750B valve adjusting shims uh-oh

themachine wrote:

howabout new valve seats?

Or grinding the top of the valve stem?

I have a few kz750 twin engines that will never run again. So you need shims?
How difficult is it to get them out?
michel

You could also contact this seller on ebay
eBay Link

Post edited by: steell, at: 2007/04/05 20:38

Conti wrote:

What about asking someone to grind some shims to reduce their height? A friend of mine already did that. He works in the aeronautics industry, and they've got high precision tools.
That would solve your problem, wouldn't it?

Uh, nope, fracturing a shim while cruising along at 75 mph is flat guaranteed to ruin your day.

If they were case hardened again after grinding, then they might work.

74cb750 wrote:

I have a few kz750 twin engines that will never run again. So you need shims?
How difficult is it to get them out?
michel

The easiest way to get them out is remove the cams. I looked at the link you posted and I'd be willing to bet they are not 32mm's, what he has are not listed for the 750twins.

steell wrote:

Conti wrote:

What about asking someone to grind some shims to reduce their height? A friend of mine already did that. He works in the aeronautics industry, and they've got high precision tools.
That would solve your problem, wouldn't it?

Uh, nope, fracturing a shim while cruising along at 75 mph is flat guaranteed to ruin your day.

If they were case hardened again after grinding, then they might work.

Actually, I just asked him for more details. He confirmed me that definitely works without any risk. However, you must grind only one side of the shim, and make sure that grinded side isn't the one in contact with the cam.

Hey guys! Spoke with a local machine shop that's been around for ages, they've ground many shims through the years and never had anyone come back with a complaint (ie. no broken shims). They said they could grind my 3 shims for about $20 and only one side which is to face down in the bucket. They even showed me the special highly magnetic tool that holds the shims while grinding. They can't get the 32mm size shim blanks (these are apparently odd ducks). Long story short, I'm gonna do it. I will definitely let you know the results of the grinding and if I have a breakdown (luckily I've got an extra motor, just not an 810 like what's in the bike), but these guys said they never had 1 complaint and have done alot of shim grinding. I am still concerned about the valves that have to be shimmed at 230 and 245, have to keep an eye on those as the seats or valves may be going bye-bye. Boy if this works all you guys with the 750 twins may have reason to rejoice! By the way, thanks for all the feedback!

If you really want to grind shims, you can do it just like the machine shop does, use a surface grinder with a magnetic chuck.

One of those is on my list to be added to my shop this year.

I haven't done the research yet, but I don't think it would be to difficult to make the shims, just turn down the proper material to 32mm thin cut it into disks of various thickness, harden them to the needed RC then grind them to final size.

Hmm. guess I better add a hardness tester to the list

Certainly not economically possible for me to produce them for sale, but at least I'd be able to make any size I needed.

Long live Burt Munro!! :lol:

No offense to Burt's tinkering abilities, but what of the opinion that ground shims need to be (re)hardened *after* grinding? I'm not the expert... but, I did heard the opinion voiced...

I also heard a rumor that aftermarket shims are available --unsubstantiated, as of yet--.

Klaus42 wrote:

No offense to Burt's tinkering abilities, but what of the opinion that ground shims need to be (re)hardened *after* grinding? I'm not the expert... but, I did heard the opinion voiced...

I also heard a rumor that aftermarket shims are available --unsubstantiated, as of yet--.

It appears that the 750 shims (and any shim on top of bucket) is case hardened, case hardening involves adding carbon to the surface of the metal. Since you are actually adding material to the metal being case hardened it requires grinding to return it to the specified thickness and flatness. The problem with people grinding OEM shims is that they have already been ground, so it's very possible (even likely) to grind through the surface hardening. There is a way to tell if you have ground through the hardening, but you need an RC (hardness) tester to measure the hardness at several points on the surface that was ground, and the average guy working on his own bike does not have one of those.

I am just an amateur machinist (home shop guy), but I have a friend that is a professional motorcycle machinist who is kind enough to help me out by explaining things and showing me how to do stuff that I am having problems with.

Post edited by: steell, at: 2007/04/07 09:50

It does not appear that the OEM shims have been ground to the various thicknesses needed. I tried to read up on case hardening last night and while there are different methods to accomplish case hardening, the bottom line is you are infuising carbon into the pores of soft no carbon steel while it is being heated a dull red follwed by a reheating to cherry red followed by a nice clean cool water bath. This process is done several times as each time the carbon gets deeper into the surface. Generally the case hardening goes 1mm at a minimum into the surface of the metal but is usually closer to 1.5mm. However this is apparently not an exact science and corners can be cut(also read about Ducati's trouble with their cams and other hardened parts). So the way I figure it grinding a few 100ths of a mm at most off one side of a 3mm+ shim should leave plenty of hardness. I am not an engineer or metalurgist but I do try to research and ask questions. This machine shop that will be doing the grinding for me has excellent rep and lets face it to do 3 shims for $20, they're not making any money off me either. Kawi dealer did have only 2 of the sizes I needed at $20 EACH! By the way Ducati does not make all the different thicknesses of shims for their bikes but requires the mechanic to get a machinist to grind the shims to required thickness for adjusting valves but there has not been any reports of shim failure after grinding. Man, I really appreciate all the feedback I got on this one! Great Site!!!

When you say that it looks like the OEM shims have not been ground, I'm interested in how you arrived at that conclusion.

Don't expect to see grinding marks on steel that has been finish ground to size, if you do then someone did a seriously messed up job of it. If a machine shop returned a crankshaft to you after grinding it, would you expect to see grinding marks in the rod or main bearing surfaces? Personally, I'd probably threaten to make their diet very rich in iron very quickly

Pretty much all steel bearing surfaces are ground to size, and sometimes go through a polishing process after grinding.

Hardening is a process of adding carbon to steel by heating it in, or submerging it in, a high concentration of carbon (such as Kasenit). I don't think there is any such thing as "No-carbon steel", since the definition of steel is

A generally hard, strong, durable, malleable alloy of iron and carbon, usually containing between 0.2 and 1.5 percent carbon, often with other constituents such as manganese, chromium, nickel, molybdenum, copper, tungsten, cobalt, or silicon, depending on the desired alloy properties, and widely used as a structural material.

www.thefreedictionary.com/steel



There is a good article on steel at en.wikipedia.org/wiki/Steel

By the way, my username has nothing to do with steel

Post edited by: steell, at: 2007/04/07 13:10