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68mm pistons
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Author:  Mattywill [ Fri Feb 16, 2018 7:56 pm ]
Post subject:  68mm pistons

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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Author:  aaron [ Fri Feb 16, 2018 8:25 pm ]
Post subject:  Re: 68mm pistons

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.

Author:  drmini in aust [ Fri Feb 16, 2018 9:03 pm ]
Post subject:  Re: 68mm pistons

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.

Author:  Mattywill [ Fri Feb 16, 2018 9:18 pm ]
Post subject:  Re: 68mm pistons

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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Author:  Quick 850 [ Fri Feb 16, 2018 9:42 pm ]
Post subject:  Re: 68mm pistons

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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Author:  drmini in aust [ Sat Feb 17, 2018 5:22 am ]
Post subject:  Re: 68mm pistons

If boring to +.100" or less just straight bore it.

Author:  Mattywill [ Sat Feb 17, 2018 6:54 am ]
Post subject:  Re: 68mm pistons

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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Author:  drmini in aust [ Sat Feb 17, 2018 7:16 am ]
Post subject:  Re: 68mm pistons

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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