• 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.

ET: Engine (Twin) Cams

timetraveller

Well Known and Active Website User
VOC Member
The timing of both is supposed to be identical so there should be no difference in performance but I have measured a large number of cams and have yet to see a quieting ramp on what is supposed to be a Mk III. I cannot say that none of them have ramps but when one measures the lift, takes differences and computes velocity and acceleration, the ramps just do not show up.
 

rapide049

Well Known and Active Website User
VOC Member
I have 2 Twins
The Mk1 will pull on the Hills , The Mk3 I will be back into 3rd gear
the MK3 runs nice but does Not have the same pulling power
Mk1 has Standard Mag and 30mm Mk 11/2 concentrics
Mk3 has BTH Mag and Mk1 30mm Concentrics -(and uses up to 2 litres of less Fuel on a Tank
The Mk 3 is much quiter in the Timing Chest

Hope this makes Sense
Thanks Greg
 

passenger0_0

Well Known and Active Website User
VOC Member
I have 2 Twins
The Mk1 will pull on the Hills , The Mk3 I will be back into 3rd gear
the MK3 runs nice but does Not have the same pulling power
Mk1 has Standard Mag and 30mm Mk 11/2 concentrics
Mk3 has BTH Mag and Mk1 30mm Concentrics -(and uses up to 2 litres of less Fuel on a Tank
The Mk 3 is much quiter in the Timing Chest

Hope this makes Sense
Thanks Greg
Interesting....
I've ridden bikes that go strong and yet on inspection have worn out cams and followers.
I'd be really surprised if the cam profiles between mk1 and Mike coulton felt via a seat of the pants test.
Could the difference you experience be down to other factors aside from cam profile, such as carburation, compression, bore wear, valve seating, etc. ...?
 

greg brillus

Well Known and Active Website User
VOC Member
When I rebuilt my Rapide back in 2016, I had always felt the bike was missing something........it went ok, but the engine felt like it had no real "Life in it"......After the strip down I was surprised to find the pistons were 8:1 compression.........I had always thought it was about 5:1 the way it behaved.........Anyway the cams were original Mk 3's as Greg is asking about.......These were in perfect condition.......During the rebuild, I had what appeared to be some sort of Mk 2 cams, and a set of the highly polished followers that Big Sid sold me. These cams have actually got way more duration than normal Mk 2's, but i used them anyway, and replaced the pistons with new ones again at 8:1 comp........Now the bike goes like a " Raped Ape" so that's good enough for me. To me it is almost like the Mk 3 cams were retarded, certainly not lack of compression like I had always thought.......
 

rapide049

Well Known and Active Website User
VOC Member
Interesting....
I've ridden bikes that go strong and yet on inspection have worn out cams and followers.
I'd be really surprised if the cam profiles between mk1 and Mike coulton felt via a seat of the pants test.
Could the difference you experience be down to other factors aside from cam profile, such as carburation, compression, bore wear, valve seating, etc. ...?
Both are in Top condition , the only difference between them as I have explained
 

rapide049

Well Known and Active Website User
VOC Member
When I rebuilt my Rapide back in 2016, I had always felt the bike was missing something........it went ok, but the engine felt like it had no real "Life in it"......After the strip down I was surprised to find the pistons were 8:1 compression.........I had always thought it was about 5:1 the way it behaved.........Anyway the cams were original Mk 3's as Greg is asking about.......These were in perfect condition.......During the rebuild, I had what appeared to be some sort of Mk 2 cams, and a set of the highly polished followers that Big Sid sold me. These cams have actually got way more duration than normal Mk 2's, but i used them anyway, and replaced the pistons with new ones again at 8:1 comp........Now the bike goes like a " Raped Ape" so that's good enough for me. To me it is almost like the Mk 3 cams were retarded, certainly not lack of compression like I had always thought.......
Greg that is good discription ,it goes ok and everything is New in it , yes it Feels Retarded - thanks for your reply
 

Glenliman

Well Known and Active Website User
VOC Member
I have 2 Twins
The Mk1 will pull on the Hills , The Mk3 I will be back into 3rd gear
the MK3 runs nice but does Not have the same pulling power
Mk1 has Standard Mag and 30mm Mk 11/2 concentrics
Mk3 has BTH Mag and Mk1 30mm Concentrics -(and uses up to 2 litres of less Fuel on a Tank
The Mk 3 is much quiter in the Timing Chest

Hope this makes Sense
Thanks Greg
Do both bikes have the same type of silencer?
The silencer design can make a big difference to power output.

Glen
 

Pushrod Twin

Well Known and Active Website User
VOC Member
Perhaps it is the way the cams have been "timed" when the engines were assembled? If one engine was assembled by someone using the 4Deg BTDC technique, that engine will likely perform well. If the other were assembled by relying on the dots on the cams, it could well have one, or both, cams a tooth advanced or retarded or any other random combination of valve opening & closing times.
To identify the differences between the engines I would suggest you start with compression pressures, which can be difficult enough with a kick starter, but just looking at the piston crowns through the plug hole may be enough to give you a hint? Then compare valve timings between the engines with a degree wheel.
The audible noise from a timing chest has nothing to do with "quietening" ramps, in spite of what is written in the factory publications. If there is a reduction in audible sound between cams with quietening ramps & those without, that is coincidental. Quietening ramps are about letting the valve settle onto its seat gently, 'decelerating" it if you like, to reduce shock loading, wear and seat recession, any reduction in sound that our ears can detect is secondary.
If you have a noisy timing chest, it is not necessarily confirmation of MK I cams, there are plenty of other possible explanations for that.:)
 

Latest Forum Threads

List of Forum Categories

Can't Find What You Need?

Buyer Beware: Fake or Real?

Top