17 replies to this topic

[MaryQuant88]

Yamaha R1 is a 998 right? so whats stopping me fitting these pistons to my 998cc?
Will These Fit a Mini engine?
Will they be better than other pistons you can buy?

If not What are the best pistons for a 998cc?

:wales:

[The Matt]

998 may be achieved in a different way (ie different sized bores and stroke to achieve the same capacity) so they might not fit.

Infact I'd be amazed if Yamaha got 998 from the same stroke as a mini engine, it wouldn't be much of a revver if they did!

[Bungle]

whats the bore of a r1 and a 998 mini ?

[The Matt]

whats the bore of a r1 and a 998 mini ?

77mm bore, 53.6mm stroke.

So a definite no. :wink:

[The Matt]

oooo, though the later ones were 74mm by 58mm!

Pistons might fit mine! lol

[The Matt]

lol, I got that the wrong way round! The later ones were shorter stroke!

[Oldskoolbaby]

But were the pistons still 74 mm? Im sure Bill Richards builds his 8 ports using 73mm bike pistons. Its not just a case of fitting them to the average A series conrods though. Longer custom made ones are needed to bring the top of the piston up to the top of the block.

[MaryQuant88]

This Topic just shows how good my engine knowledge is :grin:

or the lack of it more like it

:wales:

[MAGA7INE]

Minispares now make fab 998 pistons under the mega brand at large oversizes. They should take any punishment you can dish out to them

[Dan]

But were the pistons still 74 mm? Im sure Bill Richards builds his 8 ports using 73mm bike pistons. Its not just a case of fitting them to the average A series conrods though. Longer custom made ones are needed to bring the top of the piston up to the top of the block.

Those are in a 1275 block though, you can't bore a 998 block that large or it will fall apart.

[Sprocket]

But were the pistons still 74 mm? Im sure Bill Richards builds his 8 ports using 73mm bike pistons. Its not just a case of fitting them to the average A series conrods though. Longer custom made ones are needed to bring the top of the piston up to the top of the block.

Those are in a 1275 block though, you can't bore a 998 block that large or it will fall apart.

Ive seen a 850 block bored to 68mm. Any one gone further than this

[MAGA7INE]

But were the pistons still 74 mm? Im sure Bill Richards builds his 8 ports using 73mm bike pistons. Its not just a case of fitting them to the average A series conrods though. Longer custom made ones are needed to bring the top of the piston up to the top of the block.

Those are in a 1275 block though, you can't bore a 998 block that large or it will fall apart.

Ive seen a 850 block bored to 68mm. Any one gone further than this

I am having a 998 block bored to 70mm to take hillman imp pistons....

[Wil_h]

Minispares now make fab 998 pistons under the mega brand at large oversizes. They should take any punishment you can dish out to them

I didn't know that, but just checked the website, and they're expecting them this month.

Sadly they're all flat tops.

Wil

[Guess-Works.com]

But were the pistons still 74 mm? Im sure Bill Richards builds his 8 ports using 73mm bike pistons. Its not just a case of fitting them to the average A series conrods though. Longer custom made ones are needed to bring the top of the piston up to the top of the block.

Those are in a 1275 block though, you can't bore a 998 block that large or it will fall apart.

Ive seen a 850 block bored to 68mm. Any one gone further than this

I am having a 998 block bored to 70mm to take hillman imp pistons....

Just to add to this..

Dont forget that Cooper S engines are bored out small bore blocks... !

Which is why there aint many of them left

[mini1071s]

Just to add to this..

Dont forget that Cooper S engines are bored out small bore blocks... !

Which is why there aint many of them left

The 1275 cooper block is a totally different casting to the 850 blocks. Among the many obvious visual differences, including completely different main bearings, oil pump, crank configuration, (can't swap an 850 crank into a 1275 block can you?), high tensile studs instead of bolts for the mains, core thickness, they also have completely different deck thickness.

You can machine an early cooper block deck from std down to the size required for a 970 short stroke crank, try that with the 850 block. Cooper blocks have a 5/8 inch deck.

The only time an 850 block was rumoured to be used in any other capacity engine, it was in early 1098s where is was supposed to be bored to the 998 bore.

You must have been thinking of those.

Page 370, Vizard's book in 3rd edition covers all this and more