250-500cc wr 360 decomp head my way.

right ive been running this decomp head i fabricated for a few months now and realised i hadnt posted any info on how to do it yourself with a little help.

my bike is a wr 360 2002


so first off i got my head off the bike and got my trusty mate with cnc mill to bore a hole completly through, the outter is 25mm and the inner to combustion is 14mm, in hind sight i would bust 25 through the both,


i then got a slug of high grade ally from the local foundry, this was free, i machined it up on a clapped out bridgeport


i then took this to litewelding in nailsworth to a bloke called hotrod pete he does ally welding and hooked a bruv up for a tenner



then i took it back down to the hobbits downstaires (the bloke an his cnc mill)
he drilled the final hole to accept the chainsaw decomp valve he resessed it into the slug to,


then a bit of finnishing install the valve and ta da




the thing i would do now given the option would to have stuck the 25mm hole right through, then put a 14mm resessed spark plug thread so i could get an auto decomp in there. as it stands im 99% chuffed, i simply press the valve in an kick back not down she starts no more hanging aroung on the jabber waiting for tdc.

Great info! Feel like doing another one Juicy?

Can you start it in your tennies

How good is it when home (hack) jobs work so well. Yeah as Mr Noob said what about the weld in the combustion chamber? That would certainly affect the combustion wave, power output, wear on internal bits etc. Maybe not much but I'd be a little concerned, given its nearly 3 years old can you say how it has held up?

Yeah send me a head an I will sort it out.
Not sure how you guys managed to dig up a 3 year old thread tho.
It's been working well yes I can start in tennis shoes but as it's chainsaw decompression valve it has to be reset and the second stroke of piston on up stroke shuts the valve.
Most of the issues stemmed from my carb.
I'm now running less squish than manual states but it's still very safe, could take more off.

I did file the weld smoother but really it's not noticeable and the piston crown is evenly carboned over.

I have a 92 WXC 360 I have been wanting to do this kind of mod on as well. I sourced the Victa decompression valve from down under and just need the the head modded to accommodate it. May be in Ipswich visiting family this fall so could post it from there to save some coin if you are still fiddling with these. Let me know what you charge to do the modification. Cheers

I have the first one back

Yes I have a head wich isn't used but it's the m10 thread, think auto valves are available in that size but a bit hard to find.
Up to you what you want to do, straight swap or put size valve in you like.

Awesome, let us know how it performs.

What did it set you back in the end?

it was 125 for the mod

if anyone is interested in this mod PM me for the details

Here is the kx500 version, very clean

http://oem-cycle.com/forum/viewtopic.php?t=184

thats nice
what I am trying to do involves an auto decompressor
no reaching down its automatic

Hello, where can I have my head sent for this mod? Cheers

Well either 2premo in USA
Or
Me in UK sup to you I'm not fussy, premo's is cheaper than my guys as it would cost about that in £

i agree, we do this for fun
if anyone wants it done through my guy i get nothing from it but satisfaction of helping

PM me for address
if you send yours it is five at once and he offered a discount on five
will find out what that difference is and get back to you

by the way the actual decompressor is from your area
could you find out the cost of buying them there

The decompressors are from a Victa 160cc lawnmower.

Up until the 1980s Victa used the long compressor pictured in the post above (aftermarket)which is getting hard to find.

The short decompressors are readily avialable. The boss welded into the head will need to be longer though otherwise it may hit the plug.

The trick is to get the decompressor which can be dismantled (newer Victas have a sealed version) so you can adjust the spring tension which holds the valve open to suit the compression of the engine.

https://www.allmowerspares.com.au/victa-decompressor-assembly-short-valve-en72541a-en72541p.html