Topend rebuild. Bore measuring.



  • I would like to do a topend rebuild as the previous owner never did one so is probably over due for a rebuild.
    I would like to measure the cylinder bore and was wondering if a digital vernier calliper would be able to do this task accurately. Any help would be grand!



  • I was always under the impression that the tolerances are too small to measure with verniers and were in fact done with lasers, especially when out of round bore tolerances were considered. The difference between needing a hone and a rebore.

    Either way, the piston crown will tell you whether it's been rebored. I would always recommend having the bore honed when doing a new install. At which case you might as well let the company do the measuring.

    If you're doing it on a budget (been there). Just giving the bore a visual inspection and examining the piston crown would suffice. Ensuring no scores or nasty marks on the bore.

    I've done that too and to great effect.



  • @calum yeah plus 1 on the measuring I let the shop do mine so I get the right piston gaskets and they even measure ring gap for free so there’s no mistakes



  • @declan Doing the ring gap I'd do myself. It's very easy and satisfying job to do. It's a really good thing to be able to do. So is honing, but I feel the cost to have the appropriate honing equipment is too great. A diamond file costs literally pennies.



  • @calum I’ve never done endgap and don’t know if i will the way I see it they should be up to spec as is. But obviously as you have stated they sometimes aren’t why do the wossner pistons need it doing so much you’d think paying double the price of a mistake that all that would be on spec



  • @declan Definitely not on Wossner pistons, always one is out of spec and this is by design.

    If you're buying high end components, it's assumed that you're running greater than stock power. It is then an assumption that your barrel is modified. As a result you may have tighter tolerances.

    If it's a mitaka piston then fair enough. But the moment you start buying forged components, you can be sure that they make no assumptions. Rather a little too much than too less.



  • @calum ahh that’s pretty cool I guess I can’t find anything on the internet does skimming the head increasing compression give any power or performance benefit or is it just to get rid of warping I can’t find anything that says it increased performance



  • A general rule of thumb, the higher the compression the greater the power. On a two stroke, a great deal of power is made in the head.

    But it's not a case of skimming the head, you need to modify skishband.

    Read Graham Bells Two Stroke Performance Tuning for infinitely more detail.


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