Triumphrat

04-20-2005

Hello fellow RATS,

I'm not getting a good oil seal on my rings for my 71 bonnie tr6. (With the head off i crank the kick-start several times and it will leave oil at the top 1/2 in. of the cylinders). I put in a new set of rings and honed the cylinders with the Sears brand honer. Still poor seal and smoking form both barrels. Question is I'm still at stock +20 on the rings. Can i increase to say +40 rings and keep the same pistons? Or do +40 pistons to go with +40 rings? And at what point do i look into a re bore, or do i have to re bore with upping the ring size. Any info would be greatly appreciated as i feel like a piston ring idiot at this point.....

Thanks, sprintyelf :-g

Slinky · 04-20-2005

It's all related- you need a +40 rebore before you can fit +40 pistons and rings. They all go together.

Did you measure the ring gaps, and stagger the gaps around the bore?

DAGAD · 04-20-2005

First job as Slinky says, measure the bore. Also it is important to stagger the ring gaps. Take the top ring from the piston and set it into the bore about 1" down from the top and check the ring gap, you should have between 0.012" and 0.016". Any more is too much.
At a push, and if the bores are good ie. not oval and not too worn you can "gap down" a set of +0.030" rings to give you 0.014" gap. This will probably get you through this season.
One other thought, have you checked the inlet valve giudes and vales for wear? Roy

squod · 04-20-2005

Dagad scores again :gpst:

04-20-2005

Thanks for the replies,

I've measured the bore and they are both just shy of 2.80 inches. Placing a ring in the cylinder i find the ring gap to be .068 with my feeler gage. Now I'm confused. The bore is just a hair over standard, probably from honing but the rings are not gapping close enough.

Any further suggestions, I'm also looking into the valves.

Thanks a bunch, sprintyelf. :-g

DAGAD · 04-20-2005

Ok, your bores are fine and STANDARD ( 2.797"). I guess someone has fitted rings from either the 500 (T100) or a Trident.
Both of these have a 69mm bore and so +0.020" or +0.040" 69mm rings will fit your ring grooves in the piston but will give you a HUGE gap!
Get some new Apex or Hepolite rings, Glaze-bust the cylindres and don't forget to stagger your gaps! Roy.

panic · 04-20-2005

That's not what he has.
69mm ring fitted in 71mm bore will have .247" end gap: 2mm (bore diff) X .03937" X 3.1416.

[ This message was edited by: panic on 2005-04-28 15:46 ]

squod · 04-20-2005

put oil in it and ride

DAGAD · 04-21-2005

Panic not, I suppose I asked for that one? So using your formulae: 69mm @ +.060" = 70.5mm.
0.5 (71 - 70.5) X 0.394 X 3.142 = 0.06189". Fairly close to Sprintyelfs' 0.068"?
At the end of the day....HE HAS THE WRONG RINGS FITTED! :hammer:

04-28-2005

Thank you all for your replies.
So i took the pistons and cylinders to a local restorer and it looks as though someone prior to me has done somewhat of piss poor job of a piston rebuild. So the rings i put in don't match the bore or the the pistons in a sense (sorry it begins to go over my head at a point). He's got me squared away without too much damaged to the wallet. Were doing a +.020 re-bore with new hepolite pistons/rings That will match the bike 9.1 ratio.

Dagad, Squad, Slinky, thanks a bunch you guys really help the little guy like me pointed in the right direction.

Regards, sprintyelf :-g