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Xr600 auto decompress?

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I've been trying to do my research! But haven't really found anyone in my boat, so I started with an xl600 engine, which has the auto decompress that goes to the center of the head with that 5th little valve, but now that I've switched to a whole xr head I don't have that guy and I feel like I'm going to break my leg kicking through the compression stroke, already tore my pants... :( so I hope this doesn't get me into trouble but I'm using an xr650l cam because it was a good deal and came with those end bearings I needed, its got that funny round thing right before the gear on the cam, and that fat rocker arm.. that's as much as I know, I know its suppose to have some kind of clutch system.. but ya.. looking at a parts explosion doesn't do much without an explanation either, I don't understand how it works, and I currently don't have the manual decompressor yet so, well I just want to keep myself off crutches.. so far the only firing the engine has done has been back at me, launching the kickstart at my leg, which doesnt quite tickle

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You will need to be more specific on the model year of the head you are using and the year and model of the XL600R, in the rare case it is something other than a U.S. model, other than that it shouldn't matter.

 

Without knowing more about the head you are using (which I'll guess is the dual carb XR600R head), the XR650L cam is not compatible with the head. The lobe spacing is different.

 

The XR600R didn't get an auto decomp on the cam until 1988. If you are using a cylinder head prior to that, it also doesn't have parts 8 & 9 from this diagram http://www.bikebandit.com/houseofmotorcycles/1988-honda-bike-parts/o/m3102sch93033.

 

Without that pin and spring the auto decomp won't work. The exhaust rocker arm is also different, depending on the year.

The auto decomp is also and anti-kickback device and the functions are separate, but won't work without that pin and the correct rocker arm.

 

The cam chain and sprockets are also different unless you somehow got the XL600R cam sprocket onto the XR650L camshaft. The XL600R has, or it once did, a manual decomp which works just as well as the auto. The XR600R head you are using, no matter the year, should  have a manual decomp provision on it.

Edited by Onederer

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Dang , kick through the comp stroke?ouch ! crank slowly till it comes up on compression,pull on comp release levercrank it a few degrees past tdc and kick it. Starting big xrs is an art , you can make it easy or hard.

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It's hard to tell in the pic, but is #8 and #9 a little pin with a spring coming out the bottom, because I have two of those but had no idea what they were for, they came with my head not the cam.. I can't remember what year the cam is, its 90's though, the head is 1992, and I switched to a single carb, it does have the manual decompress

And I also switched to a post 88 cam chain and bottom sprocket with proper chain guides

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Get the parts to hook up the manual compression release and call it done.

 

What bike did you start out with? An XL600? Was the manual compression hardware there to begin with?

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Do as HeadTrauma suggests install manual release lever, cable, and cover arm. I would think the valve cover already has the activating arm or there'd be an open hole you needed to plug for oil leak. Use the proper kick starting technic, kick slowly thru to compression stroke, pull release lever kick a few more degrees, allow kick lever to return to start position (top) and kick thru full stroke. Repeat process until started. I have high compression motors and it works for me.

 

"HJ"     :cheers:

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It's hard to tell in the pic, but is #8 and #9 a little pin with a spring coming out the bottom, because I have two of those but had no idea what they were for, they came with my head not the cam.. I can't remember what year the cam is, its 90's though, the head is 1992, and I switched to a single carb, it does have the manual decompress

And I also switched to a post 88 cam chain and bottom sprocket with proper chain guides

 

It seems like you have done most of it right.

 

Did you use the 8mm head bolts for the XL or modify it and use the later 9mm head bolts?

 

The pin and spring belong in a recess in the head, below the cam.

 

If the engine won't start and is kicking back, after you have checked all the external possible problems, you should make double sure the valve timing is correct. You'll have to remove the rocker cover anyway to place that pin in. Without that pin, the decomp mechanism is just going to spin around and likely cause problems.

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K ill be popping him back off then, I really hope the timings right, it should be, but I had to do it the ghetto way because I can't get those screws off on the side of the case, is there a trick to get those off? I just stuck a flat head through the spark plug hole and went back and forth until I was sure it was tdc.. I have a wiseco high comp piston, if I was off even by a tooth wouldn't they hit? Cuz I still have compression.

So for the auto decompress, I just need the one pin with the spring, there was no reason for the guy to give me two? And I just drop him in the head with the spring down I assume? Dang, and that means I have to remove the cam again if he goes under the cam right?

