Cylinder Base Gasket Omit

[echrisconnor]

If I want to get a small compression bump out of my rebuild without modifying any components such as stretching rods, fly-cutting heads or machining cylinder bases, it looks like I can safely loose .25mm in deck height by omitting my cylinder base gaskets.

My questions:

1. CR from 8.5:1 -> 8.8:1(ish)= Worth it?
2. Sealant to use in place of gasket (Loctite, permatex...)?

Any advice would be appreciated.

chris

[Bill Verburg]

I've seen Dow Cornign 730 used in lieu of base gaskets.

[davidl]

Hello there.

Not a problem sealingwise with any good rtv.

But ifin the cyliners are not new, the ridge in the bore will surely break the top ring according to Murphy's Law.

Kind regards
david

[echrisconnor]

So david, what you're saying is that if I'm reusing my cylinders (which I expect to unless they're bad), the ridge may break the top compression ring? Is that just a Murphy's law thing, or more of a common occurrance? I've heard of folks doing all sorts of changes to deck height on used cylinders without that being an issue.

As for sealant. I've heard there is a "non hardening" sealant which is not likely to crack with age. Is the Dow in that family?

Still, is this a reasonable idea or a waste of time and effort?

[davidl]

Sorry I cannot help there..I really do not know.

I haven't done it except with as new cylinders.

And have no plan to try it and find out!

kind regards
david

[ChrisBennet]

What ridge? I've never noticed a ridge on Nikasil (sp?) cylinders but I don't get out much. The cylinders I've seen alway look like new i.e. no wear and no ridge.
-Chris

[jgparker]

I like Holimar or Curl-T on the cyliner base myself. Neither one is hardening. I hear loctite 574 is also very good.

JP

[Rot 911]

Like Chris said, I would be very surprised if you had a ridge in any of the cylinders.

[Wayne 962]

I wouldn't try this in any magnesium cases, but you have an aluminum one, so it might work okay...

-Wayne

[Porsche_monkey]

If you have a 'ridge' the seal on the cylinder won't be your biggest problem.

[echrisconnor]

Curil-t - I'll have this anyway. Will it take the heat, and is it truly non-hardening?

I've heard Loctite 574 will crack with time on the bases. Still do folks use this frequently?

Dow Corning 730. What other applications is this used for? Is it a non-hardening as well?

Thanks all.

[ChrisBennet]

Here is a discription of Curil-T and Curil-K2 I found on a VW Bus site:

Engine Sealing Products
The importance of using the proper sealing compounds when assembling your engine requires using the original compounds where ever possible. To this end, we carry Elring-Curil Products for the air and water cooled Engines.

Curil T is a Non-Hardening, Temperature Resistant Sealing Compound and forms an excellent seal where abnormally high internal pressures exist even at extreme temperatures. It is particularly suitable for sealing against mineral oils, synthetic oils, greases, diesel and motor fuels, alcoholic solvents, gases, air, water and seawater. For applications, Curil T has a synthetic base which is ideally suited for sealing combustion engines, turbo blower exhausts, turbines, generators, gearboxes, pumps and other power units as well as screwthread connections of all kinds. This is especially appropriate for sealing the square Wasserboxer Cylinder Head Seal to the Crankcase. Temperature Range of Curil T is approximately -40c to approximately +250c.

ZVC-10002 Curil T 75ml Tube $xx.xx


--------------------------------------------------------------------------------

Curil K2 is a Non-Hardening Sealing Compound which can be applied with an excellent sealing effect on assemblies which require minimum torque loss and where high surface adhesion is required. Components with groove surfaces can be sealed efficiently and will remain functional under conditions of mechanical, chemical and thermal stress. The components can be easily dismantled. Curil K2 can be applied with a brush with the optional hand-pump that screws to the tin can it comes in. It insures great effectiveness in the sealing of internal combustion engines, gearboxes, pumps and other power units and particularly at disconnecting points such as cylinder head base gaskets, gearhousing gaskets and screwthread connections of all kinds. This is especially appropriate for engine crankcase halves, cylinder base, alternator/generator tower and fuel pump mounting base. Also for the Cylinder Head Nuts on the Wasserboxer where they have to be sealed when torqued on. Temperature Range of Curil K2 is approximately -40c to approximately +200c.

Gotta love a sealant that is bright green...
-Chris

[echrisconnor]

That's a pretty good, clear product description. Curil K2 is recommended for base gaskets, howeve T seems very similar. Any reason not to use T?

Thanks Chris!

Nobody has said I'm a crack-head for leaving the base gaskets out, so I intend to go for it. Wayne's comment that it "might work OK..." I take with the usual degree of caution. I read that as "You can very likely get away with it with no problems, but there's a gasket there for a reason. Don't come bi#chin if it leaks down the road." Is that fair?

[Porsche_monkey]

Why not dial indicate the surfaces or check them on a layout table. The more deviation from perfectly flat the more you need a compliant gasket. Lots of engine components do necessarily need a a gasket, the gasket just allows wider (therefore cheaper) manufacturing tolerances.

[Wayne 962]

Originally posted by echrisconnor
Wayne's comment that it "might work OK..." I take with the usual degree of caution. I read that as "You can very likely get away with it with no problems, but there's a gasket there for a reason. Don't come bi#chin if it leaks down the road." Is that fair?

Am I that obvious?

-Wayne

[echrisconnor]

Those of us who have read enough of your posts have started to build our own "Wayne Translators."

[911pcars]

Hey Chris,
Here's another path you could take.
Check each cylinder height, then trim as necessary up to 0.0098" (.25mm) max (your dimension) so each is the same, then use the .25mm base gasket and favorite sealer. It'd be even better if the case spigot surfaces were also machined. That way, you ensure all the cylinder assemblies and top end are evenly clamped and parallel to the crank and to reduce the chance of oil leaks at that location.

Sherwood

[ChrisBennet]

Originally posted by echrisconnor
Nobody has said I'm a crack-head for leaving the base gaskets out, ...

You're right, that's not the reason we're calling you a crack-head.

Just teasin' ya.

Looking at the problem, we're dealing with a smooth surface subject to light oil pressure on a seam that moves some with contraction and expansion directly over a a pretty hot exhaust.

In my ignorance, my concerns would be with sealant squeazing into the case and whether the gasket serves another function such as keeping the cylinder and case from hammering each other i.e keeping fretting from occuring. The latter is probably not a valid concern because the 964 doesn't have a base gasket there.

If it was me, I would have the case decked just enough to square everything up and use some base gaskets. The extra compression you get is not going to make big power.

-Chris (fellow crackhead)

[echrisconnor]

Sherwood,

Machining .25mm off the cylinder bases was going to be my original approach. I'd heard of people frequently running with no base gaskets for the same effect without machining and the associated cost. My question really was "Is omitting the cylinder base gaskets an acceptable approach (and if so, what sealants work)?"

[jgparker]

Curl-T has an amazing ability to stop oil leaks, so you should do very well with no gasket. I hear it can even stop a Triumph/Norton/Jaguar/MG (Insert favorite English vehicle here) from leaking...

JP