KTM Top end question

Strick

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#1
Fellow pumpkin riders/rebuilders;

Base Gasket Thickness. Do I have to remove the cylinder and measure, and order the correction combination of base gasket(s), or is there base gasket 'kit' you buy, and choose the right combo from the options given?

For those of you who read this board and the other (KTM) board, please excuse my redundancy.


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Strick '99 KTM 300mxc, AMA & BRC member

[This message has been edited by Strick (edited 02-25-2001).]
 
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#2
I bought Cometic and it came with 2 base gaskets.

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"Nature Boy"
 
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#3
HELLO FELLOW KTM FANS!!
YES,,, You should measure the thickness of the base gaskets you removed. This will give you a starting place in selecting the right thickness of gaskets. Hopefully you have a good dealer to work with and can get extra gaskets, and just return the ones you don't use. Get several sizes, and ALWAYS MEASURE the Dimension X (deck height) Set to KTM specs according to the manual. Some models require a special tool for measuring this, so you might want to check with your dealer reguarding this procedure. Don't rely on the measurements of the new gaskets for calculating the distance, as the new gaskets will crush when you torque the cylinder down.
GOOD LUCK! TEAM ORANGE CRUSH!!
 
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#4
Strick,

Measuring the old gasket is not the best way, as its compressed slightly during installation. I rebuilt several 300 EXCs, just finnishing one last week, and this is how I do it:
First get a good metric caliper. Clean old gasket material from all surfaces. Put the new (or cleaned original) piston on the rod without rings(is eaiser for this temp installation). Put the cylinder on the cases without a gasket and hand tighten a couple of the base nuts. Move the crank with the flywheel to TDC. Carefully measure the distance from the edge of the piston dome to the cylinder deck. This is the required base gasket thickness for dimmension X = 0. You should round off to the next thickest available size as it won't be exact, and X must be between 0 and .1mm.

After your power valve is cleand and reassembled (locktite on all fasteners) set the main flap height to 46mm from the cylinder deck to the center of the flap edge when the valve is fully closed. This is dimmension "Z". If everything is done correctly, the PV control rod will snap on the ball joint without any vertical preload after the cylinder is torqued down. Good Luck.

Glenn
'00 GasGas XC250
 

LoriKTM

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#5
Hey Strick,

When my husband did the top end on his bike (1999 250MXC)last year, he was able to order a top-end gasket kit from the dealer (don't remember the cost). It had a bunch of different thickness base gaskets in it. I believe the kit # is listed in the parts manual, I think it's the same kit for 250's and up.
 

Strick

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#6
What does everyone think of Wiseco? I hope your input is positive. It's already paid for and on order.

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Strick '99 KTM 300mxc, AMA & BRC member
 
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#7
Wiesco made a batch of pistons for the 300 that the front piston skirt was to wide so check it with your stock piston to make sure you got the right one.If you got one like I did & the piston skirt is wider than the stock one you will no upon start up when the skirt makes contact with the crank webs(sounded like a very bad lower rod bearing)

Steve F.98 300EXC
 

MikeS

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#8
Hey Strick

You will probably get mixed opinions on pistons. Personally I found the stock KTM pistons to be very long lasting. Maybe 2:1 with equivlant ring changes in My applications. But for atleast a 2:1 price difference for Wiseco you get 2 fresh pistons instead of one.

Also I think Wiseco may offer 2 ring versions for some bikes. That some prefer.

The Wiseco is usually lighter and allows quicker reving. Most are also forged and require a little more care on warm than OEM cast pistons.

As for oil and break in I used the same oil as a run normally. You can always Contact the Oil Manufacture for their official recommendation.

Mike S
 

Strick

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#9
Mike S. - Thanks! I am going to replace the top end every year. My compression read 160 this weekend, and I have ran the bike a full season + one race. I think it's time. I look at it like that old oil filter commercial: 'You can pay me now, or you can pay me later.'

A riding buddy of mine waited too long recently, and had to have the cylinder resleeved, because of the damage.

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Strick '99 KTM 300mxc, AMA & BRC member
 
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#10
STRICK,

I have to agree with MikeS, that you will get mixed opinions about the pistons, but the stock KTM pistons are forged units also, comparable to the Wiseco's. The KTM pistons are definatly more expensive, but seem to last much longer than the Wisecos, without the worry of fitting right!!

The most important part of any engine is a good Air Filter, with a tight intake tract, that is maintained well!!

Motowrench
 
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#11
There are several other threads on this subject. I think proper fit has a lot to do with it. An OEM Wiseco GasGas piston will last as long as an OEM KTM piston, but there are 4 mico sizes to achieve a precision fit, and only 1 replacement size for a KTM.

Glenn
'00 GasGas XC250
 

Strick

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#12
Motowrench, et.al.:

I am a maintenance freak!! Anyone who knows me on this board or elsewhere can attest to that. One ride per air filter summer & fall, two rides max during winter & spring (I have 6 air filters). Gearbox oil changed every other ride, or every race (Mobil 1 15w-50 synthetic). Gas is never kept for more than a couple of weeks, and I use 50/50 race gas at 40:1 MX2t.

I will mic the Wiseco piston as soon as I get it as well as the cylinder. I will also check tolerances with the piston inside.

My question to all commentors is this. Why is Wiseco O.K. for all the other bikes out there but not KTM? I can't imagine the piston being an inferior product. KTMs are not the typical type of rebuild. With Z & X dimensions to be considered, there seems to be more to it than other 2-strokes.

The biggest reason I ordered Wiseco is, I don't feel I get straight answers at my local KTM shop. Can you imagine a parts guy telling you that at 2000 miles, and 160psi compression (~200 new), that I should just wait to put a new top end. He said until the compression drops to 125, or I feel a power loss should I consider a new top end. HELLO! I think he was looking for a little replating job. Or maybe a total meltdown including bottom end. <Keep in mind this is the same guy that sold me a Delta I, as a Delta II reed assembly.> I already had the bike partially disassembled anyway to put in a Delta 2 reed cage, and do some deeper inspection after my last race, so now is the time!

I envy you guys that are treated fairly (and Honestly) by your local KTM dealers. The only other reason Wiseco is attrative is ease of getting the parts quickly.


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Strick '99 KTM 300mxc, AMA & BRC member
 

TexKDX

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#14
Strick, pull the jug and replace them with the quantity and color that came out. The thicknesses are color-coded. Green and white. The dealer sent me two whites and a green, mine had one white and a green. That is what I put back in. Next time I'll just order a green.
 

MikeS

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#15
Strick

I don't have hard scientific data to determine which is superior. The KTM , I think is a Mahle and is very high quality, it has a coating that helps prevent scuffing,plus it seems to be thicker/denser.

Some say Wiseco loses it dimensions faster. Being lighter suggests that material was left out somewhere. I never let that happen any way by changing the piston after every other ring change or when it goes out of spec. If you are a low maintance person then the OEM KTM is a better choice IMO.

Dealers are sometimes tough when it comes to suggestions. I have alot of dealers within a hour or so travel and sometimes I consult all to get the best Average answer. A couple of them race everyweek and service their own stuff so they usually have valid info.

Hope you get it together soon , it is a shame to leave that pumkin just sit around....

Mike S