XS650 Top End Buildup

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This thread details the reassembly of the top end of my 1980SG. Everything's already cleaned up and measured, but I'll backtrack a little and show how to do some measurements. All manual references used here are from the 1978-80 Yamaha Service Manual. All points of view (left and right, fore and aft) are referenced to the riders point of view

I'm writing this for anyone who's never done a top end before. If you have, you probably won't learn anything new.... or maybe you will. Keep in mind, this is how "I" do it. If you do something different that will add to the usefulness of this thread, by all means jump into the discussion.

Before we get started, you need to check the big and little ends of your connecting rods. I did this while the bottom end was disassembled and unfortunately, didn't take any pics of it. Pg. 27 of the manual tells you what to check for and the dimensions. You need to do those checks before starting the top end reassembly. If you can't figure out how to do it, bring it up in the comments and I'm sure someone will do some 'splainin'.
Let's get started.

First off: Sealant. I use Permatex Aviation sealant....

View attachment 118239


The brush inside the cap is a little unwieldy. I use a Q-tip for better control and less mess. I've overhauled or repaired hundreds of engines in my career and this is all I've ever used. It's never let me down. If you prefer Yamabond or some other sealant... then by all means, use what works for you.

Since you already have the top end apart, now would be a good time to replace your stretched out cam chain. Use a piece of safety wire to join the new chain to the old one and work it into place.

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Once the chain's through, use some safety wire to tie both ends together and tied to one of the studs. Ya don't wanna lose it back down in the engine... :(

The next thing I did was install the cam chain tensioner. It's a new one from Mikes because I couldn't find an OEM one. I hope I don't come to regret that. There's 2 long and 2 short screws. The long screws go on the right.

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The 4 screws are JIS... not phillips. A phillips screwdriver will strip the heads. You can modify a #2 phillips by grinding the point like this.....

View attachment 118242

I find that this works just as good as a JIS screwdriver. Oh... and I put a little blue Loctite on the screws, then tighten to 85 in.lbs. If you're worried about dropping screws and washers, do it this way....

View attachment 118243


Next, make sure the two alignment bushings are installed (red arrows) and install the base gasket.

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I know some people don't use gasket sealer here, just grease or oil.... I do. Just make sure you get it on the right side/bottom of the gasket so you're not makin' a mess as you go (test fit it if you're not sure. It only fits one way). Make sure you re-secure the cam chain after you slide the gasket down. Rotate the crank so that the connecting rods are up at TDC and secure with rubber bands as shown. This keeps the rods centered as you install the pistons.

OK, on to the cylinders. I like to hone them right away and do all the measuring afterward. Honing knocks the glaze (shine) off the cylinder walls. This gives a scratched surface that aids in ring seating and in oil retention (lubrication). There's tons of videos out there if you've never done it before. Seems everybody has their own techniques and opinions on the best way to hone a cylinder. I've found this short one that does a fair explanation on how to do it.


You can look at some of my pics below to get an idea of what the end result should look like. If you've never done this before, it might be worth getting an old cylinder and practicing first. It's up to you.... If, after honing you still have score marks in the cylinder, you might want to put a good pic of it up in the comments and let the "gurus" here give you their opinion on whether they're acceptable or you need to do an oversize bore job.

Providing the honing process went good, now's a good time to install the big o-rings in the bottom of the sleeves (top arrow) before you forget em.

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The bushings for the cam chain guide, technically called guide bar nuts (bottom arrow) have copper crush washers for oil sealing. There's several ways you can go here.... your best bet is to install new ones. Or you can use a torch to anneal them....

View attachment 118247

All it takes is a propane torch to heat them to a bright orange and then quench them in water (thanks Dick). Don't hold the heat on em' for too long or they'll start to deform/melt on you. Now they're soft again and can be re-crushed into an oil tight seal. Your third choice is to spread a little sealant on the threads and torque em down. any one of these will work just fine for oil sealing. A word of caution here: There were reports in the past of the MikesXS bushings being too long, causing the cam chain guide to stick too far into the cylinder. If you're using aftermarket bushings, measure 'em against the originals and make sure they're the same.

OK, assuming you've got your cylinders all cleaned up, it's time to check them for serviceability. The next thing we're gonna' do is check the bores for excessive wear, roundness and taper. You'll need a telescoping gauge (usually just called a "T" gauge) and either a micrometer or caliper that can measure down to 4 decimal points (this is all written for inches, not metric). I've found that even many seasoned mechanics don't know the correct way to use a T gauge, so I've made a short video showing the correct way to use it.