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What screws are you talking about..Do you mean the stator cover inspection cover for the timing and the other large one where your socket goes. ?? Use an impact driver on them,,don't smash the hell out of it..those covers are a bit weak. If that doesn't work get a hammer and flat head punch onto them and try shifting them that way. You really want to be eyeballing the T mark in there to do the timing and rocker gaps..guesswork on it is a bit of a haphazard way to do things..

 

T on mark,,Cam lobes down..Top camchain sprocket marks level with the top of the head,,Piston top of bore..Adjust rocker gaps..

 

Yeah I think spring in hole first..Maybe he had two, who knows..Can't recall whether the cam needs to be out to get the parts in. 

 

Personally I'd have removed the entire mechanism from the cam and just used the manual hand operated decomp to start it. You're not going to know if the actual cam mechanism is good till you stick it back together and try to start it..If it won't start you're back at wondering whether the mechanism is working as it should..That's why I got rid of mine. I eliminated the possibility of it causing starting issues..

Edited by Horri

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K so I have my engine, back out.. again... The valve cover off, had to remove the cam to get to that hole the spring goes in, and then I started looking at the auto decompress, I can't figure out how the darn thing works! It's got a one way bearing, that contacts the spring, and from what I've read that the anti kick back mechanism, which I didn't have that spring in which explains why the dang bike tried to kick my leg off, but I still don't understand the auto decompress and I really want to, its got that lobe, and on my cam there is quite a bit of up and down play on it, but when I hold it to my valve, the actual cam lobe touches the rocker arm and the decompression lobe never appears to touch it, I'm debating if I wanna take it off, but sounds like I need a big press to push the sprocket part off, then I get the whole mechanism, and then I gotta find some way to fill the oil hole, I guess just jb weld.. if everyone thinks these are so so bad and removes them then why does Honda building them with it?

How can I tell if mine still works, and works properly?

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So I tried to get two picks of the up and down play on the decompression lobe, the first on is down, the second one is up, in both the decompress line never touches the valve

1382811920752.jpg

1382811931808.jpg

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I have no idea how it works,,As I said the easiest thing to do so you know it doesn't interfere with the working of the bike is to remove it. .Plenty here disagree believing it to be some sort of saviour,,I don't. You don't need anything fancy to remove it..A vice..a small gas torch ,,a small gear puller..Heat the front use the puller to pull off the sprocket..Once thats off the rest just falls off as a load of bits..Heat the sprocket..tap it back on ,,Fill whatever hole that's left that needs plugging with whatever you want,,I used a bit of a copper nail firmly tapped in.It's going nowhere.Job done.

 

Their's a load of stuff in the manual to do with tolerances etc on that mechanism.. If you want it on I guess check all that then put it back together and hope it all works.. :devil:

Edited by Horri

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Eventually I want a hotcam, just can't afford it right now, if I cut the tab would that be bad? Or would I get better lubrication if I just remove it and fill the hole

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Cut the tab off of the rocker? If you remove the auto decomp you also eliminate any noise that it may have been coming from it. Be sure to seal off the correct hole however you decide to do it.

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The factory service manual gives a real good description of how it works and uses illustrations.

 

It works until about 800 rpm,  if the engine idle is set too low it may stall because the auto decomp is activated.

 

I removed the one from my XR650L some tens of thousands of miles ago. Of course the XR650L is electric start only,which I never really cared for. I recently swapped in a XR600R engine and will leave the auto decomp on it until I have a real reason to remove the the cam.

 

My XL600R doesn't have a kickback problem and it doesn't have the device on the cam, but it certainly can kickback if the throttle is opened while trying to start it.

 

On or off, it really doesn't matter because you have the manual decomp. If you don't have the tools to remove it, don't sweat it.

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If the CDI and pulse gen are working correctly, then these engines do not have a tendency to kick back unless the operator is doing something wrong like giving it throttle while kicking. I had an XR250L with an auto decompressor that I hated. The decompressor had been removed from my 600 long before I bought it and I didn't miss it. Now I have a Hot Cam and still don't miss the decompressor.

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Well, I may have been giving it some throttle.. :blink: I think I may have had my timing chain off one link though, took apart, just added everything for the auto decompress, as its off an 08 model so I assumed it should still work, which it does, got the engine running now, but I still have to give it throttle to start and run, if I let off the throttle it'll stall.. may be the auto decompress though.. lol ill be doing a hot cam in this, probably not till next summer though, so ill live with this for now, its got the high compression piston which should go great with the hotcam.. I kinda wanted to get used to riding it with a stock cam first though, just so I could see the difference when I switch

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