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head swap xr600r need info

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Going to swap a head off 1998 xr600r onto my 1985 xr600r. Would like to know if cam and cam chain will need changing. All ready know about carb alinement problems. Mounting a FCR 40mm carb. The dual carbs have a problem with sticking after getting warm up. Just bought it 3 mouths ago and he had the same problem that why he rebuilt them.

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Yes, everything above the engine cases is different.  You'll also need to change the cylinder, or to retap your existing cylinder to the larger head bolts.  Also a different cam and, I'm pretty sure, valve cover.  The single carb top end also uses a different (thinner) timing chain and matching sprockets.

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I wonder about those head bolts or whatever ones it is that are different..Kinda think it'd be easier just to get new bolts or use the other bolts that fit the proper threads rather than mess around with tapping stuff out..I can't see them being any weaker than the other bolts..

 

If I'm confused and using other bolts from the model that fits the originals threads won't work please put me right..

 

Think the below is Headtraumas stuff,,I'll chuck it in for reference..

 

XL/XR600 83-87 engines have smaller head bolts(8mm) than '88+ (9mm). The dowels are necessarily larger as well. Fitting an '88+ head on an '83-87 jug would require stepped washers under the bolt head and either stepped dowels or opening up the cylinder holes to fit. The cylinder base bolts are the same, though, so an '88+ cylinder could be used instead.

 

Basically my reading of that seems to indicate,,step the dowel and you can use the same bolts you had originally???Yes/No..??

Edited by Horri

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Ya you would use the 8mm bolts but there would be 1 mm(.03937") extra clearance around them in the head, hence the stepped washer statement. It just wouldn't work the other way around without drilling. The dowels would need to be 1mm smaller on one end than the other for proper lineup. 10mm to 11mm? or 9mm to 10mm? can't remember what dia those are.

Edited by jjktmrider

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So if he used 88+ cylinder, head, rocker cover, cam, both cam drive gears and chain, then he should be good. As long as cylinder, piston and ring sizes are correct and in good shape.

 

Does that sound right?

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The motor that's currently in my bike is an old twin carb motor (85ish) with a single carb head (96ish).

 

You can use your cam chain but you will need re-use the gear from your old cam and flip it over to get things to line up.

 

I think i took one of the bigger dowels and cut it in half and used the halves to sleeve down the larger dowl holes in the head.

 

I didn't do anything with the head bolts as I figured the dowels would be enough to hold it in place and I've got quite a few miles on it with no issues.

 

Hope that helps

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"genair1" don’t know your mechanical abilities but I’ve never seen step dowels for sale which means you make or have someone make two of them 10m/12m outside diameters, inside diameter clearance for head bolts, paper thin for the 9m head bolts. These dowels locate the head gasket and head to the cylinder bore. The simplest option is base cylinder gasket up and either flip original cam sprocket or change crankshaft cam chain sprocket.

 

"HJ"      :cheers: 

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The motor that's currently in my bike is an old twin carb motor (85ish) with a single carb head (96ish).

 

You can use your cam chain but you will need re-use the gear from your old cam and flip it over to get things to line up.

 

I think i took one of the bigger dowels and cut it in half and used the halves to sleeve down the larger dowl holes in the head.

 

I didn't do anything with the head bolts as I figured the dowels would be enough to hold it in place and I've got quite a few miles on it with no issues.

 

Hope that helps

That makes sense to me,,Pity we don't have someone around with the two different dowels to see what they fit inside each other like..I reckon that's all that's needed..Can't see the head shifting around just because a bolt has an extra mil either side of the bolts once they're tightened to spec,,Take a hell of a lot to shift that head about..

 

Yep and right about the Camchain and sprockets,,Just need to reverse the way that top sprocket bolts on to the more modern cam and it all works..Think that's what I did in my current bike as I noted when doing the clutch the other day that it's using the thicker chain from the older 600s

Edited by Horri

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It's been a while since I had a dual and a single carb engine disassembled next to each other, but I think I remember the cylinder head bolts also being different lengths or having different lengths of threads.   I remember there being some reason why it wouldn't be a clean mod to simpy retap the treaded holes.

 

I think the alignment dowels are mostly to get everything aligned before the bolts are tightened down.  If they're not a pretty tight fit, all the various parts might not mate squarely.

 

Many people have posted that dual to single carb conversions don't really work because the single carb hits the frame's upper shock mount.  If that isn't solved, then engine part compatability is moot.

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Throw a 650L intake manifold on it then,,that'll no doubt sort the frame business..

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I'm pretty sure the 650l frame has the same offset shock mount as the 600R.

 

Most of the dual-to-single carb swaps I've read about didn't work, but they all tried to use the 600R carb.  You might be the first to try it with the FCR carb, which has the throttle drum on the other sie.  Possibly it might work.

 

You'll need a 650L intake manifold and a 650L air box boot (or complete air box/boot assembly).

 

Unless your 600R frame is special, e.g. it has a street title, there's not much point in using it.  Just get a 600R or 650L chassis and swap parts over.

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