Author Topic: Parts Needed gaskets and piston rings for a longstroke A7  (Read 314 times)

Offline fido

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Does anyone know where I can buy gaskets and piston rings for a longstroke A7? I have a 1948 parts book but if I do Google searches for parts (eg. head gasket 67-28) I only get nonsense answers. I know people like SRM don't do longstroke stuff. I don't yet know what size pistons I have as I can't find my vernier.

Offline Swarfcut

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Re: Parts Needed
« Reply #1 on: 19.07. 2021 19:42 »
fido. I'd recommend ebay.co.uk There are several folks with head gaskets for sale at this time, and established sellers are also offering pistons. Draganfly in the UK have an online parts catalogue, Longstoke parts are hidden within the more modern stuff. Autocycle in the UK still have a range of Longstroke Piston Rings, they are on ebay.

 Don't forget the early parts lists on this Forum, they take some getting used to compared with the modern publications but the information is all there.

 Swarfy.

Offline muskrat

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Re: Parts Needed
« Reply #2 on: 19.07. 2021 21:12 »
G'day fido.
When searching for part numbers like 67-28 add two 00's before the 28, 67-0028. Google that # gets https://tinyurl.com/amnantkb
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline trevinoz

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Re: Parts Needed
« Reply #3 on: 19.07. 2021 22:54 »
Pre unit Triumph 500cc rings will do the job.

Offline fido

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Re: Parts Needed
« Reply #4 on: 23.07. 2021 10:21 »
Thanks for the replies. It looks like Draganfly sell gasket sets and rings. Not sure if I should buy any crankshaft shims as I won't know if I need them until I put it back together. Draganfly say something about the oil rings needing a modification to the piston to deepen the grooves. I'm wondering if these rings were used by the previous owner as they were seized in the grooves. The pistons have the piled arms punched in them so they are genuine BSA.

Online Greybeard

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Re: Parts Needed
« Reply #5 on: 23.07. 2021 12:50 »
Thanks for the replies. It looks like Draganfly sell gasket sets and rings. Not sure if I should buy any crankshaft shims as I won't know if I need them until I put it back together. Draganfly say something about the oil rings needing a modification to the piston to deepen the grooves. I'm wondering if these rings were used by the previous owner as they were seized in the grooves. The pistons have the piled arms punched in them so they are genuine BSA.
I'd buy the shims, they cannot cost very much. If you have them you will not need them. If you do not have them..... guess the next part. 😁
Greybeard (Neil)
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A Distinguished Gentleman Riding his 1955 Plunger Golden Flash

Offline Swarfcut

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Re: Parts Needed
« Reply #6 on: 23.07. 2021 18:06 »
 Fido. A few thoughts about crank shims.

     Longstroke Crank has a drive side ball race BSA Part 67-1240. This is an Imperial size bearing,  Shaft 1 1/8", OD 2 13/16"  Width 13/16" The later roller type bearing is a different size, 30x62x16 mm. They are different shaft sizes but if considered necessary the shims from the later engine would just about do.  Longstroke shaft is 28.575mm, very slightly smaller than the later cranks and I can't see crank shims listed in the BSA  Longstoke parts section.
     Tightening the cush drive on a Longstroke locks the bearing against the crank as usual and as the bearing is a deep ball race type, there is no float other than that manufactured tolerance within the bearing. So looks as if crank shimming is not required to the precision of the later design, featuring a single lipped roller bearing allowing float. Suggested limit before tightening everything up is 5-10 Thou (0.1-0.3mm) for the Longstroke crank. In my estimation until the cush is tightened the shaft must move easily within the inner race.....I doubt this happens in practice and the simple answer is to replace any exiting shims.

 BSA missed a trick with the ball race design here, as there is nothing to hold the outer race into the crankcase other than the press fit. In other words friction and luck. The later design does not put a sideways (axial) load towards the timing side onto the outer race, which would tend to draw the whole bearing from the crankcase as is the case with the deep groove race.

 Ball Race 67 1240 is omitted from BSA Service Sheets, so not readily cross referenced to commercial brands but from the size shown a replacement can be found if required.. C3 Grade usually used in this operating situation if a choice is offered.

 The pistons you have with a BSA stamp should also have reference number. There is a piston chart in the Longstroke Parts book, 1949, in the Forum Literature section and the piston can be identified. Thanks to JulianS for originally posting this valuable reference.

 Old stock  original rings are a better choice than their more modern copies.  Original Hepolite, COVMO  or Milemaster were the favoured brands when the bikes were in daily use and will fit straight from the pack. Ebay is a good source.

 Swarfy.

Offline fido

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Re: Parts Needed
« Reply #7 on: 07.09. 2021 17:04 »

 The pistons you have with a BSA stamp should also have reference number. There is a piston chart in the Longstroke Parts book, 1949, in the Forum Literature section and the piston can be identified. Thanks to JulianS for originally posting this valuable reference.

 Old stock  original rings are a better choice than their more modern copies.  Original Hepolite, COVMO  or Milemaster were the favoured brands when the bikes were in daily use and will fit straight from the pack. Ebay is a good source.

 Swarfy.

Yes, my pistons are marked 67-196 but I can't find that in the parts book. I finally bought a new vernier today and the piston measures 61.6mm. would that make it +20? The book does not give sizes. I'm now wondering if 67-196 is just a number for the unmachined piston as it is also present in raised numerals on the inside of the skirt.

Online JulianS

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This is the piston chart from the 1949 parts book, you can see piston 67 196 on it .

Online chaterlea25

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Hi Fido,
Quote
the piston measures 61.6mm. would that make it +20?

Julian's chart suggests that 67/196 is a standard sized piston  *????*
What size is the bore?

John
1961 Super Rocket
1963 RGS (ongoing)

Offline Swarfcut

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 Fido.    Standard size bore for the Longstroke is 62mm, the piston will be smaller than this to give room for expansion and a running clearance. So from the chart you have a standard size piston, confirmed by your vernier measurement of a 0.4mm less than the 62mm parent bore.

 Measuring the bore should give 62mm in an unworn section.  Piston chart sadly does not  give the compression ratio for your piston. It is rare to find engines still on standard size, but original STD size ring sets are still available on ebay UK and seem more common than the more often required oversizes.

Swarfy

Offline fido

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Thanks for the replies. I can't get that chart to load because my internet is barely working these days. I was going by my hard copy of the 1948 parts book so I suppose these pistons were not introduced until 1949. I suspect my bike has been built up out of parts discarded from other projects! Most parts have been repaired in some way. The bottom of the bore measures 61.8mm but there is a witness mark from a gudgeon pin scraping the bore. It could be the bores were honed at some point to remove that or other damage.