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D7 rebore
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saab9002
Chandlers ford
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February 10, 2021 - 3:27 pm
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Good afternoon everyone,

My question is, how big can you go in reboring a D7 barrel and what piston could you use?

regards and thanks

Chris

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Sponge
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February 10, 2021 - 4:36 pm
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saab9002 said
Good afternoon everyone,

My question is, how big can you go in reboring a D7 barrel and what piston could you use?

regards and thanks

Chris  

I know that you can get to +60 but finding a flat top piston at that size  might be a challenge. Not impossible though. I have seen D7 pistons at +10, +20, +30 and +40 but not bigger.

 You can fit a domed piston at +60 from a D10/D14/B175 but it would require a D10 onwards head....you will certainly also need to play games with the carb jets etc. 

Depending upon how much meat there is on the barrell skirt it should be possible to go out to a 185cc Suzuki piston. Others on this forum have done it and can, no doubt, add more information. 

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saab9002
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February 15, 2021 - 5:09 pm
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Thanks sponge, I've been looking into the Suzuki 185 idea and just waiting for a local company to derust the 

barrel and then I'll have a measure up and see what I can get away withlaugh, but I don't want it to be so

powerful it outpaces my friend's Ducatiwow

regards Chris

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saab9002
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February 22, 2021 - 5:55 pm
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Hi again,

 I’ve had a measure up and have currently a +0.020” piston in, the bore measures ok with very minimal wear but at some time 

previously to my ownership the piston has “picked-up” and slightly damaged the ring grooves. My first idea was to buy another

+0.20” piston and liking the 3 ring pistons advertised by the 3 “biggest” suppliers of parts but it seems that it’s either standard or +0.40”

or bigger but not +0.020”idunno does someone have any idea why ?

regards Chris

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Stoo63
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February 22, 2021 - 6:42 pm
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part number 90-1312 here

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 '55 D3 Battery; '58 Square Four (project); '59 D1 direct lighting plunger; '59 Tiger Cub; '60 5TA;  '76 FS1-E; '91 GTR 1000;  '97 Honda Sky SGX50.

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saab9002
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February 23, 2021 - 9:30 am
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Stoo63 said
part number 90-1312 here

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Thanks Stoo63,

I've had a look and this is only for the ring set not the piston, and further down their list shows the piston set and rings for standard, +0.040"

and +0.060" but not +0.020".

I guess that makes 4 suppliers dunno 

Looks like it might be another rebore !

regards Chris

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Stoo63
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February 23, 2021 - 9:58 am
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Sorry Chris, thought it was only rings you were looking for. Must be a +20, D7 piston out there somewhere..... they made millions of 'em...

 '55 D3 Battery; '58 Square Four (project); '59 D1 direct lighting plunger; '59 Tiger Cub; '60 5TA;  '76 FS1-E; '91 GTR 1000;  '97 Honda Sky SGX50.

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FitzFortune
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February 23, 2021 - 10:09 am
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Chris,

Would this be of any help? It would still leave +40 and +60 as options for the future.

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 - Ian (aka Fitz)

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saab9002
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February 23, 2021 - 11:51 pm
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FitzFortune said
Chris,

Would this be of any help? It would still leave +40 and +60 as options for the future.

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 - Ian (aka Fitz)  

Hi Ian,

I think you're right and I'll give Rex a bell tomorrow, the only thing I noticed was that it's advertised as 62.1mm which I think I could hone out to ,but the piston is stamped 62.9mm, so I'll get that cleared up within the phone call.

As an aside Rex was the only supplier who bothered to reply non-generically to me about the original 3 ring +20 piston set, the others were either dismissive or couldn't be bothered.

regards Chris

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