Top end rebuild questions

[bondo]

Need some advice on specs, parts, etc . . to freshen up the top end on my '08 DE300.

The bike lost all compression just before a ride yesterday (I could push the kickstarter through its stroke with my thumb!).

Pulled the top end apart and found a stuck ring (both rings seem pretty well worn). It's a good thing it lost compression, because when we pulled the piston,
we found hairline cracks on either side of the piston skirt - who knows how much longer it would have run before it ate the piston?

So, now we're looking at a new piston rings, etc . .

I have two questions: First, can anyone suggest sources for new parts.

I found a standard size piston on the Wiseco site. GoFasters offers an OEM piston (for $271.00!!). Any other sources?

Second question: Can anyone give me advice on how to judge the wear on my cylinder liner? And if the cylinder is worn, what are the best options?
Reline the cylinder? Replace? Oversize piston? . . . .?

Also, just thought of a third question: Can anyone direct me to a source for the Service Manual for this bike. Something with info like correct cylinder diameter, wear limits, etc . . ?

Thanks for any help you can offer.

 

[moto9]

Need some advice on specs, parts, etc . . to freshen up the top end on my '08 DE300.

The bike lost all compression just before a ride yesterday (I could push the kickstarter through its stroke with my thumb!).

Pulled the top end apart and found a stuck ring (both rings seem pretty well worn). It's a good thing it lost compression, because when we pulled the piston,
we found hairline cracks on either side of the piston skirt - who knows how much longer it would have run before it ate the piston?

So, now we're looking at a new piston rings, etc . .

I have two questions: First, can anyone suggest sources for new parts.

I found a standard size piston on the Wiseco site. GoFasters offers an OEM piston (for $271.00!!). Any other sources?

Second question: Can anyone give me advice on how to judge the wear on my cylinder liner? And if the cylinder is worn, what are the best options?
Reline the cylinder? Replace? Oversize piston? . . . .?

Also, just thought of a third question: Can anyone direct me to a source for the Service Manual for this bike. Something with info like correct cylinder diameter, wear limits, etc . . ?

Thanks for any help you can offer.

Most important thing you want to thoroughly check out is the condition of the cylinder, you could send it out and get it re-plated.
Check the back of the cylinder and see if it's a "A, B or C" ...I have the same bike and I Used a C piston in a B cylinder, just to get a little tighter fit.

You can get a Manual off this site...not sure about spec info...and parts sources are Gofasters, Ebay and specialty companies like Weisco, Millennium technologies.

 

[bondo]

Thanks for the input. I've looked around the site for a service manual.
Found pdf versions of the owner's manual and the part manual on the GG factory site, but so far, no service manual.

Not familiar with Millenium as a source for pistons, etc. .
I've also read some threads indicating that Vertex may offer a top-end kit for GG. Any knowledge of that? Anyone have a good source for cylinder re-plating?

 

[twowheels]

Thanks for the input. I've looked around the site for a service manual.
Found pdf versions of the owner's manual and the part manual on the GG factory site, but so far, no service manual.

Not familiar with Millenium as a source for pistons, etc. .
I've also read some threads indicating that Vertex may offer a top-end kit for GG. Any knowledge of that? Anyone have a good source for cylinder re-plating?

Wossner makes a piston kit (in three sizes) for $160. Millenium is about the best there is for replating. Given the piston specs they can set up your cylinder with a fresh new bore that matches. I use both of these companies with confidence.

 

[bondo]

Thanks for the reply, tw.

Found the Wossner site online. U.S. dealers?

Also looked at Millennium's site. They seem pretty reasonable on replating or trade-ins.

I would still like to find out what the piston to cylinder wall clearance is supposed to be for the 300. I measured wiht a feeler gauge and the clearance on my cylinder / piston is .007".

 

[wence]

ec_shopmanual_06.pdf
This was what I downloaded and has the tolerances etc inside.
Not sure where I got it from though.
This is amount of piston play from the manual,

Play of the piston at 200 cc: STD: 0.05 mm
assembly Limit: 0.10 mm
250 cc: STD: 0.055 mm
Limit: 0.10 mm
300 cc: STD: 0.06 mm
Limit: 0.10 mm

Ring gap,

Opening at the end of 200 cc: STD: 0.3 mm
the ring Limit: 0.6 mm
250 cc: STD: 0.4 mm
Limit: 0.7 mm
300 cc: STD: 0.5 mm
Limit: 0.8 mm

Cylinder diameter 200 cc: STD: 62.50 mm
Limit: 62.60 mm
250 cc: STD: 66.38 mm
Limit: 66.50 mm
300 cc: STD: 71.99 mm
Limit: 72.10 mm

Hope this helps,
Cheers Mark

 

[GMP]

Unless you have access to some proper measuring tools, the numbers won't be worth anything. You also need to measure it in the right place and check bore concentricity. Have a shop measure it for you. Non-OEM packaged pistons like Vertex are usually supplied with recommended clearances.

For the plating, if there is no damage like scoring or chips, and if you can see the original cross hatch honing marks even if they are glazed over, you will be fine. Deglaze the bore and go up one micro size, from A to B for example.

 

[widebear]

What Glen said! Also bear in mind that a new piston may not be of the advertised size,I've seen a brand new out of spec factory KTM 200 piston. I've got my regular machinist who I allways use. For a dozen Tim Horton donuts for his crew I can get my cylinder and new piston measured.

 

[bondo]

Wence, GMP, Widebear,

Thanks for the all the info.! That's just the sort of helpful stuff I need to make an intelligent (and economically sound) decision about freshening up the top end on this bike

 

[bondo]

Top end rebuild questions: part 2

Just an update on this thread. We did have Millennium Technologies re-surface the cylinder. Found a Wiseco piston kit at the distributor and sent the piston with the jug so Millennium could match the two.

Now we are rebuilding the bike and this is my first rebuild of a GG power valve assembly.

The shop manual is extraordinarily unclear about the assembly procedure as far as what position the two exhaust valves should be in for assembly. I'm aware that the exhaust flapper valve will be in it's lowest position, but will the right and left exhaust valves necessarily end up in
their proper orientation to the transfer ports? When we took the engine apart, things were too gummed up with carbon to get a good look at how the two exhaust valves should be oriented.

 

[gasgasman]

In my experience, the sticking rings can be caused by ethanol blended fuel.

 

[bondo]

I did not know that. Either way, the engine definitely needed a rebuild.

Any help with my question about the power valve re-assembly?

 

[ggalex]

[edited 2/7: I was mistaken about the lack of an index on the right side power valve shaft to position the mounting of the lever, there's only one way, at least on the 06 I just bolted back together. Basically you can't get the rotational orientation wrong. Just go in reverse of the dissambly advice linked below and use a little locktite blue on the retainer screws.]
See
http://www.gasgasrider.org/pv_disassembly_mattr.pdf which at least has dissassembly process, but indeed it does not state how to orrient the side power valves on re-assembly. (PDF covers 200-300, not 125 which is different design.)

BTW, I used PowerSeal in PA and they measured it all up and were able to do a light hone ($45), did not need replate tho they say GG cyls come kinda thin on the factory coating (it just takes 300s forever to wear out), thus saving me a good buck. The piston kit they matched up to the honed cyl was a Wiseco at $185. Only needed to get the pin brg from GG dealer. Happy with this outcome.

PS: I have a wicked big squish gap, 0.10-0.14" so I'll be going to RBD...