No base gaskets - setting squish question..

[TAftonomos]

Trying to confirm this idea (not mine)

I'm setting up my S4R now that I have new parts for it.  I might as well set squish and degree the cams while the jugs are off.

So...I've got to order HG's as they are out of stock everywhere, and cometic can make them in any thickness I need.

Instead of having to have custom base gaskets made, and using a std thickness HG, why not get rid of the BG completely, and just get a custom thickness HG made up.

if my mind is understanding this, the static CR should be unchanged, I should save a few $$ as I won't have to dick with a base gasket, AND save time putting it together as once I "glue" the cylinder down with three bond, I shouldn't have to pull it off again to install the HG (opposed to pulling everything, cleaning, new base gasket, yada yada)


Thoughts?

[ducpainter]

Will a thicker head gasket 'behave' the same with regards to expansion and seal under all conditions?

edit...

thinking about this more...if it was a good idea wouldn't it already have been done?

[greenmonster]

Wouldn`t that idea hurt squish, meaning making it bigger?

[ducpainter]

Wouldn`t that idea hurt squish, meaning making it bigger?

not necessarily.

[TAftonomos]

Remember, we are talking in dimensions of around .05mm here at the most.  Cometic has been building HG's for boost applications in the 2-3mm range for awhile now.

As far as it hurting the quench/squish....you are moving the entire assembly (cylinder/head) downward before spacing the head up.  So, if I'm thinking about it correctly, the static CR shouldn't change.

I've heard of a few people doing this before, and they all say it works.  I'll look around and see if I can find some of these base gaskets for sale (cometic wants a min order), OR perhaps I can find someone to use a lathe and shave down the jug to the correct height.

[greenmonster]

Thinkin abit more, gues you`re right.

No BG, piston & squish closer to top of comb area.
Add BG thickness to TG, all same again.

[ducpainter]

Remember, we are talking in dimensions of around .05mm here at the most.  Cometic has been building HG's for boost applications in the 2-3mm range for awhile now.

As far as it hurting the quench/squish....you are moving the entire assembly (cylinder/head) downward before spacing the head up.  So, if I'm thinking about it correctly, the static CR shouldn't change.

I've heard of a few people doing this before, and they all say it works.  I'll look around and see if I can find some of these base gaskets for sale (cometic wants a min order), OR perhaps I can find someone to use a lathe and shave down the jug to the correct height.

you might pm ducvet to see if he has a set of head gaskets...

or mail him at eric@clubhousemotorsports.com

[koko64]

I suppose getting the piston to valve clearance is the main thing and if there is room to spare up there you could achieve an increase in compression with no base gasket and the right thickness head gasket. It's one of the basic tuning mods, but requires careful measurement. Dialing in the cams may affect the clearance depending on what specs you are going for. I suppose its achieving a compression increase while maintaining a safe valve to piston clearance for a street motor.

Who's dialling the cams in for you? I would get them to adjust the squish to suit the cam timing chosen.

Are you advancing the cams at all or just getting them accurately set to standard spec and each other?

[brad black]

i've run quite a few things without base gaskets.  given both sides are aluminium, using an aluminium gasket sort of makes sense i guess.  using a steel gasket like a later desmoquattro means there's no give or pretense to what a "gasket" normally does so i can't see why it needs to be there.  theoretically everything is nice and flat anyway.

they went away from non metallic gaskets years ago (pantah days) as they would fail with revs and/or hard use.

if you can get custom head gaskets then that's one way to do it.  cometic wanted more to post them to australia than for the gaskets last time i checked (4 or 5 times from memory) so i didn't bother.  i use std head gaskets and depending on what's available i'll use a combination of std base gaskets and machine the cylinders as required (748, 916) or just machine the cylinders (996, only 0.60mm steel base available).

all you're doing is setting the piston to head clearance (squish), that's the point of doing this (some seem to not understand what the aim is).  piston to valve clearance comes after.  the static cr does change as you're reducing the clearance volume.  taking 0.4 out of a 996 is worth about 0.5 compression, 11.5 to 12:1 sort of thing.

[Speeddog]

Unless your existing base 'gaskets' are totally ravaged, you can clean and re-use.
They're really a shim, anyway, no coining to flatten out.

What's your squish at right now?

Is the Cometic standard head gasket same thickness as OEM?

Dunno whether I brought it up before, but be forewarned... the OEM oil rings are cast iron.
They're *very* *very* easy to break.

[TAftonomos]

Thanks guys for more info!

My plan is to set the squish at 1mm, degree the cams at 109/109, and run it.

I've come across these "specs" numerous times....never have heard of an instance of valve/piston interference.  I can check, but I'm not sure what the clearance is that I'm looking for.

help?

[ducpainter]

Thanks guys for more info!

My plan is to set the squish at 1mm, degree the cams at 109/109, and run it.

I've come across these "specs" numerous times....never have heard of an instance of valve/piston interference.  I can check, but I'm not sure what the clearance is that I'm looking for.

help?

After you set piston to head clearance just check the valve to piston.

[koko64]

Hows it goin' TA? Makin' progress?

[Speeddog]

Brad's got some cam timing info here:
http://www.bikeboy.org/camtime4v.html

and....

"If you run timing like I use on the injected bikes you’ll need mapping mods to get the best out of it."

[TAftonomos]

I should be picking up the head from the shop on sat...needed a valve job.  I'll spend the weekend getting the valve clearances set, assemble the jugs onto the motor w/o base gaskets, pistons in, etc.

I should have the measurements I need after that to order the HG's I need.  Then wait till they show up.

1.0 mm is the squish clearance I'm shooting for, and 109/109 on the cams.  I'll check valve/piston clearance with the stock HG/no base, and take the measurement.  Then subtract the difference from the thinner custom HG to get the clearance.  I don't have a clue what it's supposed to be, but I'm not expecting any issues as 109/109 and 1mm seems to be kind of a "standard".  I won't have a throw away custom HG to use to check it, but I can't see why this won't work.

Can't wait to ride the freaking thing!