Suzuki 2 Strokes

Hi Everyone,

I've just had a spare cylinder head vapour cleaned to replace the exsisting one on my GT380, as it looks a bit grubby on top of a set of newish barrels.

Thing is I didn't check it for flatness before I had it done. Now I've got it back and checked it, it's about 2mm warped across the three pots.

Do you guys think it will pull down ok if I torque the centre studs first, followed by the outer ones.
Obviously I can't have 2mm skimmed of it. Or should I just bite the bullet and get the original one cleaned.


Before.



After.

Thanks.

2mm is a lot. I doubt it would ever seat correctly. If the original one is flat, I'd get it cleaned and go with it. Otherwise, I think you're asking for trouble you don't need.

I have heard of people band sawing the heads into three seperates,
this would get most of the warp out.
but i dont know of any other probs that might arrise from doing this.
but its mo good top you as is.
cheers mark

Sawing the head into three pieces is the best thing you can do to update that design. This is because the large one piece head cannot expand evenly bolted to three separate cylinders.
Cut it carefully into the three pieces between the cylinder barrels and clean up the edges then rub each ones head gasket surface level on some glass with sandpaper.
Some people cut the centre head on a line inside of the large full length fins, doing this makes it quite narrow. I'd cut it on the outside edge of the large full length fins instead.

I am with Allan on where to cut as this will give a bit more heat exchange for the center cylinder.
Good luck, Mark

As said above, 2mm is too much warp across the three combustion chambers. I would be tempted to try cutting the head into three individual heads ... I don't think this will have any effect on running, service life or cooling (certainly not if the engine is in standard tune and with the Ramair cowl in place) and will make maintenance easier.

I'm sure I'm not the only aircooled Suzi triple owner who has cursed having to replace all 3 headgaskets every single time I needed to attend to just one cylinder.

A good friend of mine has a 550 and he had no end of issues with head gaskets leaking regardless of how correctly he torqued the nuts etc.
He runs his bike very hard and so the last time he had it apart for more gasket issues, he cut the heads apart and reports the engine has no more leaking issues at the gaskets.
Its your call, and as you have two heads you can try it out.

Agreed .... no wonder Suzuki specified in the 380 / 550 shop manual that the head nuts should be checked every 2,000 miles.

The 3 individual barrels under the one-piece head will never be a perfectly rigid structure, there will always be a little bit of movement over time, which will eventually lead to head nuts loosening and leaks.

When I rebuilt my 380, I used genuine Suzi base & head gaskets, new nuts and spring washers, and made sure all the mating surfaces were surgically clean. I check the head nuts every 1000 miles. Sure enough, the two rear nuts on the centre cylinder always need a little retorquing. Never any others, just those two.

I'm not sure why they designed it so but its definitely not the best idea. An aircooled engine with individual cylinders right next to one another is never going to have perfectly even heat distribution within the cylinder and head materials.
Having a one piece head tied to three separate cylinders with varying heating and cooling cycles means somethings got to give eventually, and in this case its the weakest point which is the joint by the gaskets.

My only concern here is that the warped head is too far gone to cure by cutting it apart. You may cut it apart to find none of the three pieces are flat. Still, you have nothing to lose by trying. Cut the warped one apart and see if you can use it. If not check the spare head for flatness, then cut it apart, then have it vapor blasted. At least that's what I would try.

Jim

It would have to be really badly warped, as in all of that issue being in some small section to not be usable after cutting. Once its been cut apart you will be able to see how each piece responds to some refinishing of the heads surface.

Thanks Guys for your replys,

Never thought of cutting it into three seperate heads and it's so obvious really

Best thing is I'm an engineering fitter by trade and work right next to a large bandsaw.

Guess whats going to work tomorrow.

gt-keith.

Ok Keith, just remember to cut on the outside of the large fins for the centre head.

Cheers Allan,

Looking at the photo's I can see that makes sense. Pity I didn't before.

I'll post some more pic's when I've done it.

My only worry is the bandsaw at work has an hydraulic vice and may damage the fins, might make up a plate slightly larger than the head so it grips that instead.

gt-keith.

OR use some hardwood blocks to lay against the cylinder head so the vise can press on that.