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A65 Cylinder measures small #785929 09/30/19 10:11 pm
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Nick H Offline OP
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I finally have the time and funds to get back to my '67 Lightning project and have been doing some measuring of the engine parts.
Stock standard cylinder barrels are 2.95276" (75 mm) according to my sources.
Using my Starrett inside micrometer I'm getting 2.94".
Can anyone explain what may be going on here? They don't appear to be sleeved or altered in any way that I can see.
[Linked Image from i.imgur.com]

Last edited by Nick H; 09/30/19 10:15 pm.

1966 BSA Lightning
(2) 1967 Triumph "Choppa"s
1974 Indian ME125
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Re: A65 Cylinder measures small [Re: Nick H] #785931 09/30/19 10:18 pm
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NickL Online Content
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Maybe it's an A64-3/4.............................
How often do you use an inside mike? A bore gauge may be the answer.

Re: A65 Cylinder measures small [Re: Nick H] #785943 09/30/19 11:46 pm
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Does your inside mic have rounded anvils? Maybe try a piston if theres one handy.


71 Devimead, John Hill, John Holmes A65 750
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Re: A65 Cylinder measures small [Re: Nick H] #785946 10/01/19 12:04 am
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Nick H Offline OP
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I somewhat confirmed the measurement with my dial caliper. I'm getting nearly 13 thousandths of an inch less than 75 mm. Wouldn't think my tools are that far off.
I'll buy standard pistons since I need them anyway and report back.


1966 BSA Lightning
(2) 1967 Triumph "Choppa"s
1974 Indian ME125
Re: A65 Cylinder measures small [Re: Nick H] #785987 10/01/19 4:44 pm
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Interesting

Does this barrel appears to be "used"?

Could it be an A50 barrel someone punch-out?

I would agree with NickL, get a bore gauge and a micrometer and set up @75MM to get more of an accurate reading

or perhaps it left the factory on the tight end of the tolerance?

I suppose I would go to +.020 rather than standard, take into account wear, taper, etc if there is any


[Linked Image from live.staticflickr.com]
Re: A65 Cylinder measures small [Re: Nick H] #785994 10/01/19 5:40 pm
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If its an A50 barrel the fin count will be less, its quite possible its been overbored, 7 on A50 , 8 on A65 , IIRC


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Re: A65 Cylinder measures small [Re: gavin eisler] #786030 10/01/19 10:31 pm
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NickL Online Content
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Originally Posted by gavin eisler
If its an A50 barrel the fin count will be less, its quite possible its been overbored, 7 on A50 , 8 on A65 , IIRC


A50 wont fit the head stud pattern.

Re: A65 Cylinder measures small [Re: Nick H] #786035 10/01/19 10:57 pm
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Well its a weird one then, maybe a 650 rather than the usual 654 cc. For a certain race class maybe.?


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Re: A65 Cylinder measures small [Re: Nick H] #786044 10/02/19 12:21 am
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Nick H Offline OP
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Ok, I'm not that experienced with mic's but on looking at it today, it's maybe a bit larger than I thought but if I set my Starrett to 2.95276" (75mm) - it definitely is less.
This is not a dial gauge I am using. It is an inside micrometer kit made by Starrett and considered highly accurate.
I can check my inside mic with my outside mic and they jive.
I can't swear that the cylinder was ever used but the rest of the motor (crank etc) shows some wear. The bike sat in a collection for some years.

Last edited by Nick H; 10/02/19 12:28 am.

1966 BSA Lightning
(2) 1967 Triumph "Choppa"s
1974 Indian ME125
Re: A65 Cylinder measures small [Re: Nick H] #786064 10/02/19 8:36 am
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The picture is low res but if I blow it up there appear to be thin liners installed, maybe as Gavin suggests it was to enter a 650 class and the std barrel would have disqualified.

Re: A65 Cylinder measures small [Re: Nick H] #787334 10/17/19 7:48 pm
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Nick H Offline OP
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Well, standard pistons arrived and they fit nicely. I'm sorry for the confusion. I don't have a lot of experience with micrometers but I will say this cylinder has no apparent wear.

Now I notice these 2 small holes in the cylinder.
[Linked Image from i.imgur.com]
They are on the exhaust side and match up on the head.
[Linked Image from i.imgur.com]
and protrude through the top next to the valve guides.
[Linked Image from i.imgur.com]
where the opening looks irregular and like a crack almost.

I see the holes in the cylinder in the parts manual but my Haynes manual makes no reference.
What are they?


1966 BSA Lightning
(2) 1967 Triumph "Choppa"s
1974 Indian ME125
Re: A65 Cylinder measures small [Re: Nick H] #787335 10/17/19 8:24 pm
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Look like oil drain holes to me, probably intended to help remove excess oil from the rocker box area and maybe provide some cooling around the exhaust guide area. These holes are often a source of leaks so make sure the head gasket makes full contact in this area, I believe some have managed to use O rings between the head and barrel to seal the holes.

Last edited by gunner; 10/17/19 8:25 pm.

1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: A65 Cylinder measures small [Re: Nick H] #787377 10/18/19 9:51 am
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As gunner states, they are drain holes, the inlets drain down the pushrod tunnel. These are nicely cut, I have dressed them on some of my heads because the holes aren't dressed at all, and there has seemed to be an exccess of oil around the exhaust guides.

O rings work, when repop gaskets are used with large oil holes. If you can get NOS or some of the better made gaskets (beleive theres a chap in the states making them to original spec) then you will find it will seal without o'rings. Also check the head and the barrel for being perfectly flat, often the heads get planed and barrels ignored. They do go out of shape too usually around the mounting studs.


beerchug
Re: A65 Cylinder measures small [Re: Nick H] #787379 10/18/19 11:01 am
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kommando Offline
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Brit Gaskets is Canada based

http://britgaskets.com/bsagask.html

and highly recommended, website is difficult to navigate as 1/2 seems missing.

Re: A65 Cylinder measures small [Re: Nick H] #787385 10/18/19 12:36 pm
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MarcB Online Content
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Steve @ Britgaskets still sells his stuff, but usually only on order. I ordered from him back in March. I don't know that he does head gaskets.


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