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Message started by Red_Wine on 05/27/05 at 14:06:30

Title: Problems
Post by Red_Wine on 05/27/05 at 14:06:30

Hello all,

I ahve a 1990 400cc Savage, and have the following issues I need advise on:

a. My petc0ck's diaphragm seems to be pinched, and needs replacement, any ideas if just the diaphragm is vailable? or the petc0ck is a complete unit?

b. When the bike is idling, and if I remove the oil fill cap, I can feel burst of air coming out, does it mean I need new piston rings? and machine the cylinder?

c. I know the valve seals and guides need repair, don't worry about that.

Any help is appreciated. Thanks

RW

Title: Re: Problems
Post by bentwheel on 05/27/05 at 14:30:15

When you remove the oil fill cap it is normal to feel and hear pressure released. As far as a replacement diaphragm, I believe they are not available, but perhaps others can clarify this.

Title: Re: Problems
Post by Savage_Rob on 05/27/05 at 16:14:55

I think you could always use the Convert petc0ck to MANUAL operation ON/OFF/RES (http://suzukisavage.com/cgi-bin/YaBB.pl?board=tech;action=display;num=1113631600) procedure and not really care about a new diaphram - but not if you want to use your petc0ck like it is designed. When I look up the part anywhere, they always seem to list the entire assembly though. Personally, I'd be looking on eBay for another petc0ck assembly at a reasonable price and in the mean time, I'd either attempt to fabricate a replacement diaphram or convert the petc0ck to a standard ON/OFF/RES via the above linked procedure.

Title: Re: Problems
Post by Greg_650 on 05/27/05 at 16:31:14

The reason that you feel pulses of pressure from the oil filler is the very reason for the breather port on the top of the head cover.

When the piston moves up it displaces 650 cc of space in your combustion chamber (2/3 liter), and this causes an inrush of air into the crankcase (normally sucked in the breather). When the piston moves back down the air is again displaced and pushed back out....you don't normally see or hear any of this with the breather hose connected to the airbox.

Now just imagine what could happen if you simply plugged your breather hose (in removing the airbox for example). How would the pressures become equalized then? May seem silly once you think about it, but I know that this very thing has been done by others.

BTW - in a multi-cylinder like a parallel twin or four, all the cylinders tend to balance eachother as they are all in sort of complimentary equal positions in the rotation. In this case, a breather is more for the venting of air and water vapor than pressure.

So, don't sweat your rings on this one, unless you are belching blue smoke out the exhaust, too. 8)

Title: Re: Problems
Post by Red_Wine on 05/30/05 at 12:57:31

OK Greg,

Thanks for the reply, I understand that all that air must go somewhere, but isn't it supposed to be all displaced out the exhaust? If the piston is going up, the valves are closed, the air/fuel mix is compressed, and ignited by the spark, which pushes the piston down, right so far? 8)

Then, the piston goes back up, with the exhaust valve open and the combustion residues are pushed out thru the exhaust, right? 8)

With the inlet valve open, the piston goes down and sucks air/fuel mix into the chamber, and the cycle begins again... 8)

Now, where is that air you talk about coming from? My mechanic tried to explain it to me, but gave up after the fifth try ::)

I'll keep you posted on my discoveries...

RW

Title: Re: Problems
Post by Paladin on 05/30/05 at 13:31:55

You're talking about the upper side of the piston/cylinder. The air coming through the oil fill cap is from the lower side of the piston/crankcase.

http://savage.andruschak.net/Paladin/crankcase_venting.jpg
With a twin the amount of air inside the crankcase remains the same as it just gets shoved from under one piston to under the other piston as one moves up while the other moves down.

With a single, there is no piston going up to take the air being shoved down so it either builds up pressure inside the crankcase or gets pushed out the breather. Or out the capless oil fill.

Title: Re: Problems
Post by Red_Wine on 05/30/05 at 18:28:14

Paladin,

That explains it all, thanks.

I fully understand the situation now.

RW

Title: Re: Problems
Post by Reelthing on 05/30/05 at 19:57:47

It is something unique to a single cylinder - without another piston moving up as it moves down out puffs the air and it sucks it back in as it moves up - I've been tinkering with the idea for a couple of weeks - why not use a couple of reeds or simular(perhaps pcv's) to intake the the air through the oil fill and out through the head - seems to me this would let it run cooler - turn the back side of the piston into an air compressor.