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 Post subject: 68mm pistons
PostPosted: Fri Feb 16, 2018 7:56 pm 
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848cc
848cc

Joined: Fri Dec 29, 2017 12:51 am
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Hey all, the 1100 that was 60thou over has been pulled down and sent to the local engine recon guys. They say it’s outside tolerances and we either scrap the block or go 80 thou over with 68mm GR pistons. I’m keen to go with 68mm but my dad is concerned with overheating and reliability. Anyone built a 1098 with GR pistons please comment on reliability? It’s not a race engine but a weekend driver on club plates.
Thanks Matt


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 Post subject: Re: 68mm pistons
PostPosted: Fri Feb 16, 2018 8:25 pm 
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1275cc
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Joined: Thu May 13, 2004 4:41 pm
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Location: sydney
68mm will need more than just a rebore. However, 80" or 100" over are perfectly fine. Don't go overboard on cam and head mods and you wil have a nice Weekend driver.

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 Post subject: Re: 68mm pistons
PostPosted: Fri Feb 16, 2018 9:03 pm 
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Joined: Fri Mar 19, 2004 6:19 pm
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Location: near Baulkham Hills, NSW
I have built 4 motors with 68 mm bore.
68 mm needs the bores offset, a 1275 gasket and some water holes moved to suit it. Bore it to +080 or +100, no such problems.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank @7000+, 45 Dellorto, RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. Going harder with Stealth Black Box in.:mrgreen:


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 Post subject: Re: 68mm pistons
PostPosted: Fri Feb 16, 2018 9:18 pm 
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848cc
848cc

Joined: Fri Dec 29, 2017 12:51 am
Posts: 12
Thanks guys, 12g295 head., cooper ground crank? LCB extractors, hi lift rockers. I’d like some more advice around boring the block? Offset cylinders?


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 Post subject: Re: 68mm pistons
PostPosted: Fri Feb 16, 2018 9:42 pm 
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848cc
848cc

Joined: Thu Jan 11, 2018 8:45 pm
Posts: 2
Mattywill wrote:
Hey all, the 1100 that was 60thou over has been pulled down and sent to the local engine recon guys. They say it’s outside tolerances and we either scrap the block or go 80 thou over with 68mm GR pistons. I’m keen to go with 68mm but my dad is concerned with overheating and reliability. Anyone built a 1098 with GR pistons please comment on reliability? It’s not a race engine but a weekend driver on club plates.
Thanks Matt


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Hi mate i std bore block if you need one call me 0428410636

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 Post subject: Re: 68mm pistons
PostPosted: Sat Feb 17, 2018 5:22 am 
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Joined: Fri Mar 19, 2004 6:19 pm
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Location: near Baulkham Hills, NSW
If boring to +.100" or less just straight bore it.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank @7000+, 45 Dellorto, RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. Going harder with Stealth Black Box in.:mrgreen:


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 Post subject: Re: 68mm pistons
PostPosted: Sat Feb 17, 2018 6:54 am 
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848cc
848cc

Joined: Fri Dec 29, 2017 12:51 am
Posts: 12
Ok guys thanks heaps. We should be able to go again. We have a few spares if it’s completely shot.


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 Post subject: Re: 68mm pistons
PostPosted: Sat Feb 17, 2018 7:16 am 
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Joined: Fri Mar 19, 2004 6:19 pm
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Location: near Baulkham Hills, NSW
Note that 68mm is +.133" oversize from standard 998 and 1098 bore.
So boring to +.080" and +.100" is no big deal.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank @7000+, 45 Dellorto, RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. Going harder with Stealth Black Box in.:mrgreen:


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