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#33883 - 01/28/08 4:10 pm 1960 A10 Piston/Ring Clearances?  
Joined: Jun 2004
Posts: 20
Wyn Offline
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Wyn  Offline
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Joined: Jun 2004
Posts: 20
Buffalo, NY
Hey Gang, Just received .060 pistons and rings from SRM Engineering. They are 7.5:1 compression. My engine is a DA10R (Super Rocket) I just want to confirm, what I want as far as clearance goes, when I talk to the engine borer. It has .040 in there now. The Haynes manual states .004-.0055 piston clearance for a Super Rocket with 8.5:1 pistons.
Setting them to .0045" would be good then? States the comp. rings at .013" and the oil ring at .011".
Do you ALL agree with those specs? Would appreciate your thoughts. I don't want to screw this up. LOL Thanks, Wyn

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#33884 - 01/28/08 10:23 pm Re: 1960 A10 Piston/Ring Clearances?  
Joined: Feb 2004
Posts: 1,956
norbsa48503 Offline
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norbsa48503  Offline
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Joined: Feb 2004
Posts: 1,956
Flint,Mich
Wyn, you need to know the type of alloy they are cast from. (Talk to manf.),some low expansion stock could safely have you running .003 and some drop forged jobs may have you needing near .005. From reading here it's better to set the ring gaps to the larger sizes given again talk to the Manf.,no pat answerers sorry.


norbsa
1960 TR6
1963 Super Rocket
1965 650 Star
1966 441
1968 Thunderbolt
1969 Twinkle 250
1972 Fastback
1974 Roadster
1970 S.S
Way too many BSA's not named
http://decentcycles.com
#33885 - 01/28/08 10:37 pm Re: 1960 A10 Piston/Ring Clearances?  
Joined: Mar 2005
Posts: 731
ca7a Offline
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ca7a  Offline
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Joined: Mar 2005
Posts: 731
Asheville, North Carolina
Piston clearances sort of depend on manufacturer's specification. SRM should provide you with that info. Rings, too.
Otherwise, I'm sure some very knowledgeable forum folks will chime in, Wyn.

#33886 - 01/28/08 11:37 pm Re: 1960 A10 Piston/Ring Clearances?  
Joined: Jun 2004
Posts: 20
Wyn Offline
BritBike Forum
Wyn  Offline
BritBike Forum

Joined: Jun 2004
Posts: 20
Buffalo, NY
There is absolutely NO mfg. markings on the pistons at all. The only markings are on the top of the piston and show 060. I've emailed SRM twice about any specs they might have, and have gotten no answer
since thrs. These damn pistons aren't cheap, but even more, I just want to do it right the first time. The two pistons just came in two plain brown
boxes with no markings at all.

#33887 - 01/28/08 11:57 pm Re: 1960 A10 Piston/Ring Clearances?  
Joined: Feb 2004
Posts: 1,956
norbsa48503 Offline
BritBike Forum member
norbsa48503  Offline
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Joined: Feb 2004
Posts: 1,956
Flint,Mich
Wyn, Can you tell if they are cast or forged pistons. This will narrow it a little, a picture might help. You have to find what the metal is to know so we need some help to identify them.


norbsa
1960 TR6
1963 Super Rocket
1965 650 Star
1966 441
1968 Thunderbolt
1969 Twinkle 250
1972 Fastback
1974 Roadster
1970 S.S
Way too many BSA's not named
http://decentcycles.com
#33888 - 01/29/08 1:41 pm Re: 1960 A10 Piston/Ring Clearances?  
Joined: Jun 2004
Posts: 20
Wyn Offline
BritBike Forum
Wyn  Offline
BritBike Forum

Joined: Jun 2004
Posts: 20
Buffalo, NY
Thanks for the input guys. I just received a reply from SRM on fitting the pistons to the bore. I'm going to take this email reply, along with the spec sheet from Haynes, give it to the machine shop, and hope for the best. Thanks again, Wyn

Here's their reply:

Hi,
Pistons are of Euro origin, but we always fit Hepolite or equivalent rings, just to make sure.

If bore is finished honed to the correct size, clearance and ring gaps will be correct, just fit and go.

Bore and plateau hone to exactly 71.50mm thats 2.8150" +/- 2 tenths.

Bore size is standard BSA, if bore is finished to this size, whatever make piston you fit, will have the correct clearance, piston manufacturers use different alloys, different thickness alloys, so they know the expansion rates for their piston, so they are all made to suit the stock BSA bore sizes.
It is dangerous to deviate from the BSA bore size and go only for clearances, BSA clearances are for BSA pistons only, and do not apply to any other piston.

Regards Gary


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