TOPIC:

I have just aquired a new to me 1981 KZ750H2, and decided to do all the work on my own this time. I did a leak down test and figured out the top end needed work and that I needed piston rings on at least one piston. What I wanted to know is what do you guys use to clean the pistons and the heads. I have access to a vat for aluminum heads, but will this damage the copper valve guides in the head? I have read that it is a better idea to have a machine shop replace those, but how can you tell if you need to get them changed? I would appreciate any advice/help that anyone could give me on this matter. If you guys think I should probably opt to try and do this at a machine shop, how much do you think it would run me? These valves are really carboned up.

Go HERE and get the manual, it will tell you how to check the valve guides along with everything else.
The valve guides are either bronze or iron, I forget which.

Thanks for the tip. I haven't been able to find any direct information, and what I can seems to have been cut off by the scanner. But it has some great diagrams to follow. Anybody have any other answers to help me out?

If you can rock the valve back and forth in the guide, they should be replaced.

As for the carbon, a wire wheel bench grinder is best for the valves. For the pistons depending on how much carbon there is, full strength Simple Green may work.

Jay

From My experience in this matter you should ask you self how much cash do you want to spend if you want to do it the old farm way a quick fix to cleaning the pistons and valves some gas or vassal steel wool the rounded end of a hack saw blade work good. Use the end of the hack saw blade an lightly scrap off the heavy carbon off the head of the cylinders and pistons and face of the valves soaking the valves and pistons in the cleaner well help loosen off the carbon as you go. Once you have the heavy carbon off use the steel wool to get the lighter stuff off use a medium to light steel wool also if you can fine cooper wool or mesh to scrap with will work well and wont damage the metal. If you are using a buffing wheel use a soft wheel and let the wheel do the work don’t shave the metal off. Once you have it all clean do your measurements and make sure everything is with in its limits. Then you can decide if you need to replace guides and what not. That is my suggestion, and is what I have done for my rebuilds on my KZ 650’s.

Luc

On the edge of each valve where the valve contacts the valve seat, I would avoid using any power tools. This area is usually fairly clean. The carbon will build up on the bottom of the valve and the stem. You will find that the intake valves clean up OK with a fine wire brush on a drill or grinder as Jay suggested. The exhaust valves are usually where the deposits are burned on where they won't want to come off using a wire brush. If you have a Dremmel tool, you can use a small stone to carefully grind these deposits off. Don't hit the seat surface.

I don't know about dipping the heads to clean them. I see no reason to do this. If you remove the valves, you can get the head bead blasted if you want to clean it. Make sure you run the head through a parts washer and blow it out good with compressed air after to remove all the media.

As far as guides, I never have much luck using a bore gauge. The hole in the guides is 7mm and it is pretty hard to tell if it is perfectly round using a small bore gauge. It is easiest to just jiggle a valve stem in the hole to see if the fit is sloppy as Jay suggested. If you haven't changed guides before, keep in mind that you will also need to recut the valve seats. Although the new guide will be mostly in the same place as the old one, it will not be exact and thus, the place on the seat where the valve hits will be SLIGHTLY different and it is possible you might not get a good seat... this issue is called "concentricity" by machinists. If the head needs new guides, I suggest you get the machinst to also clean up the seats. If he does that, he may also have to do a bit of grinding on the stem ends (again, a special valve grinder is needed) to get the stem lengths within spec. The stems lengths will be a shade longer when material is removed from the seats.