• 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.

Rebore

Puddle jumper

Well Known and Active Website User
Non-VOC Member
Hi Gang,
Is there a trick to reboring Vincent cylinders, do they have to be clamp on boring plates etc, like I would for a Harley cylinder,
Cheers Paul
 

roy the mechanic

Well Known and Active Website User
VOC Member
If using a conventional boring bar[ Buma or S P S] its the only way to fix barrel to machine. Don't forget to "trap" the top of liner with the top adaptor plate to avoid movement during the work. Be lucky, Roy.
 

timetraveller

Well Known and Active Website User
VOC Member
Unless the job is done by someone who knows his Vincents then you should check the base of the cylinder for perpendicularity to the bore after the job is done. To do this you will need to make something up which fits into the top and bottom of the new bores and allows the muff and liner to be spun in centres. Having checked several at Roy Robertson's then typically you will find about five thou run out on the base and probably the top. The top is not critical but it better if it is correct, the base is super-critical if modern low clearance pistons are to be used. Typical recommendation on these pistons is three thou clearance. If the tilt of the base is for and aft then you might get away with it. If it is side to side you will not.

This festive theme is making me mutter bah, humbug! Crusty old devil!!
 

ET43

Guest
Boring time

Yes Norman, Bah, Double Humbug. I thought that somehow I had on my 3D glasses ( those of you of a certain age will understand ) Roll on the New year when all this Hoo Ha will be over.
Another Grumpy Old B*****r
 

roy the mechanic

Well Known and Active Website User
VOC Member
Time Traveller's point well taken. If proved correct, any material removed from either end of cylinder has to raise compression on those affected. You will then need to calculate the actual compressions to restore equilibrium. Iassume, like me, you would rather run a pair,similar! Regards, Roy.
 

Puddle jumper

Well Known and Active Website User
Non-VOC Member
Is similar close enough !!!!

Hi Roy,
Similar sounds good to me, and to be honest as I think the engine is out of a racer of sorts and it looks like its had plenty of mod’s and a hard life, who knows what I will find when it's stripped down, I do know from what the previous owner said that its only done 150 miles since its last rebuild back in 1961, but he's not sure what was done, he thinks that the bore is plus 0.060" and it's running bigger valves, the reason for the rebuild was that the old girl dropped a valve at speed, ouch.
Must admit I can’t wait to start stripping her down, sounds like lots of fun,
I would like to get the power up to 65 horses at the wheel, should be possible I think.
Cheers Paul
 

timetraveller

Well Known and Active Website User
VOC Member
Yes, I worried about increasing the compression ratio if the base of the muff was reduced so I did a sum. The cylinder head capacity is 103.5cc on my heads and the swept volume is 499cc. Total is 602.5cc. [As an aside if you had a flat topped piston which did not protrude above the top of the liner then one would have a compression ratio of 602.5/103.5 = 5.8 : 1 (there's tractable isn't it?)] To calculate how much volume is contained in one mm of cylinder take a radius of the bore as 4.2cm, square it and multiply by PI and then divide by 10 (1 mm = 0.1cm) I make it that each mm of stroke contains 5.541 cc. Suppose we machine five thou off the base of the muff. Five thou is about one eighth of a mm and so the swept volume of a five thou slice is about 0.69cc. In addition one is not taking a five thou cut off the whole of the base but only of that part which is high so perhaps about half that figure is what will change. Feel free to check the sums and if they are wrong I will go and stand in the corner. :cool:
 

Latest Forum Threads

Can't Find What You Need?

Buyer Beware: Fake or Real?

Top