Compression release hole?

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Oct 17, 1999
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#1
I have looked all over for the correct location of the low speed compression release hole in the cylinder of my 98 KTM 380. I just had to tear the entire bike down to repair the kickstarter mechanism for the umpteenth time. While it's apart I'd like to add the compression release hole that the '99 and up 380s have, as they don't seem to have any kicking troubles, and they run happier at extreme low rpms. So far I have heard that the hole is 2mm or around .080in in diameter. Does anyone know if this is correct, anyone know the position? I figured maybe Gorr would know since he has probably seen some of the cylinders apart. Otherwise, perhaps a grizzled vet can shed some light here, as I'm sure the other older openbikes have needed this at some point. Thanks for any help or advice.
 

jeb

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#2
The only advice I can give you is that I know Holeshot KTM was doing that retro-fit. I had a 98 380 so I followed those threads when they came out but I don't remember anyone giving exact deminsions, angle or position of the hole. Good luck.
 
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#3
Holeshot wont tell me where it is or how large. They offered to perform the retro fit, but I'd have to mail it both ways and wait, plus paying for something I can have done for free with no waiting. I know holeshot markets their experience, something which sets them apart from other shops. But it kind of irks me that they can't even give me the location of the hole. It would be different if this was a service that holsehot had created through testing or something, but KTM has added this hole to all the new cylinders. Anyone know any KTM factory tech numbers? Someone somewhere has to know.
 
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#5
Talked to the place I'd bought the bike from and it sounds like KTM isn't telling people either....hmmm Well anyways, they said that it would be around 40$ which is around 60$ less than holeshot, and probably the shipping is going to save me another 30 bucks :) Still seems like KTM should foot the bill to change it, since it has caused me to replace the kickstarter spring about 4 times in a year, and then the roller bearing on the kicker went out this time. I have purposely baby-kicked this thing everytime since the first time the spring broke. But I guess it's a MX bike.
 
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#6
Roadrunner - since I last posted you I had reason to removed my '98 380 cylinder. Measured the (depth) location of the hole. The top of the decompression hole is 1 and 20/32 inchs down from the cylinder's head surface area. From a visual perspective it appears dead center located to the front of the cylinder. When the power valve is removed you can see where the hole terminates on the exhaust side. I DID NOT think to place a drill bit into the hole in an attempt to determine if the hole was angled. I do not believe it is.

The hole could easily be drilled from the outside of the cylinder inward once the power valve has been removed. There is no liquid cooling passages in the immediate area of the hole and no intergal support ribs for the cylinder. Your stock piston rings are pinned in a different area and therefore I would quess you could go from there.

Concerns: 1. My primary concern if I were going to install the hole would be the inner plating on the surface of the cylinder. What speed and cutting fluid should I use to minimize the chances of flaking some plating from the cylinder's surface. 2. Can I deburr the hole on the piston's side without compromising the plating?

My cylinder's modification was done by H&H and ran about 3000 miles without a hitch.

BTW - if the spring you are breaking is the small pawl spring; the hole will not have any effect one way or the other. I replace mine yearly and it always appears it- is- just- in- time. (Yes I have chamfered the top of the spring retaining hole and it helps but does not eliminate the binding problem)

Eric should have my cylinder this friday for his 1mm performance package upgrade. Maybe he will share additional information with you. Unless your "free shop work" involves an experienced person: it may end up costing you many times the 50 to 100 dollars you saved.

Best-of-luck to you!!
 
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#7
Compression hole

You can take your cylinder (w/o any of the powervalve installed) to your local KTM dealer. They can send it to KTM Ohio, to have it drilled free of charge. You are only charged for the shipping to and from and it is drilled at KTM using a special "jig".:)
 
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#8
KTM drills the hole for free? Dang that sounds about right. The fact that my kickstarter spring is perpetually broken is kinda depressing, hoped that the chamfer would fix it, but I imagine that the reduced compression and the chamfer together will help quite a bit.