Your manual (Pg. 26) has the dimensions and tolerances you're looking for and a picture showing where to check. There's 6 places to measure... towards the top, middle, and towards the bottom, then again at 90deg. to the first checks. From these measurements you can determine taper, roundness, and diameter. Write these down.

Now measure measure the piston skirt as shown on Pg 26. I use a wooden block dropped down inside the cylinder to rest the piston on for this check.

View attachment 118248


This dimension, subtracted from the bore dimension (I use the mid point measurement for this) gives you your skirt clearance dimension. The specs. on Pg. 64 give a skirt clearance of .002" to .0022".

Lets talk about cylinder, piston and ring matching briefly. No two pistons are the same.... no two cylinders are the same... no two rings.... well, you get the picture. Measure both skirts and compare them to both cylinders.... then decide which piston is left and which is right. Think balance..... If one skirt is at the minimum and one at the maximum..... and you swap the pistons and now both are towards the max. but are the same..... Which configuration do you think is better? Exactly... you want balance. Do the same for the rings (next section). Mix and match until you can get the best balance of ring gaps.

An alternate way to check the skirt clearance is to use a feeler gauge.

View attachment 118249


With the piston pushed to about midway into the cylinder (correctly oriented), a .002 feeler should be a snug fit and a .003 should immediately start to bind up as you insert it. I prefer to use tapered feeler gauges for this, but mine seem to have grown legs...:(

View attachment 118250

OK, now let's see how flat the face is. You need something absolutely flat and rigid. I use a piece of 7075T6 aluminum angle.

View attachment 118251


Move it around to various places on the face and see if you can slide a .001 to .002 feeler under it at any point. If you can, you might want to consider refacing it. I'm not gonna cover doing that here, but if you need to do it, bring it up in a comment and I'll (or someone else will) explain how to do a "backyard" refacing.
If all these checks are good, you are now the proud owner of a serviceable set of jugs. :)

I'm guessin' I'm about to hit my character limit on this comment. So, we'll continue below on the next one.
Great information just about to start stripping down my top end,smoke on left cylinder guess valve stem seals gone.👍
 

Oldnwiser

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I have been wrenching myself for many years before freshening my XS2 back when my wife and I married 42 years ago and later on a 447 76 engine that I built for my 83 bobber that had sat outside for 10 years by the previous owner. I loved having the sleeves slightly bored and power honed in a good fixture and finishing myself on their CK-10 to a nice plateau hone, I was lucky to find forged 702 cc pistons and a little planing on the jugs and head brought the cr to 9.25. The r/s of the 256 we as 1.88 if remember right. The trans was perfect as was the clutch and the cam guides. The engine was a well maintained one, But as always you want good ring seal. Though these were forged they were light and rare to have 22 mm car like pins . I used single spirolox on each side of each piston. The rings were narrower than stock too. I used the stock XS2 cam and made sure to keep the chain on the loose side of spec lash.006/.012. 2 ply head pipes 1 5/8 inside 1.75 out and the old bullts. BS38S set rich and the timing just righ at 36 total. I f I could only ride it one more time, it was smooth and beastly at the same time. It revved so quickly and a flick and it was just so sweet sounding. I am 62 now and I have a .020 over 390 FE that hits like that. I still wish I could see to drive and ride.
 

Oldnwiser

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Something I missed? :zzz:
I lost most of my vision a few years ago. I used to ride and race, and years of wrenching, picturing each step of a very good discription of a project really makes me miss my projects I have done. I can still put an XS together and a Ford FE, but I had to surrender my license. I really loved building the 360 degree engines, but I would still love to build a 277/83 and put it in an XS2 for my 40 year old son to ride. Muscle memory I guess, or something else, lol.
 

jetmechmarty

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I lost most of my vision a few years ago. I used to ride and race, and years of wrenching, picturing each step of a very good discription of a project really makes me miss my projects I have done. I can still put an XS together and a Ford FE, but I had to surrender my license. I really loved building the 360 degree engines, but I would still love to build a 277/83 and put it in an XS2 for my 40 year old son to ride. Muscle memory I guess, or something else, lol.
I’m sorry you have to deal with that.
 

