Top end questions

Metal

Metal

XS650 Custom shop
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Hey guys,
So Pulled my head off for the first time since I got this motor. At hi revs I could hear a big tapping sound. I thought it must be the cam guide or the head gasket. I have oil leaking out the head gasket so I figured it was a blown head. Looking at the pictures what do you guys think?

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What I found was some galling on the cam lobes. Id like to know what people think of this wear?

The other thing is it was missing some seals around the head bolts, should I remove and replace or just clean up and replace the seals. I have know idea what this seal is called if anyone knows?
 
I'd say that cam is toast. That tube w/ o-ring you're holding in the last pic seals the outside stud holes. I see two in your pics. There should be 4. Maybe the other 2 have remained stuck up in the top cover. Usually all four do. It looks like someone has been in there before, and not someone who knew what they were doing from the looks of things.
 
OK fellas some progress. I took the head off and sourced a donor engine from a friend. Turns out the motor I own has much bigger pistons and a way different cam.

So first thing first help me I.D what I have. My cylinder diameter is 80.5 mm.
The cam that's gauld has the following engravings PCH WEB CAM #84AB

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As the cam from the motor is worn out can I put a stock cam back in with my over sized piston kit?

There are some slight marks on one of my valves. More so just carbon scatched.

I'm going to have to re use my head gasket. Seems ok. I'll need to order a new one.
 
You don't re-use head gaskets. You replace cam chains and front guides on 30 year old motors. Admit it, you're the guy who was into that motor in the 1st place, lol. That's why it's all messed up to begin with.
 
750cc kit headgaskets are available, like from mikesxs. Can't tell well from the pics, but are there any dished rocker followers? You may have lost lubrication to the top end at some time, gotta check that. The cam looks like a fairly aggressive reweld/regrind, the weld material may have failed, not too uncommon in the old days...
 
I know its bad form to re use a gasket. But it looks like its brand new still. Someone was just in this motor before I got I'm sure of it. I'll run it over the weekend and replace it asap. Yes top end lube problem was my thought as well.

I replaced the 35 year old studs and replaced the stud head seals.

From the diameter I should be able to find out what size piston I have right? Anyone know some online reference?

I'll replace the oil feed tube and blow out the head. I had the oil pump out and it looked good.

The crazy can explains a lot about the motor. For one it was real hard to get the points to open right and it was great open throttle but lagged a lot at low revs.
 
You can look at the 750 kit piston offerings on mikesxs, heiden tuning, hoos racing, MMM Michael M Morse. Try searching on those terms, and look into this forum's 'links' section.

80.5mm should be 2nd over 750 pistons...
 
OK, your motor appears to be an early 256 type. That other cam you got looks to be an '80 or newer 447 type because it has no bushings in it for the advance rod. The two types won't swap because the cam chain sprockets differ, in both size (# of teeth) and pitch. Your donor engine is probably a newer 447 type. To use parts of it to fix yours is possible but you need many parts. You would have to swap the crank, pistons, cam, cam chain, cylinders, cam chain tensioner .... honestly it would be easier to swap the whole motor.
 
Ah that bums me out. Oh well I'll just put it back together until I get a new cam. Can I use the rockers from a newer engine. Yes mine is a xs1.
 
Yes, I think the rockers will swap. The cam can be made to work but it involves pressing the sprocket off and swapping the older one on. Usually the opposite is done because the older cam is hotter - but yours is no good so so much for that.
 
5twins said:
OK, your motor appears to be an early 256 type. That other cam you got looks to be an '80 or newer 447 type because it has no bushings in it for the advance rod. The two types won't swap because the cam chain sprockets differ, in both size (# of teeth) and pitch. Your donor engine is probably a newer 447 type. To use parts of it to fix yours is possible but you need many parts. You would have to swap the crank, pistons, cam, cam chain, cylinders, cam chain tensioner .... honestly it would be easier to swap the whole motor.
Click to expand...

Confirmed, I'm counting 34 teeth on the old cam (256 type), 36 teeth on the other (447 type).

So, the crank would be 256, with the larger 22mm wristpins. Just like my setup. Very difficult to find performance parts for these. Maybe you could find a cam grinder that'll renew your cam...
 
OK this is where things get weird I have a 36 tooth cam! But this is a xs1 engine. I think I may have a little hotrod. So this mean I can use the spare cam. Only problem is getting the bushings and needle bearings out of the warn one into the fresh one. Any one know a good technique. Also been wondering how to remove the rocker arms.
 
Yeah, `70-`71 stuff seems to be gold-plated these days.

I thought about doing an interesting cottage-business awhile back. You send me your XS part, I place it on my XS1B's seat for a few minutes, then send it back. You then put it on eBay with the declaration: "Came off a `71 XS1B!" Fast money...
 
TwoManyXS1Bs said:
Yeah, `70-`71 stuff seems to be gold-plated these days.

I thought about doing an interesting cottage-business awhile back. You send me your XS part, I place it on my XS1B's seat for a few minutes, then send it back. You then put it on eBay with the declaration: "Came off a `71 XS1B!" Fast money...
Click to expand...

Classic. :laugh:
 
Metal said:
OK this is where things get weird I have a 36 tooth cam! But this is a xs1 engine. I think I may have a little hotrod. So this mean I can use the spare cam. Only problem is getting the bushings and needle bearings out of the warn one into the fresh one. Any one know a good technique. Also been wondering how to remove the rocker arms.
Click to expand...

Double check your tooth counting, 34 is the 8mm pitch 256, 36 is the later 447 type.
You may be able to get a machine shop to press-off the sprockets and swap, not for the faint-of-heart...
 
Well, you could have a 447 crank swapped in there. That's common because, as mentioned, hop-up parts are easier to come by for the later motors.
 

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