Top end rebuild

[aah5]

I have a Skorpion Tour that is getting quite a few k's on it (110,000) and is just now starting to show signs of oil consumption,no nasty noises from the engine still as quiet as the day of purchase. Has anyone done a top end rebuild,piston,valves and guides etc.,who can recommend whether to use new Yamaha parts or go for aftermarket valves,piston and so forth. What has been your experience?

[DAVID THOMPSON]

i use bikes as daily drivers if mine i would go with a very good rod and bearings the rest stock yamaha parts
except the piston rings german made

dave

[Bill Jurgenson]

as long as you are satisfied with performance, stay with Yanaha parts.
Use the OEM valves and guides regardless of tuning stage. They are hard
to beat and there is no reason for larger valves. The titanium exhaust valves from the Raptor
would fit if you really think you have to splurge.
Use new valve shaft seals. That might even be sufficient. It will depend on how much the guides and valveshafts are worn.

Don't tamper with the conrod unless you absolutely have to. So, don't break the crankcase unless you need to The OEM rod is good enuf for 80tkm with 60hp.
A carillo rod is very fine - but it is also heavier and requires reblancing and is not necessary unless you
are into heavy tuning and over 60hp. If the small end is shot, have a bronze bushing inserted. Or use
a new OEM rod. Either way, the crank has to be pressed apart.
Chances are you will not need to. If you do have to break the crankcase, replace the bearings even if they seem to be OK.
whatever else use a new timing chain!


You will need a new piston; oversized OEM or Wiseco 101mm.

[aah5]

Have just been pricing parts for the rebuild. Locally sourced parts for XTZ660 from my Yamaha dealer will cost Aus$1492.00. This is a bit too expensive in my opinion,but did a search around the web and found PowerPartsPlus in Texas.Their price for equivalent Raptor660 parts US$415.00 (Aus$620.00 + shipping), certainly a lot cheaper, What is the cost of parts like in your part of the world, they are certainly sticking it to us in OZ, and they wonder why we look offshore for our parts.

[samandkimberly]

Have just been pricing parts for the rebuild. Locally sourced parts for XTZ660 from my Yamaha dealer will cost Aus$1492.00. This is a bit too expensive in my opinion,but did a search around the web and found PowerPartsPlus in Texas.Their price for equivalent Raptor660 parts US$415.00 (Aus$620.00 + shipping), certainly a lot cheaper, What is the cost of parts like in your part of the world, they are certainly sticking it to us in OZ, and they wonder why we look offshore for our parts.

Take it apart first, see what's worn, then replace only those parts that are worn. You might be surprised at what -doesn't- need replacing.

Sam

[aah5]

I always like to have all the parts on hand so that the work can be compleled as quick as possible. it has begun to look like a 2srtroke when it is started in the mornings,suspect valvestem seals and guides are worn,doesn't appear to be any blowby on piston,but has started to use oil fairly quickly. I reckon if you have gone to the trouble of pulling the head and barrell off you may as well replace all the parts that are subject to wear,save having to do it to later.

[samandkimberly]

I always like to have all the parts on hand so that the work can be completed as quick as possible. it has begun to look like a 2srtroke when it is started in the mornings,suspect valvestem seals and guides are worn,doesn't appear to be any blowby on piston,but has started to use oil fairly quickly. I reckon if you have gone to the trouble of pulling the head and barrell off you may as well replace all the parts that are subject to wear,save having to do it to later.

Valves/guides can last 100s of thousands of miles in general - would you pull the head on your car and replace all the valves/guides at 100,000 KM? If your motor has been well maintained then you very well might find that all the intakes are like new; possibly the exhausts, and perhaps a single guide might need replacing. Leaving the parts that are working and not worn out in there makes sense from a finance perspective but also from a mechanical one: any time you install a new part that involves a press fit like a valve guide you introduce a small amount of risk - the old one may be galled and not come out perfectly; the new one might go in too tight, or too loose, or not straight. As far as the valves: sure, replace them if they show any wear at all. But your intakes in particular quite possibly will be perfect.

When checking the parts, keep in mind that if they're worn but well within running clearance than you are probably not helping anything by replacing them. Mechanical parts do not wear evenly over their life - generally they can wear significantly when new as they bed in/establish working clearances/compensate for misalignment. Then, they wear very little for a long, long time. Spend your money on a real good valve job, replace any valves that are worn but don't go changing guides if you don't have to. Ditto for the piston if you're not hopping it up and it's in spec; just buy rings.

BTW - take special note of Bill Jurgensons comment - Yamaha uses very good parts. Replacing barely worn stock stuff with new aftermarket stuff could be a step backwards.

One last thing - before you tear it down, get all the evidence you can as to what you're looking for when you take it apart. If you can, do a leak down test. Check carefully around your crankcase breather hose - is it blowing a lot of oil into the airbox? Do a compression test, dribble some oil into the spark plug hole and do another. If there's no difference between the two and there isn't a lot of oil coming out of the breather don't even touch the piston/rings. That would surprise me though, singles do go through pistons. But you may be rebuilding a motor that only needs valve guide seals.

Sam