Kevin Werner

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I lost most of my vision a few years ago. I used to ride and race, and years of wrenching, picturing each step of a very good discription of a project really makes me miss my projects I have done. I can still put an XS together and a Ford FE, but I had to surrender my license. I really loved building the 360 degree engines, but I would still love to build a 277/83 and put it in an XS2 for my 40 year old son to ride. Muscle memory I guess, or something else, lol.
When my sight became "challenged" I got an XS650 before it became critical. I have been able to share rides with @jetmechmarty , @gggGary, @desmoman900 and others (I don't know their
forum signs but cherish our times). My sight is actually improving, a temporary impairment, but if the situation returns I will know that I had the chance to enjoy one of my bucket list items. In the mean time, I press forward on the "Red Bike".
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Oldnwiser

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Thanks everyone. I still hope I can help other people with their bikes. We have a great community here and I really appreciate the opportunity to use what I have. I love the sound of both the 360degree and the 277 rephased bikes. I hope to help contribute all I can!
 

Oldnwiser

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Btw, if you’re having electrical problems I have found close to 99% of the times it is a ground issue. Make sure that the surface is bare and the wire has continuity and use a star washer to connect it. I have gotten in a hurry doing a top end and just reconnected the grounds to the chassis that has sat around and reused the star washer and kicked until ready to puke and drank another beer and thought GROUNDS STUPID. Go through and do them right at 1:00 AM and do them right including oxidation on the case and one kick Shazam! Isn’t it great when a plan comes together. I kept star copper washers along with points in a bag under the seat. Lol hope this helps.
 

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If you see obvious problems in this thread, by all means point them out and I'll correct them.... I never claimed to be a tech writer. ;)
I wrote this in the Lab over the course of several weeks, so some of the mistakes have already been pointed out and corrected. There's several links that directly pertain to this thread. Gimmie a few days and I'll get 'em up here.
Thanks to TwoManyXS1Bs, 650skull and gggGary for their valuable input
Edit 10/6/18: Some useful links written by other forum members and provided by the above gentlemen...
Discussion of piston installation (with videos).
Complete engine rebuild.
Discussion on front guide replacement
Hi Jim; First, what a great post - thank you for all the time and wisdom you’ve put into this. I read over coffee this morning out of pure interest and loved it. However, I noticed in one of your images the internal oil baffle located in the head - the formed piece of steel that is inserted. This caused me two reactions: the ah ha moment when you recognise where the piece on the bench goes & the second, natural expletive when you realise that it is still on the bench with the engine fully assembled and back in the frame. I think the word rhymes with “duck”. So, my question is, what is the implication of not having this installed? Is it a drop dead vital necessity that I remove the engine to install? I know it should be there and the nice men at Yamaha want it there, but what would be the implications of leaving it out? I realise not ideal or optimum, but if I can, I will!
 

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Hi Jim; First, what a great post - thank you for all the time and wisdom you’ve put into this. I read over coffee this morning out of pure interest and loved it. However, I noticed in one of your images the internal oil baffle located in the head - the formed piece of steel that is inserted. This caused me two reactions: the ah ha moment when you recognise where the piece on the bench goes & the second, natural expletive when you realise that it is still on the bench with the engine fully assembled and back in the frame. I think the word rhymes with “duck”. So, my question is, what is the implication of not having this installed? Is it a drop dead vital necessity that I remove the engine to install? I know it should be there and the nice men at Yamaha want it there, but what would be the implications of leaving it out? I realise not ideal or optimum, but if I can, I will!
Hi Crashed,
first... thanks for the kind words. I wrote this for a forum member who had never put a top end together. So I tried to write it in that frame of mind. He's left us now but this thread still gets plenty of mileage. Robin would be pleased at that. To your question...

You're not the first person to leave that baffle out. And I recall some folk just left it that way and ran without it. Worst case, you'll get a little more oil out the breather than you normally would. In short, it's not the end of the world.

If it were me (who forgot it), I would not tear the top back down. I'd get a hold of a stainless steel scrubbing pad.... the kitchen type, and stuff some of that in the breather outlet housing. That would likely catch any oil... and there's a drain hole at the bottom of the housing that will return the oil to the sump. I think that would work just as well as the baffle... if not better. And it could be serviced without removing the engine if needed.
 

Crashedkiwi

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Hi Crashed,
first... thanks for the kind words. I wrote this for a forum member who had never put a top end together. So I tried to write it in that frame of mind. He's left us now but this thread still gets plenty of mileage. Robin would be pleased at that. To your question...

You're not the first person to leave that baffle out. And I recall some folk just left it that way and ran without it. Worst case, you'll get a little more oil out the breather than you normally would. In short, it's not the end of the world.

