Honing 1974 Yamaha RD200

[duraacemike]

Where a good place to go to get my cylinders honed in Auckland and do I need the new pistons before I can send them off to an engineering shop to get it done. Some sites say you need to be able to measure the new pistons before you can hone the cylinder. is that right?

[blackdog]

I don't suppose buying a hone and micrometer had occured to you?

[Woodman]

Where a good place to go to get my cylinders honed in Auckland and do I need the new pistons before I can send them off to an engineering shop to get it done. Some sites say you need to be able to measure the new pistons before you can hone the cylinder. is that right?

What oversize are the new pistons? What happens if the wrong ones arrive and the honing has already been done?

A lot of aftermarket pistons have specific boring instructions, but ususally standard plus oversize.

I would wait till they arrived.

[Madness]

What's the bore size roughly?

[blackdog]

What's the bore size roughly?

Roughly the diameter of the hole the piston goes in.

[Madness]

There's a couple of brand new Flex-Hones (http://www.brushresearch.com/flex-hone.php?gclid=CKSQ_oaZmK8CFVGApAod_RQKzw) sitting at work looking lonely.

[blackdog]

There's a couple of brand new Flex-Hones (http://www.brushresearch.com/flex-hone.php?gclid=CKSQ_oaZmK8CFVGApAod_RQKzw) sitting at work looking lonely.

Dare I ask how much? I used mine for my first engine in 1988.

[duraacemike]

yeh i figure I need a micrometer to first measure the bore and establish whether i need 1st overbore as it is a bit oval. Then i can talk to the piston manufacturers, get their dimensions and figure out if i'm honing or 1st or 2nd overbore.

[Madness]

Dare I ask how much? I used mine for my first engine in 1988.

I'll ask. I'm the new boy that knows nuffink.

[blackdog]

I'll ask. I'm the new boy that knows nuffink.

You'll be the ol' boy that knows nuffink soon enough.

[Woodman]

How much oversize are you going to. 010",020" ?? Why i ask is that it will take ages to even hone out .010" and i can guarantee that the bore will not be straight when you have finished. It will be "barrelled" e.g. bigger in the middle.

If you do insist on honing it do not use a flex hone, rather use a fixed hone, but my advice unless its a .002" ish oversize is to get it bored and honed.

[Ocean1]

get it bored and honed.

:yes: Firstly, one doesn't hone a cylinder to size, you bore it on a mill, (or lathe). Honing is simply to make the finished bore the correct texture, so the rings and piston skirt bed in nicely.

Secondly, if you put a ball hone anywhere near a two stroke you'll fuck both the hone and the cylinder.

Much as I'm a fan of DIY this is one you need to pay someone with the right gear to do.

[duraacemike]

Here goes;

Bore supposed to be 52mm

But currently measures as

LHS 51.92mm across and 51.82 front to back

RHS 51.89 across and 51.80 front to back

Out of round tolerance is 0.01mm but my cylinders are (51.92-51.82) 0.1mm so well outside tolerance range.

But normally the standard piston is 51.96, so with honing I should be able to get them round again and still fit the standard pistons?

Does this sound reasonable?

[Woodman]

How is the bore smaller than standard?

[duraacemike]

F#%&ed if i know, That has me puzzled.

could be that I am measuring with verniers at the top of the cylinder not a proper micrometer?

But it sound like I need to get the cylinders bored 1st, then honed, so once I've got proper measurements then i can figure out which, if any overbore I need.

[Ocean1]

Does this sound reasonable?

No. Sounds like you're measuring the bore above the point the ring sweeps, it'll usually be completely unworn there.

A proper bore survey measures X and Y axis at the piston mid-skirt position BDC, Mid-stroke and TDC. No one of those should exceed the overall bore tolerance and no two should exceed the out-of-round or taper tolerances. Nore should the lip at the top be more than, say 0.05mm. You need either telescopic guages or an internal micrometer to measure it correctly.

If the bore survey does find it's oval by 0.1 then you need to bore it, and that means buying first oversize pistons, (if they're currently std). Do that first, give the lot to the shop with any factory tolerances or other data you have.

[Woodman]

You cannot measure bore wear even close to accurate with verniers.
A 2 stroke will have most of its wear in the middle of the bore where the ports are, making them reasonably difficult to measure accurately to see which oversize it will clean up at. The reason a 2 stroke bore is awkward to measure is that quite often it is hard to get a ball gauge or similar at a 180 degree axis because of the ports.