Author Topic: a7 piston and crankshaft experts wanted  (Read 1411 times)

Offline edboy

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a7 piston and crankshaft experts wanted
« on: 22.01. 2013 20:45 »
hello,
my a7 is currently bored to 67.5mm or +60. there is loads of meat left and wondered if anyone found c15 pistons or any other type would fit. it would be a shame to bore to 71mm or resleeve.any suggestions welcome.
i also have an early crankshaft with the sludge trap screws milled flat without screwdriver slots which is puzzling me but again if anyone can remind me how the sludge trap fits on the early twins it could save future heartache. i m sure the large journal cranks had a tube but its been a long time.
edboy
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Offline wardleybob

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Re: a7 piston and crankshaft experts wanted
« Reply #1 on: 23.01. 2013 10:08 »
I I
Have had great results with t 150 pistons only trouble is you have to buy three    cheers wardley bob
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Online BSA_54A10

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Re: a7 piston and crankshaft experts wanted
« Reply #2 on: 23.01. 2013 10:11 »
T 150's use the same piston as C 15's.
A 75 owners oft buy a set of Ceefeer rings if they break one during installation.
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Offline andy2565

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Re: a7 piston and crankshaft experts wanted
« Reply #3 on: 23.01. 2013 10:14 »
hi bob
have you found any high comp alternatives fo an a10 ?
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Offline edboy

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Re: a7 piston and crankshaft experts wanted
« Reply #4 on: 23.01. 2013 12:35 »
hi wardley bob and others.
i looked at triumph trident pistons but the triumph has a different hemispherical head shape ,hence very domed piston. also has a smaller gudgeon pin[larger small end bush means more vibration i m warned]. the small end is also nearer the crown than an a10 piston but i dont have a suitable a7 piston to measure and compare so if you have done this conversion already did it fit without machining the crown ?
the reason i asked about c15 pistons is that they have the same dome shape as a7s and might share same small end size.
i have a feeling someones run braze down the sluge trap plugs so i have my work cut out this year.
regards edboy
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Offline muskrat

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Re: a7 piston and crankshaft experts wanted
« Reply #5 on: 23.01. 2013 12:39 »
I used T150 pistons in my A7SS racer. With the different pin height I had to use A10 rods and shorten them a few mm. It also gave it about 14:1 compression for running methanol.
Cheers
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Offline wardleybob

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Re: a7 piston and crankshaft experts wanted
« Reply #6 on: 23.01. 2013 16:46 »
For a10 iused to use datson cheery pistons but they are hard to get now wardley bob
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Offline Slide

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Re: a7 piston and crankshaft experts wanted
« Reply #7 on: 23.01. 2013 20:30 »
Reference sludge trap screws, based on my A7SS small journal crank there is no tube inside as such, just the screws either end that form a seal. If there are no slots you might have to drill a hole in them and  extract them out.. then just flush out the internals and fit new end plugs. I center-punched the edges of the new endplugs on mine a few times to make sure they wouldn't fall out, as I wasn't to confident about relying on threadlock for that..
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Online KiwiGF

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Re: a7 piston and crankshaft experts wanted
« Reply #8 on: 24.01. 2013 05:40 »
Where are you edboy? I ask as i have a barrel in the for sale section. Obviously i was asking too much for it as it has not sold. Just go to the for sale section and type in a7 barrel

Simon
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Offline edboy

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Re: a7 piston and crankshaft experts wanted
« Reply #9 on: 24.01. 2013 21:25 »
hello, thanks for all the positive replys. everyone is helpful.i feel the barrels i have are too good to junk but muskrats suggestion of altering the conrod[or having new ones made] is the way forward for me. i have a set of 68mm pistons in mind to use but i will need to work out a new conrod length. unfortunately an expensive route.
regards edboy
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Offline muskrat

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Re: a7 piston and crankshaft experts wanted
« Reply #10 on: 24.01. 2013 22:22 »
 Compare the pin center to top ring groove will tell you witch way to go. If you go the T150 rout I might have a set of A10 rods already shortened. A10 rods are 0.468" longer than A7 (short stroke).
Cheers.
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Offline edboy

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Re: a7 piston and crankshaft experts wanted
« Reply #11 on: 26.01. 2013 22:59 »
thanks for the offer muskrat but i ve bought a less radical shaped piston which i hope will give about 9/1.the a10 conrod idea seems alright but you must have welded and shaped a new small end to the rod? i think new rods would be stronger and might try thunder engineering later on.
regards edboy
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Offline muskrat

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Re: a7 piston and crankshaft experts wanted
« Reply #12 on: 27.01. 2013 03:11 »
 No worries mate. I took 2 or 3mm (can't remember off hand) off the mating faces of the rod and cap then re-machined the hole.
Let us know the outcome of your mods.
Cheers
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Offline kommando

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Re: a7 piston and crankshaft experts wanted
« Reply #13 on: 27.01. 2013 19:16 »
I fitted a Trident piston to a C!5 and the engine ran well so the crown cannot be too high. Did not have to raise the head/barrrel or remove anything from piston, a B25 piston would be a problem though.
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