If it were me (who forgot it), I would not tear the top back down. I'd get a hold of a stainless steel scrubbing pad.... the kitchen type, and stuff some of that in the breather outlet housing. That would likely catch any oil... and there's a drain hole at the bottom of the housing that will return the oil to the sump. I think that would work just as well as the baffle... if not better. And it could be serviced without removing the engine if needed.
Many thanks Jim; I shall do exactly that - greatly appreciated. Nice peace of mind, All the best over there !
 

gggGary

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All years of breathers have at least some type of internal baffling as well as that piece inside the head. If you still have the stock airboxes all the 76 and up have the hose go down then back up, to end in the airbox in the intake airflow. Under power any residual oil in the hose gets pulled through the carbs into the cylinder and burned.
 
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Oldnwiser

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Hi Crashed,
first... thanks for the kind words. I wrote this for a forum member who had never put a top end together. So I tried to write it in that frame of mind. He's left us now but this thread still gets plenty of mileage. Robin would be pleased at that. To your question...

You're not the first person to leave that baffle out. And I recall some folk just left it that way and ran without it. Worst case, you'll get a little more oil out the breather than you normally would. In short, it's not the end of the world.

If it were me (who forgot it), I would not tear the top back down. I'd get a hold of a stainless steel scrubbing pad.... the kitchen type, and stuff some of that in the breather outlet housing. That would likely catch any oil... and there's a drain hole at the bottom of the housing that will return the oil to the sump. I think that would work just as well as the baffle... if not better. And it could be serviced without removing the engine if needed.
I made a PCV of sorts for mine , I had the baffle in , but I put a check valve in and used a small reservoir to store vacuum and pulled a vacuum on the crankcase to pull the pressure under the pistons to the reservoir and separate the oil and vent the air out. It worked well and it helped acceleration. I reminded me of early check valves in road draft tubes.
 

Oldnwiser

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Btw, I aimed an oil drain hose from the treservior I made to the chain to be a passive chain oiler. It worked pretty well.
 

Oldnwiser

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All years of beathers have at least some type of internal baffling as well as that piece inside the head. If you still have the stock airboxes all the 76 and up have the hose go down then back up, to end in the airbox in the intake airflow. Under power any residual oil in the hose gets pulled through the carbs into the cylinder and burned.
I found one that had a Y shaped 2 outlet baffle and it really pulled down the crankcase, you could push the kicker down easily and the 2nd one you could push down and feel it getting easier and if you pulled the dipstick you could feel the suction really well with the double breather evacuating the case. I had plumbers nightmare there but it was a free evac and you could feel the difference… A couple 🐎 I have a pan evac I’m my old race car, every little bit helps. The best one I settled on for the bike was a clean reed valve from a Banshee two stroke. I used it until I sold the bike. The 2nd best was a pintle valve and reservoir.
 
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Hi I'm pretty new to the site so I hope I'm posting this in the correct place.
First off thanks Jim this has been a really useful post. I'm pretty close to completing the rebuild on my 74.
I've hit a problem with my camchain master link. I've managed to get the link into the chain on the sprocket. The only problem is I can't get the plate to fit over the pins.
The chain is D.I.D. the master link came with the chain. I'm not sure if I should open the holes in the plate up with a needle file.
Any ideas anyone.
 

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gggGary

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Not an expert, but would NOT open up the pin holes in the plate. Your pic is a bit blurry, is that evidence of staking on the ends of the pins?
Maybe check the pin OD vs the OD of the ends of the pins. They are usually a tight fit, a master link tool often used to send the plate home.
 

Jim

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Hi I'm pretty new to the site so I hope I'm posting this in the correct place.
First off thanks Jim this has been a really useful post. I'm pretty close to completing the rebuild on my 74.
I've hit a problem with my camchain master link. I've managed to get the link into the chain on the sprocket. The only problem is I can't get the plate to fit over the pins.
The chain is D.I.D. the master link came with the chain. I'm not sure if I should open the holes in the plate up with a needle file.
Any ideas anyone.
I would definitely recommend against enlarging the holes.
Sometimes when the chain is real tight, it spreads the master apart ever so slightly... just enough so the pin sides are spread further than the hole edges.
It involves two people.... grab the links on either side of the master and pull (bend) the chain .... like you're trying to collapse it in on itself. While doing that, have someone slip the plate onto the pins.
 
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