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Hey guys, I'm looking to do a top end refresh on my 06 660. I have about 5500 miles and would like to do valve seals and stay at stock bore, new piston and rings. passing down to my son and I'm moving up to a 700. Any recommendations on who I can send my cylinder and top end to for machining ? I used to use a trinity racing back in the 2 stroke days. Thanks in advance

Pat
 

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I would think for no more than you're wanting done a local machine shop could take care of it very easily. The only way you'll be able to stay at stock bore is if your jug is within specs and just go with a hone, unless you plan to buy a stock bore jug. I wouldn't be afraid of doing a slight over bore though.
 

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Agree you could get a new jug or just try and clean the old jug. If it was me I would get a new one, you get what you pay for. I would want all new parts then no worries.
 

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So after having 3 Grizzlys I know when to use Yamaha parts and when I can get away with others. Maybe just a hone if possible, any ideas on a new jug, OEM or is there a better aftermarket company out there ? Thanks.
 

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So after having 3 Grizzlys I know when to use Yamaha parts and when I can get away with others. Maybe just a hone if possible, any ideas on a new jug, OEM or is there a better aftermarket company out there ? Thanks.
You can do what you want but a new jug is around $350 plus your piston kit which is roughly $120 from Yamaha. Normally you can get your jug bored for less than $100 and sometimes less than $50. You're looking at saving around $250-300 by boring your jug vs buying a new standard bore jug. I wouldn't be afraid in the least to do a .50 over bore or something similar. There are plenty of companies that make quality pistons but if you're set on OEM, even Yamaha offers over sized pistons .50 and 1.mm over for the 660.
 

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Before doing all this work, I ask the question of why? Is it burning oil? Is it down on compression? Have you done a compression test?
If you are not having any issues, then why do all this work to a perfectly working engine?

If you need to do the work (or you just want to), then before ordering any parts you should first do a compression test to get a idea of the condition of the engine. Then you should remove the cylinder and inspect everything. You may need to do a overbore and install an over-sized piston. If you have cylinder wall damage, you'll need to measure it to see how deep an overbore you'll need remove it. OEM Yamaha over-size pistons for the 660 only go up to 1.0mm. Aftermarket pistons go up to 2.0mm. If the depth of damage is over 2.0mm, then you will need a new cylinder.

If your cylinder is in good shape and does not require re-boring, then just replace the piston and rings and ride out. Contrary to popular belief and old habits of the "norm", there is no need to hone a good cylinder. New research in the last 10 years or so has proven re-honing a perfectly good used cylinder actually slows the break in of the new rings and can actually hurt performance. This is totally against everything I knew about rebuilding engines, but it has been proven time and again, even by race teams from multiple facets of different types of racing from around the world, including the automotive sector.

The most surprising part of this to me was the cost of OEM Yamaha engine parts. They are actually very competitively priced. Actually when I did my piston/rings/valve seals 3 years ago, it was about $100 cheaper to do it all with OEM parts than it was with aftermarket (JE Piston/Wiseco).
 
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