hon. Editor and Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this website.

    If you have previously registered to use this forum, you should log in now. CLICK HERE.

    If you have never registered to use this website before, please CLICK HERE.

E: Engine Curved cam followers



vibrac

Well Known and Active Website User
VOC Member
#1
I re read again all those Big port notes just added by Graham the 'Prof' confirms what I always maintained 1-1/4- 1-5/16 is about right for circuit racing but thats not my main interest hidden away in the screed was a coment about a special cam with curved followers, well, I have a set of those the cam is without a wheel so I cant at the drop of a hat find out the resultant openings anyone else have info
I am having a bit of trouble getting my photos from my android today anyone would think I had an ipad!
 

Bill Thomas

Well Known and Active Website User
VOC Member
#2
I run those square cams in my Special, Not been inside since 1980, When I fitted them.
A few months ago I had to go in there for a stripped Fibre Pinion "D" ign', And change the Breather Spindle.
Can't remember how I timed them in 1980, But now I time a twin by the slot in the end of the shaft, Rear one showing in the middle of the pushrod tubes, Facing upwards, With out turning the motor the front one vertical at the bottom, Facing downwards.
I found the rear one miles out !!, But thought it has much power !, So left it as is.
Cheers Bill.
 

vibrac

Well Known and Active Website User
VOC Member
#3
Thanks Bill very opertune I have to time a twin next week, no 'time' is a bad choice I have to see if the valves touch the pistons and I want to check its not miles out before or rather before I spend time fitting the base gaskets push rod sealing accuratly timing it and all the other gubbins. So one between the push rods at TDC and one pointing down seem an eminently good way to press up some plasticene with a couple of turns.
As for that funny cam and rounded followers we shall have to see when I get back to the racing Comet, However thats sitting about 4th Vincent in my list without counting the other bikes I am afraid but if you have a set they must be of a known advantage....
 

Bill Thomas

Well Known and Active Website User
VOC Member
#5
I like them, they don't "Clack" like standard ones do when you turn the engine over. I didn't get time to fit them 'till I stopped racing the Special so I have never been speed timed with them.
Cheers Bill.
 
Last edited by a moderator:

Bill Thomas

Well Known and Active Website User
VOC Member
#7
Just a thought, Have you got the pushrods to go with them, I think they are shorter ?.
I think mine were Alloy with steel ends. Cheers Bill.
 

greg brillus

Well Known and Active Website User
VOC Member
#8
My understanding is the radius followers act like a "Roller follower" to reduce the savageness of the opening and closing of the valves. The timing of which should not change in reality.......... I have only had experience with those that Terry Prince sells, and his specs are to set the timing on the inlet valve at a certain amount of lift with the piston set at TDC. I would start with our usual method of equal lift inlet and exhaust with the crank at 4 degrees BTDC thus giving the cams an advanced setting. Bill may be right about the pushrod length, on the racer I had to have shorter ones made, and because they are shorter, they are harder to install and I used something like a piece of plastic straw to hang onto them. You might find it much quicker and easier to fit the pistons without the rings on, the barrels minus any base gasket, and fit the head with a couple of washers and hold down nuts ........ So no pushrod tubes to get in the way, this so you can check everything much easier. If you press the rear cam into the pinion only about half way, you can carry out the valve timing and piston clearance checks fairly quickly to see if you are going to encounter any issues, and the cam/pinion can be altered again much easier if the pinion is not pressed on fully. The piston/valve clearance can be done easily given you need to disassemble very little to remove the head without the pushrod tubes getting in the way. Once you get some results then you can aim to finish things off correctly and the base gaskets will give you another 6 to 8 thou extra piston clearance. It is possible that the radiused followers can lift high enough to clip the bottom of the pushrod tubes, especially if the cams have a lot of lift, this is easy to check, again whilst all the "Loose assembly work" is being carried out. Cheers and good luck .........Greg.
 

Glenliman

Well Known and Active Website User
VOC Member
#9
Terry's instructions that came with my radiused follower MK 5s ( first batch 5 yrs ago now?) for the 1360 were to set for equal lift, 3-4 degrees btdc.
In fact, he said " That's the only way to do it"
It worked well, very happy engine.


Glen
 

timetraveller

Well Known and Active Website User
VOC Member
#10
The pushrods are shorter and I got some made fifty plus years ago. I got details of an American firm who will make them any length you want about four months ago. The way I timed them up was to do a full graph of the valve lift against engine position. I can look those graphs out if anyone wishes. I never had any trouble with clashing between the bottom of the push rod tubes and the cam followers but the cams I used only gave a little more lift than Mk IIs. The way to get more lift is eccentric rockers, rather than just on the cam in my opinion.
 

vibrac

Well Known and Active Website User
VOC Member
#12
My understanding is the radius followers act like a "Roller follower" to reduce the savageness of the opening and closing of the valves. The timing of which should not change in reality.......... I have only had experience with those that Terry Prince sells, and his specs are to set the timing on the inlet valve at a certain amount of lift with the piston set at TDC. I would start with our usual method of equal lift inlet and exhaust with the crank at 4 degrees BTDC thus giving the cams an advanced setting. Bill may be right about the pushrod length, on the racer I had to have shorter ones made, and because they are shorter, they are harder to install and I used something like a piece of plastic straw to hang onto them. You might find it much quicker and easier to fit the pistons without the rings on, the barrels minus any base gasket, and fit the head with a couple of washers and hold down nuts ........ So no pushrod tubes to get in the way, this so you can check everything much easier. If you press the rear cam into the pinion only about half way, you can carry out the valve timing and piston clearance checks fairly quickly to see if you are going to encounter any issues, and the cam/pinion can be altered again much easier if the pinion is not pressed on fully. The piston/valve clearance can be done easily given you need to disassemble very little to remove the head without the pushrod tubes getting in the way. Once you get some results then you can aim to finish things off correctly and the base gaskets will give you another 6 to 8 thou extra piston clearance. It is possible that the radiused followers can lift high enough to clip the bottom of the pushrod tubes, especially if the cams have a lot of lift, this is easy to check, again whilst all the "Loose assembly work" is being carried out. Cheers and good luck .........Greg.
Fortunately the twin engine I am going to loose assemble next week is with MK2 cams it's the modified pistons I need to check.
I think it was Ron Kemp or one of the elders and wise ones of the 60's who had a cam wheel that a cam could press into by hand and secure with a low locktite grade to check its effect on the timing and clearances before being removed by a bit of heat, further modified or inserted in its real wheel.
 
Last edited by a moderator:


Top