Hey twinners,

I'm planning to modify one of my heads to accept a larger piston dome, but before I begin I'd like to get some practice on a junk head. If you have something with cracks, damage, etc... Let me know. Will cover shipping, and a little cash for your effort. If you like, I'll remove the valves, springs, keepers, etc and send them back when I'm done.

I think I have one, I'll check this weekend.

-Jessie

I have one gasket surfaces are in good shape. Gotta see if it will fit in a flat rate box to ship to CA. It's one that you could actually use if you were to do whatever it is you're doing correctly. No cracks/warping, just 1 bent valve left that I haven't removed. I take it you don't want the camshafts/buckets?

Jessie, if you have one that would be awesome.

How's the valve seat on the head with the bent valve? If the seat is okay, it might be possible to just replace the valve, and/or guide. I'd hate to ruin a usable head.

I have a good head with one or more bent valves, left over from my rebuild. I was probably just going to throw it away. PM me if you are interested.

Okay I'm a noob at this stuff but larger pistons = bigger displacement right?

Does that mean you'll have to change the carbs/spark plugs to accomodate it too?

Jared gave me 2 cylinder heads but I must have taken them to my Bedford house.  I'll be up there April 15th if you are not in a hurry.

-Jessie

Rayshon - depending on how much larger the pistons are, there may be a need for new carbs. Usually not the so much the plugs.

If it's any help, I believe I have a GS450 head laying around.

Did anyone give you head yet? Did you get a head job?
I have a couple spare really good heads to rebuild 2 1989 engines. I can take a head of of one of the bad 89 engines I was going to rebuild. Let me know if interested.

Quote from: rayshon on March 25, 2012, 01:40:32 PM
Okay I'm a noob at this stuff but larger pistons = bigger displacement right?

Does that mean you'll have to change the carbs/spark plugs to accomodate it too?

All other factors being equal, larger pistons = bigger displacement. Displacement is a combination of the bore (piston size,) stroke (how far the piston moves) and number of cylinders. You can calculate this out:

Pi * radius of the piston squared, times the bore in mm * number of cylinders = total displacement of the engine.

In the case of the stock GS500:

(3.14159 * 36.5 ^ 2) * 56.6 = 236892.6935065 * 2 = 473785.387013 square mm = 473cc

It's rare, but there are situations where you would increase the size of the piston and reduce the stroke... Or even eliminate one of the pistons.

In this case however, I'm installing a piston with a larger dome. This doesn't mean that I'm installing a bigger piston, just one with a different shape. That often means higher compression, which produces more power.

(Technically, I'm installing a smaller piston with a larger bore... I'm doing it because of race rules.)

Re-jetting isn't a bad thing... It's part of making more power. There are a number of engine mods that don't affect jetting, and a number of very mild mods that don't require re-jetting... But almost anything that makes big improvements to power will benefit from adjusting the jets. It's not that hard to perform the work... The real hard part is figuring out what adjustments will work best.

No one's PMmed me for shipping details yet. I'd love to get a used base and head gasket in the package in order to take some measurements as well.

I'm in no rush. I have some major stuff going on right now, so It'll probably be at least a month before I can get started.

I looked on the boxes I received. Weight for a head was 25 pounds. Weight of jugs was 15 pounds. We can calculate shipping from that.
The two 1989 engines I have are supposed to have bad compression. I was planning on just replacing the jugs, pistons and heads. I haven't turned over the engines yet or measured compression.  Does that sound like the easiest plan for the engines?

I can pull a top and jugs if that's what you want for experimenting. I'd like to keep the shims because I don't have many extra shims.