Another assembly question

englishwheeler · Full Member Joined: Nov 14, 2008 Posts: 47

I put the cylinders and the head back on. Then lined up the came according to the Clymer's manual. I have the notch perfectly vertical with the coordinating mark on the rotor indicating TDC.

I then took the slack out of the cam chain and riveted the link. Checked my marks and they're still good.

Next, was the valve cover. Put that on and noticed that the LEFT cylinder valves are both open. I thought that the manual stated that both the intake valves should be closed when the piston is TDC?

Is this correct or did I do something wrong? I know the cam and pistons are aligned according to the manual. Just don't know what I'm supposed to see as normal.

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

When you install the top cover, all the adjuster screws should be backed way off so you don't exert any pressure on any of the valves. This eases cover fitment and torquing. With the cover fitted and the valves set to spec, at TDC one cylinder will have both valves closed and play in the rockers. The other will be forcing the exhaust valve open slightly and the intake will be closed but nearly ready to start opening.

In other words, there will be no play in the exhaust rocker and little if any on the intake. Even though the intake is closed, it's rocker is already starting to run up the approach ramp on it's cam lobe, clearance has been taken up and it's getting ready to open. It doesn't sound like you did anything wrong, you just need to re-set the clearances I think.

The pairs of cam lobes for each cylinder "Y" off the cam 180° to each other. At TDC, one pair is pointing up while the other points down. The cylinder where the lobes "Y" down will have both valves closed and play in the rockers. The side where the lobes "Y" up will have the exhaust valve slightly open and the intake about to.

englishwheeler · Full Member Joined: Nov 14, 2008 Posts: 47

I think you've hit it exactly 5twins! Looking at your picture, I see exactly what I saw when reassembling. You picture was taken viewing the left exhaust opening...correct? My cam looked to be in that same position. When I put on the cover, I noticed that on the right cylinder it sat down nicely. On the left side, it was popped up a bit. When I was tightening the bolts, this gap came out and I noticed the valve springs compressing slightly.

So I should go back and back off the valves and then readjust them and see what I've got? So I won't need to take anything apart again then?

Also, I asked John about this...my new MikesXS cam chain guide appears to not set perfectly centered. I didn't remove the came so it sets as it did 7000 miles ago. I took my calipers and did a depth measurement from both outside edges of the head to the edge of the cam bearings...I have an '81 Special....The measurement differed only .010"...which would mean moving a total of .005". I can't imagine trying to move the cam that minute of a measurement. If I'm wrong...please say so.

I appreciate all this help! I hate being a newb to engines

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

Yes, the picture was taken from the left front so the left exhaust is in the foreground. To center the cam (which centers it's sprocket), with the bearing pairs pushed fully on both ends as far as they'll go, measure how much the bearings are inset where they rest in the head and make it the same on both sides.

The front guide has some play in it's mounting bolts and that is used to center it on the chain. Usually, if you center the guide in the tunnel when mounting it with the cylinder off (measure top and bottom so it isn't cocked) and once the cam is centered, everything lines up properly.

You shouldn't have to take anything apart again unless you maybe find the cam way off center. Even then, you may just be able to loosen the top cover and tap on the cam bearings (inner races) to center it. Yes, do a routine, regular valve adjustment. Set one cylinder then rotate the motor 360° and do the other.

englishwheeler · Full Member Joined: Nov 14, 2008 Posts: 47

Got everything centered now. Took the top cover back off and rechecked the cam for being centered. Also I checked the front chain guide. Got that centered as best I can too. Think I'm nearly there now.

One quick thing. Has anyone ran into as much trouble as I'm having with removing the old gaskets. I've spent more time scraping at them with a razor blade than I have assembling the engine. Just wondered if there's a trick I don't know about.

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

Yes, removing the old gaskets is one of the hardest parts of the rebuild process. I know they sell specific chemical gasket removers but since I have it around for stripping the clear coat off the alloy parts, I just use that same paint stripper. Paint some on, let it soak 5 or 10 minutes, and gently scrape off the softened portion of the gasket. Several applications are usually needed but it does work and it does let you avoid damaging the gasket surfaces by scraping too hard.

What Happened to 650rider.com?

Yamaha xs650