Have you Decked the cylinder

[Matt Fisher]

Not at all a surprise since the same guy designed both of them.

Info for everyone else, I know you already are aware of it.

Make certain that the cases aren't touching the sleeve. You may need to grind a bit to make certain there's clearance. When the steel sleeve expands, it can push on the aluminum cases, causing a hot spot at the bottom of the bore. Wala- additional wear or a broken piston (right, Patrick?).

Matt I have read this twice and for some reason I am just not getting it. Do you mean the top of the cyl???

Thanks as I do not want to screw it up now

Oh and,

Just saved the cylinder before dropping it off to the machine shop today as I think I figured the squish wrong OOPS.

The orig cyl to deck was .035 + the OEM head gasket .040 total squish = .075.

The new cly to deck should be .027 (.035 -.008 w/ cometic .012 base v/s orig oem .020) + cometic head gasket .025 = .052 squish.

I was getting .020 shaved from the cylinder wow would that have been a bummer.

Now first let me that you guys agree with my math as I am getting crosseyed and second should I be decking off .010 or .012.

Also I should have this all back together on saturday and will let you know what happens.

[Claas900]

Hi,everybody....440EX4me the answer your ? about ..... "Make certain that the cases aren't touching the sleeve. You may need to grind a bit to make certain there's clearance. When the steel sleeve expands, it can push on the aluminum cases, causing a hot spot at the bottom of the bore. Wala- additional wear or a broken piston (right, Patrick?).


".....Is were the cylinder goes into the case's(bottom end) you might want to measure the roundness of the cace's.Because if it has a egg shape to it,or its to tight for the cylinder,when everthing heats's up and expands, it pushes in on the cylinder causing a tight spot for the piston,and also a hot spot(piston being to tight in the hole)...This can cause the piston to crack,so all you need to do is measure it and get like a air grinder and take out some of the material.....Hope this help's....Thank's.....

OOOH OK I get it, was just stuck thinking about the top end

thanks

[Matt Fisher]

With the base gasket on and the cylinder bolted down, the piston should be .015 in the hole. That plus the .025 head gasket will equal .040 of clearance from the piston's edge to the head.

I'd get enough shaved off to run a standard .020 base gasket and .025 head gasket. A standard fiber .020 base gasket should measure .018 after being compressed, btw. So if the piston's down .035 with a standard base gasket, then shaving .020 would bring it to .015. Add the .025 head gasket (the metal one's don't compress), and you have your .040 squish.

Then assemble everything and use a syringe to measure total combustion chamber volume and figure out your CR. If it's too high now, have the appropriate amount shaved off the top of the piston.

Fun, huh?

Well its all in there torqued down and even tested.

I ended up getting .012 shaved off the cylinder and with the cometic .012 base gasket ended up with .015(act. .010-.020) in the cyl. and everything seemed on track.

since I was working on the 400 at a friends garage and we had no syringe or other way to measure the chamber volume I thought hey why not just warm her up and put the compression tester to use.

Well sadly I must have missed something with the valves as the comp dropped to 75-78 psi. I had leak tested the valves and they held water but the exhaust originally did leak a little of the carb cleaner that my friend had tested with later. They did stop leaking after compressing the spring so I decided to have a go at it with the orig exh valves.

Anyhow the seat of the pants test was interesting. With the only mods not listed being some mild port work and cleaning up the oem headpipe the old gal performed pretty well considering all this work to lose some compression

The bottom end suffers a little bit and most likely due to the comp problem but the mid and top end somehow woke up. It did pull like never before from mid to top and this is puzzling.

I could short shift this thing constantly before and it would perform well but now it seems to want to see higher rpm for its power band. I do not mind the change and hope to get more bottom after getting the valve problem settled but does anyone have any idea why the change???????????

I am thinking the porting and opening up of the exhaust flow may be the ticket but I find I keep guessing wrong with this motor.

Also any ideas if the 479 web cam will help bring down the power band a little????????????

Thanks

[MIKE400EX]

I think maybe a valve is barely open or leaking. Those are really low numbers. Put some oil in there and see if your readings go up. Check vallve lash too. Maybe the rings havn't seated - did you check it before or after break in? Your seat of the pants improvement suggests maybe you have a faulty gage.

Mike thanks for the quick reply

Maybe the rings havn't seated - did you check it before or after break in?

Checked it right after initial break in of approx 5 min run time. I will be checking again Tuesday.

Your seat of the pants improvement suggests maybe you have a faulty gage.

I had thought this also, it is a few years old and been through some use and abuse but appears to b ok.

Will the porting etc cause this much of a change. I have never done the porting with out the cam mods before and it just seems odd.

[Matt Fisher]

I'm confused. Do you have an aftermarket cam in there right now? If so, which one?

Portwork is not going to drasticly change the powerband, unless someone really screwed it up.

Low compression will hurt low-end power more than top-end. Occasionally, you'll see guys lower the CR for full-race car motors to slightly improve the top-end, at the expense of low-end.

I would theorize that the better squish gave you more power, and you'll see even more once the compression is where it should be.