Flex hone Rotax 787

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g68bird
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Flex hone Rotax 787

Post by g68bird »

I have a 2003 2 stroke 787 Rotax engine I'm putting a new set of pistons in, sleeves look in good shape. i need a ball hone and had a few questions.
The ring material is stock, I don't know what they are. Bore size is 3.258 First time doing a 2 stroke. my questions are..

1.What grit hone?
2. What size hone?
3.What hone material?

Thanks.
BillK
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Re: Flex hone Rotax 787

Post by BillK »

I cant really answer your question but personally I cant imagine a "ball" type hone working worth a darn in a 2 stroke with the ports in the bore.
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mag2555
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Re: Flex hone Rotax 787

Post by mag2555 »

Yup! A ball hone will not do ya.

You need a K-D tools cylinder hone for a 2” to 7” bore with 240 grit stones.
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MotionMachine
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Re: Flex hone Rotax 787

Post by MotionMachine »

Are they nikasil?
rustbucket79
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Re: Flex hone Rotax 787

Post by rustbucket79 »

You could take the jugs and pistons to your local machine shop that has the proper rigid hone, micrometer and dial bore gauge to verify that what looks good is in fact correct for clearance, and can properly hone them round and true.
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Re: Flex hone Rotax 787

Post by Tuner »

If the cylinder walls are smooth and shiny just install new rings, don't do anything to the walls.

What does the Rotax service manual suggest?
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Re: Flex hone Rotax 787

Post by Roundybout »

If it’s a jet ski seedoo type engine, they aren’t Nikasil plated from the factory. In that environment most just replace the liners +1 size for the bigger bore. And often lol.

Be careful on the ports. Some of those angles are pretty specific and important in the overall performance. A dedicated 2-stroke shop isn’t much in the scheme of things to have it done correctly.
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Re: Flex hone Rotax 787

Post by David Redszus »

If the bore is to the proper size and shape, a ball hone will work fine, using the correct abrasive.
If the size and shape are not correct, a rigid stone must be used for shape correction.

If the liner is cast iron, a silicon carbide abrasive should be used.
If the liner is Nikasil, a boron carbide or Borazon abrasive should be used.

For surface finish, either a rigid stone or ball hone may be used.

A two stroke should have the port edges de-burred, either by hand or by using ball hone.

A diamond abrasive may be used for metal removal but not for final finishing.
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