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Comet cylinder/piston/rings installation

craig

Well Known and Active Website User
VOC Member
what is the technique to installing the cylinder down over ringed piston? Is this method preffered?
Or should i install the piston/rings down the cylinder and let the wrist pin peek ouk for pin install?

If a ring compressor is required, what exact brand and details should i look for? i am not looking for a lecture on piston ring compressors. What would be best are part numbers and websites.
I realize i could use hose clamps.
I realize i could use a roll of shim stock.
I am looking for the professional Vincent mechanic approach, as i will be repeating this several times if not more.

Evidently this is so basic, it is not found in VRH, KTB or VOH

Any help is fantastic, thanks
Craig
F5AB/2A/7090
F5AB/2A/8530
 

Tom Gaynor

Well Known and Active Website User
VOC Member
I tried shim stock, and hose clamps but eventually went back to basics. I didn't have, and was unable to find a bike ring compressor.
First you MUST have a chamfer inside the liner. It doesn't have to be huge, but it HAS to be there. Fit the gasket, but if using Wellseal or the like, leave the top of the gasket clean for now. Then, prop the piston in place with a couple of bits of wood placed either side of the rod on top of the crankcase. That makes the job MUCH easier. A refinement is to put some torque on the crank to keep the piston in contact with your two bits of 1" x 1/2" strip. Slide the barrel down over the piston canting it slightly to "catch" the front of the top ring then the rear.. I chose to have all the ring gaps on the side I was working from so I could push any "loose ends" in to the ring groove with a screwdriver without the acrobatics required to change sides. Then apply Wellseal to the top of the gasket, if using, and drop the barrel into place.
I've done Vincents, Rudges and Manx Nortons all the same way. Use makes master..and I've never broken a ring.
Tom
 

Comet Rider

Well Known and Active Website User
VOC Member
Hi Craig,
The method that we use, involves getting a bit of 2mm thick ally sheet, about 30mm wide, and folding over about 5mm to make a top hat. You will need to cut releifs out of this flange so that it can wrap arround the piston. We use cable ties to hold the clamp on.

Make sure you have a good chamfer on the liner, and also lightly oil the bore.

Best of luck
Neil
 

Albervin

Well Known and Active Website User
VOC Member
I use 2 metal rulers! There was a template in a magazine many years ago for a sheet metal "fork" to aid in the fitting of a Series A barrel (5 studs to deal with) but the metal rulers, oiled bore & a good clean chamfer will do the job. Do Not use "The Force" but
gentle persuasion.
 

ET43

Guest
Hi Folks,
I made a wooden catapult shape that has a slot in it wide enough to pass either side of the con rod, and which will rest on both faces of the crank case. Having a handle too, it can easily be withdrawn after use. I got my ring compressor from Vin Parts. As Tom says, keep slight pressure on the crank to make everything square for the piston to slide into the bore. Lubricate the rings well! Cheers, ET43
 

john998

Well Known and Active Website User
VOC Member
Hello, I use Albervins method, but only use grease the base gasket and so far have had no leaks there.
I must have read the grease idea somewhere in the past, something to do with that joint moving with heat.
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Confession time. I use grease on cylinder base gaskets too. Perhaps if they leaked I'd go to Wellseal, but they haven't.
I always go to considerable lengths to get the two sides of the crankcase top face flat before bolting up, using an oilstone as final proof. This might mean putting head and barrel on, tighterning them down, tightening the crankcase bolts, then taking head and barrel back off to fit piston (an indispensable aid to maximum performance).
The first thing you need is a flat top face, and the second, a crank that turns SLOWLY with no resistance. Don't tighten up until you have both, and once you HAVE tightened up, check again. This might mean shimming to make sure the rod is in the centre of the bore.
As Glen Bewley says: "if it's almost right, it's wrong".

Tom
 

Vic Youel

Well Known and Active Website User
Non-VOC Member
I have found that assembling the piston on the bench (with one gudgeon pin circlip) into the barrel first (with the three gaps at 120 degrees) much safer. The modern oil rings are difficult to compress. Then lower the barrel and piston down on the studs and insert the gudgeon pin.

To prevent dropping the second circlip into the crankcase use a long rod through the gudgeon pin.

Vic
 

tonythecat

Well Known and Active Website User
Non-VOC Member
"To prevent dropping the second circlip into the crankcase use a long rod through the gudgeon pin."

Vic, that's one of the best tips I have heard for a while, thanks.

Tony
 

deejay499

Well Known and Active Website User
VOC Member
Very similar to some of the above. I use a piece of U shaped wood under the piston like Phil, and lower the barrel onto the already fitted piston with ring gaps equally spread. I do not use any oil at all and never had a problem. I was told that this is what the racing boys do to stop the bore glazing on start up. Anyone else do this?

Dave
 

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