Cam shaft question for the gurus

[dbeardslee]

I've got another member's '79 SF out in my mancave with the head off. When I pulled the cam shafts I noticed that they're not marked the same way as my '79 F. The 'F' has 2H7 printed on the shafts, while this SF has '95' printed on the intake shaft, and 8Z printed on the exhaust shaft. Is that the correct marking for an SF, or has somebody been diddling around with the cam shafts?

[bikerphil]

I've seen a few sets of XS11 cams with all different numbers and letters embossed in them. Couldn't make anything of it either.

[mro]

SF cam …

SF cam …
Intake 36.805 tall, 8.805 lift, 28.341 dia. (mm)
Exhaust 36.305 tall, 8.305 lift, 28.341 dia. (mm)

mro

[dbeardslee]

The bikes owner got it from her father who was the original owner, and she didn't say anything about him changing the cams. The rest of the bike is stock, so they're most likely the ones that came with the bike. I probably would have been better off not looking at the markings, but since I've already contaminated myself I think I'll check them against MRO's measurements .

[DGXSER]

I swear sometimes we must be related Doug. I know as sure as I am breathing those are the stock from the factory cams in there. But I am just as sure if were sitting in my garage, after reading those numbers, I'd have to measure before I could sleep.

[dbeardslee]

I'd have to measure before I could sleep.

I just did it - man I hate being predictable . I used a caliper (it's not metric, so I had to do a conversion) to do the measurement, so it isn't ultra accurate. Should be close enough for government work, though. Here's what I got -

Intake ht - 36.7792 mm Intake dia - 28.321 mm
Exhaust ht - 36.2712 mm Exhaust dia - 28.3464 mm

Considering the measuring device, and 30 years of wear, I'd say it's a pretty good match with MRO's numbers.

[trbig]

Turn the cams over.. 2H7 is probably on the back side.

All of them I've ever had apart had either that 2H7 or 3H5 stamped on them somewhere. First I've ever heard of those numbers. I hope you checked the valve shims before you pulled the cams out.. Sure makes it easier to change them.

Tod

[dbeardslee]

All of them I've ever had apart had either that 2H7 or 3H5 stamped on them somewhere.

Me too, which is what threw me on these. The intake has '95' where the 2h7 normally is, and the exhaust has 8Z in that location. The SF's have a screwy mechanical advance that advances five degrees less than the E and F models. Maybe that's got something to do with these cam shafts.

I hope you checked the valve shims before you pulled the cams out.. Sure makes it easier to change them.

Why? Shims are still in the buckets, the buckets are still in the head, and the head is sitting on the floor in the garage. I'll check them before I put the cams back in though. Now if I was to turn that head upside down it could be a problem .

Maybe I should tell the whole story on this machine. The owner took it to her local motorcycle expert. He told her he replaced the rings ($300 for a set of rings - just the parts!), reworked the head, went through the carbs, and charged her $2400. When she went to pick it up, he was showing off his handiwork and twisted the throttle hard. Something let go and it started blowing smoke and running bad. Compression on the #1 cylinder went way down. She got the bike back from the guy (after diving through a car window after him - she's a pretty tough little gal ), and parked it in her garage where it's been for a year or so.

She trailered it over here, and I pulled the head last weekend. Originally we (the swoxs conglomerate) thought her mechanic put the rings in wrong, but as I've taken this thing apart I've been pretty impressed with this guys work. With the exception of the head gasket that looked more like the old kind than the new kind except the big rubber seal wasn't installed. I did some damage to the integral crush gasket around the number 1 cylinder when I removed the head, but it looks to me like there was other already-there damage to the gasket.

Additionally, when I removed the head, it didn't take too much torque to break the bolts loose, and I wouldn't be surprised if they hadn't been retorqued after the motor had gotten hot and cooled down. Anyway, I'm thinking the head gasket is what let go. He evidently had some problems getting the cam chain back in too, which immediately made me wonder if he bent a valve. I was going to pull them all and spin them in a drill press to make sure they're straight, but now I'm thinking I might do the gas-in-the-upside-down-chamber test to see if they're leaking.

What are the master's thoughts on the gas test vs. pulling the valves out?

[Guy_b_g]

If he bent a valve damage should be visible either on the valve or the top of a piston.

Gas in the chamber check is a good idea though, and should tell you what you need to know (especially about the valve job he gave it, if any).

[dbeardslee]

Actually, the head looks really good, which is why I'd rather not take it apart. Top of the pistons looks good, and the valves look like they're sealing, but I haven't had my eyes calibrated in a while . I think I'll put some duct tape over the buckets, turn it upside down, and try the gas test.

Here's what the owner had to say regarding compression - "Compression is140 on #3& 4 cyclinders 125 on #1 & 110 on #2but not sure rings have had time to reseat. Smoke comes out right exhaust pipe when bike has warmed up..not sure what problem is there." She also said the test was done on a cold motor.

[Guy_b_g]

Just leave the head upside down and put the gas in the chambers...much easier. oops, (misread what you're doing...keeping the buckets on..sorry)

Thought for a sec...nevermind..lol

[DGXSER]

I would do the leak test. See what that tells you. I forgot all that detail abotu the mech hitting it so hard right after the work. I'd bet your right on the head gasket. I'm crossing my fingers for you on it. Wish I could come over and help, I hate being a gimp!!!

[dbeardslee]

I hate being a gimp

But it makes you so much easier to find .

misread what you're doing...keeping the buckets on..sorry

Seems like every time I remove buckets, I get one or two that just don't want to go back in. Then I have to take the valve out and go to work with the brake cylinder hone, and I'd rather not go through that if I can keep from it. The first one I did, I turned upside down and it sounded like little tin rain drops - hence the duct tape .

[trbig]

I doubt you'd see anything from a bent valve on either the valve or piston in a brand new motor. Others, you can see an imprint in the carbon on the piston with sometransfer of carbon onto the valve, but a freshly rebuilt one.. I doubt you'd see it. The valves bend so easily, that it's doubtful you'd scratch or mar a piston with it unless it brok off and fell down into the chamber.

Definately way easier to do the gas in the port check versus pulling the valves out.

Also, you may already know, but when checking the valve clearances on the bench, you'll need to prop the head up on a couple 2x4s away from the valves. When you spin the crank to check clearances, the valves will bend on a workbench. At least.. that's what TC tells us..

Also, just one cam at a time. With the one holding a valve open while you spin the other, one side could hit the other that's held open. "Not enough room in this town for the both of us!" you might say...

Tod

[dbeardslee]

I'll probably adjust the valves with the head on the motor - just faster for me to do it that way. Besides I might get lucky and they may be set correctly. If I have to change some, I've got this little puppy on loan - are you ready to drool?