Stupid is as Stupid does.

[senrak]

Did a dumb thing today. I figure I might as well share it here with the hope that someone else may not make the same stupid mistake.
I have rebuilt many automotive engines in the past, worked on my share of two stoke snowmobiles, but have little experiance with motorcycle engines.
I figure I got decent engine experience. So okay, I pull the head off this beat up, high mileage XJ 1100 after a compression check shows low compression on #1. Take the head to local machine shop and they do a valve job. Okay, looks good.
I decide that before I re-assemble I should check the valve clearance on the bench, so I re-install the cams and turn them to low spots sticking the feeler gage in. Its going well. The springs are pretty stiff when they have to be compressed, but it's okay. I have a wrench the fits on the 7/8 hex on the cam.
What the heck. One of the lifters, springs, and valves isn't coming back up when I turn the cam. I turn the head over and both the exhaust valve and the intake valve are open and jammed against one another. Oh no. It's a hemi. They occupy the same space when open! Result, ofcourse is two bent valves. They don't seal unless I tap them onto their seats. Will need to go back to the machine shop, and I am sure I'll be in need of 2 new valves and more machine work. There goes another 100 bucks.

[motoman]

Did a dumb thing today. I figure I might as well share it here with the hope that someone else may not make the same stupid mistake.
I have rebuilt many automotive engines in the past, worked on my share of two stoke snowmobiles, but have little experiance with motorcycle engines.
I figure I got decent engine experience. So okay, I pull the head off this beat up, high mileage XJ 1100 after a compression check shows low compression on #1. Take the head to local machine shop and they do a valve job. Okay, looks good.
I decide that before I re-assemble I should check the valve clearance on the bench, so I re-install the cams and turn them to low spots sticking the feeler gage in. Its going well. The springs are pretty stiff when they have to be compressed, but it's okay. I have a wrench the fits on the 7/8 hex on the cam.
What the heck. One of the lifters, springs, and valves isn't coming back up when I turn the cam. I turn the head over and both the exhaust valve and the intake valve are open and jammed against one another. Oh no. It's a hemi. They occupy the same space when open! Result, ofcourse is two bent valves. They don't seal unless I tap them onto their seats. Will need to go back to the machine shop, and I am sure I'll be in need of 2 new valves and more machine work. There goes another 100 bucks.

Your not the first..............low compression on #1 and pull the head before checking valve clearances....oopps #1. New valves......not happening from mother Yammy. Head sitting flat on bench with nothing under head to space it from benchtop doing valve clearances....ooppps #2, bent valves. BTW, with four different cut angles in head, mimicks a hemi upon conbustion without the center 'hotspot'........so least U got part of it correct and not a total loss, but a good reminder for others.

[Schming]

Hemi...well sort of

The following borrowed from this site: http://www.motorcycleclassics.com/cl...ha-xs1100.aspx




"While hemispherical combustion chambers, with intake and exhaust valves placed across from each other and a centrally located sparkplug (hence the term “hemi head”), were the performance norm, they had inherent limitations. Chief among them was upping compression ratio without resorting to pistons with huge crowns, increasing weight and slowing heat dissipation. To get around this, Yamaha developed a complex “polyspheric” combustion chamber, a design that required six machining operations to achieve. The multitude of cuts and shapes milled into each combustion chamber produced the same volumetric efficiency of a hemi but without any of a hemi’s drawbacks, allowing Yamaha to use slightly crowned and lighter weight pistons (211 grams)."


Read more: http://www.motorcycleclassics.com/cl...#ixzz2DbjR7tb1

[natemoen]

DTDT.... as said already, you are not the first and will not be the last. I took out more than 2 valves doing the same.

[DGXSER]

Yep, timing, such a simple concept and yet so complicated in application. Since I have not had the pleasure of pulling a head off one of these beast myself, though I have helped in the process a couple times, have not made that error. But as had been said, your in good company with more than a few who have. Only one cam at a time is the method when they are not connected and in time. That and elevated off the work surface as Moto stated.

My fav saying is "I like to learn from other peoples mistakes. Much more pleasant than learning from my own."

[bikerphil]

In case you need a reasonably priced part source for valves for your '82 motor, scroll down on the page, 4th from the bottom...

http://www.newmotorcycleparts.com/mo...ts/valves.html

[GLoweVA]

In case you need a reasonably priced part source for valves for your '82 motor, scroll down on the page, 4th from the bottom...

http://www.newmotorcycleparts.com/mo...ts/valves.html

+1 on what Phil said, I ordered an exhaust valve from those guys and it works great. (not too bad a price either)

When I got my SG, #3's valve clearance was way huge! (like .45mm). I figured the valve wasn't coming all the way up and seating, so I checked compression in #3 and almost zero, so I knew I had to pull the head off. When I had it on the bench, I could see a half cresent light shining thru the exhaust port.

Ordered a new vavle, put it in, did a seat check with some magic marker/dye stuff and full contact area, put springs in and remounted the head and compression is back to normal.

[clcorbin]

Welcome to the club! I did the exact same thing for the exact same reason a couple of years ago! It sucks!

On the bright side, it is a LOT funnier a couple of years later when you read someone ELSE did the same thing... Not so much at the time of the event though...

[senrak]

In case you need a reasonably priced part source for valves for your '82 motor, scroll down on the page, 4th from the bottom...

http://www.newmotorcycleparts.com/mo...ts/valves.html

Thanks for the link, Phill.
Called down to Indy this morning. Two valves on their way for only $48.95. At least they are still available!

[bikerphil]

No problem bro, good luck with the rebuild.

[MPittma100]

Valves

You should take the cams, caps, and lifters (buckets) with you to the machine shop. Let them adjust the valves for you without shims. Just give them the lash specs. A competent shop can do this. If they cannot, take it elsewhere.

MP

[DGXSER]

MP, I do not see the point of that. You need some shims in there, the buckets are way to deep for a stock sized valve without the shim. And some time down the road you will need to reshim anyway as the valves wear into the seats. So I do not think you will have any benefit of machining the valves. Besides, that is alot of money in machining time compared to changing some shims.

[crazy steve]

You have to have the shims in there for multiple reasons, but the big one is the metal the shims are made of is compatible with the cam lobes. Use the wrong metal against the cams, no cam life and probably a dead motor...

[WMarshy]

I second that. A member gouged his cam lobes by rotating the cams without shims in the buckets. I think he use the cams anyways but time will tell how if affects longevity.