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Piston Size Question
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BIPSBug
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PostPosted: Sat Mar 07, 2009 7:15 am    Post subject: Piston Size Question Reply with quote

Just a quick question. I'm messing out in the garage this morning before I'm dragged off to an Irish festival (ugh) for the day, and I was looking at my new Cylinder and piston I picked up to replace in my older engine I'm rebuilding for my dune buggy.

The engine is an H, and the old pistons(Mahle) read size of 86.93. My new pistons read 85.44. Now I'm wondering if the engine was bored. Will these work? Are the Mahles slightly bigger than the Brailian pistons and cylinders?
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Mark33563
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PostPosted: Sat Mar 07, 2009 7:36 am    Post subject: Reply with quote

you need to measure the bore in the case and the ouside of the jug (cylinder).
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BIPSBug
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PostPosted: Sat Mar 07, 2009 8:12 am    Post subject: Measurements Reply with quote

Okay, the bore in the case measures exactly 90mm.

and the outside of the the jug is 87.5, so....

guess I'll be taking these back next week to get the next size, right? if the bore is 90mm then what size do I need for the piston and cylinders? 90mm?

What those that equate to in horspower? I thought this was a 1500. Its got sp heads that came with it...
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Cusser
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PostPosted: Sat Mar 07, 2009 8:29 am    Post subject: Reply with quote

The sizes on the pistons are the piston diameter in mm, so the ones you purchased were stock 1600cc size (original 83mm pistons for 1500 not readily used these days). Your "H" case was originally a 1500 single port. But if the bore in the case is too large for those, then it's been bored out, like for the 87mm you had in there before, not that uncommon. In other words, someone else already built that engine up for a little more power. So you need to get a replacement 87mm set to fit in the bores you already have.

The 90 and 92mm sets go into larger bores yet.
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Mark33563
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PostPosted: Sat Mar 07, 2009 10:36 am    Post subject: Re: Measurements Reply with quote

BIPSBug wrote:
...i guess I'll be taking these back next week to get the next size, right? if the bore is 90mm then what size do I need for the piston and cylinders? 90mm?

What those that equate to in horspower? I thought this was a 1500. Its got sp heads that came with it...


Take them back and get the ones that will fit the case.

As for the horsepower, it depends more on just the displacement. What cam are you using? Carb? Fuel injected? Turbo? have the heads been reworked? What are the valve sizes? What exhaust? Compression ratio? That is just a few of the questions....

Dual port heads will breathe better. To convert over you will need to replace the two inside case bolts on both sides of the case (total of 4) plus the heads. Everything else is the same with the exception of the intake manifold system and a larger carb (I am using a carb adapter and an early/smaller carb).
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BIPSBug
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PostPosted: Sat Mar 07, 2009 8:50 pm    Post subject: Bores and Cylinders Reply with quote

At least theres no additional cost with 1 step up. Smile Now I can still get those tools I wanted. The heads I'll check tomorrow to see if there looks to be anything special about them.
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kreemoweet
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PostPosted: Sun Mar 08, 2009 8:47 am    Post subject: Reply with quote

90 mm is the stock spigot hole diameter on the 1500 and 1600 cases. Your
85.5 mm P&C set should fit fine.
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