Cyl base sealing

[OldTee]

A Excellence Magazine (Dec 2003, pg 42) Technical Notes answer to a question about sealing a 2.0L engine got the following response.

" You can probably get by with just using the copper gaskets with the small bores of the 2.0 liter engine. As the engines got larger the bores got bigger we had a lot of trouble with the copper gaskets slipping out fro under the cylinders or getting beaten out. What we prefer -- if the clearances allow for it -- is just leaving the copper gaskets out and using Dow Corning RTV 730 to seal the clyinders to the crankcase. If you find that you do need the copper washers to provide adequate clearance between the pistons and the heads and valves, you might want to put a thin bead of Dow Corning RTV 730 on each side of the copper gasket."

Dempsey mentions nothing about sealants on cyl base gaskets.

So.

[Henry Schmidt]

RTV is a lame option for this application.
For cylinder base gaskets we only use Curil "T". Curil "T" is a high temp non hardening sealant that is one of only a few sealants that are certified for use in nuclear reactors. This fact alone gives us extreme confidence in this product.
A thin coat on both sides of the gasket and you're good to go.

We have found that for most applications on air cooled engines RTV is lacking in anything like durability and internal beading resulting in oil worms is totally unacceptable in quality engine overhauls.

RTV works well to seal water cooled engine applications like water pump and water manifold issue.
Remember this mess still leaked. RTV is evil.

[304065]

I would not leave the gaskets out unless you have the cylinders machined to reduce their height by 0.25mm, otherwise you will end up with a piston that is too close to the head, or expressed another way, too little deck height. I plan to use them in my 2,0 and use Curil-T.

[Henry Schmidt]

Originally posted by john_cramer
I would not leave the gaskets out unless you have the cylinders machined to reduce their height by 0.25mm, otherwise you will end up with too much deck height. I plan to use them in my 2,0 and use Curil-T.

Hi John
I think you got your statement reversed.
By removing the base gasket you reduce the deck height.
The taller the cylinder the greater the deck height.
Deck height equals cylinder height plus base gasket minus piston height.

BG+CH-PH=DH

This assume that piston height is meassured from case spigot.

[304065]

Henry, of course you are right: "More" deck height means a numerically greater measurement between the cylinder sealing surface and the deck of the piston, whereas "less" is a reduced measurement. I was thinking "taller piston top relative to where you measure" but used the wrong word.

Just so somebody following the bread crumbs doesn't take the wrong path, I have edited the response above.

We now return you to the regularly scheduled engine rebuilding forum.

[bob barnes]

Henry,

You might want to do a little investigating on the RTV730. It is not like your normal RTV. Woods introduced this product to me when I had a fuel cell leak once. It stopped the leak! It also cost $80.00 for a 3oz tube which should alert you to the fact that it's different.
I suggest you read the Dow Corning label/fact sheet. You might be enlightened. I just purchased another tube for my Race Engine sealing.

Bob

[Henry Schmidt]

Originally posted by bob barnes
Henry,

You might want to do a little investigating on the RTV730. It is not like your normal RTV. Woods introduced this product to me when I had a fuel cell leak once. It stopped the leak! It also cost $80.00 for a 3oz tube which should alert you to the fact that it's different.
I suggest you read the Dow Corning label/fact sheet. You might be enlightened. I just purchased another tube for my Race Engine sealing.

Bob

Bob
Your post has an interesting tone and enlightened is an interesting term.
Generally research before spewing drivel is recommended.


# Limitations as listed by Dow http://www.skygeek.com/rtv730-3oz.html

Dow Corning 730 Solvent Resistant Sealant is not recommended:

# For continuous underwater immersion where adhesion or structural bonding is required
# On concrete, brick, mortar or other masonry surfaces
# On surfaces to be painted; paints do not adhere well to sealant (paint before applying sealant)
# On materials such as impregnated woods or oil-based caulks that bleed oils
# In totally confined areas; atmospheric moisture is required for cure on Teflon1-coated materials, polyethylene, polypropylene or methylmethacrylate Plexiglas2); sealant will not adhere well
# On or near sensitive metals such as copper, brass, zinc, carbon steel, galvanized iron or magnesium; these metals may be corroded, especially in confined cure conditions, due to the acetic acid released during the cure
# With solvents such as acetone or ketones

The last time I checked base gaskets were made of copper, biral cylinders are made with carbon steel and Porsche cases and ancillary parts from 1968-1977 were made from magnesium.
We choose products bases on their compatibility with all Porsche engine components.
Thanks for the lesson. Feel free to offer advise whenever you feel like jumping in.

[bob barnes]

Henry,

Thanks for your reply on what Dow says the RTV730 can't do! How about stating what it can do! You could have also shown that it's purpose stated on their Web as well as printed on this box in front of me: RESISTANT TO MANY FUELS, OILS, & SOLVENTS AND (-70DEG F TO 500DEG F). I have also sealed a leak on the gas tank of my son's '67 Cougar with this RTV730.I would think that this is more important than worrying about corrosion of the small copper base gasket.

Bruce Anderson and Jerry Woods have been using this product to seal the 911 early Magnesium race cases for years with neglible effect on these cases. I have one of these cases built in 1998 by Woods with the RTV730 and it didn't leak-it's now apart and there is ZERO corrosion! It cleans better than the Loctite equivalent and did not leak a bit! Very important on the Race track if you are running a Porsche in SCCA and don't want to get Black-flagged by oil dripping or blowing on a header.


Bob

[Henry Schmidt]

Originally posted by bob barnes
...............................I would think that this is more important than worrying about corrosion of the small copper base gasket............................................ ...

The title of this thread is Cylinder base sealing.
Dow 730 looks like a great product for sealing gas tanks, although I would generally choose a better repair.
The next time a question about a half a** fuel tank repair arises, I'll remember this posting.

The problem with RTV in general is that it beads on both sides of the material you are sealing (squeeze out). That bead can break loose (with as little as 15 psi according to Dow) and travel through the engine clogging vital oiling holes.
That's a risk I'm not willing to take when products that doesn't pose that risk are available. Loyalty to habits are understandable but progress is quite often measured in small steps.
It's your engine , you get to choose.

[bob barnes]

Henry,

Every engine builder has to assume some risk in his attempt to deliver a product to his customer or in my case an engine that doesn't leak oil. RTV730 could present some issues if the user was not careful in applying it. Likewise, if one chooses to torque the ARP bolts versus using the stretch method.

Applying a small bead around the middle of the cylinder base and using your vinyl clothed finger to spread the bead and let it sit for about ten minutes before you insert the cylinder should prevent any fallout of 730 into the engine, but it will seal the cylinder in the case as well as seal the copper base gasket to the cylinder and case.

Preparation and attention to detail in using this product will make this a must have on any serious 911 engine rebuild either for street or Race application-at least in the Jerry Wood's training camp enough said.

Bob

[Turbo_pro]

Bob, you may be lecturing the wrong guy about attention to detail.
There are a number of great engine builders out there but no one is building a sweeter motor than Supertec.

Do a search and you'll see what I mean.

[bob barnes]

Jim,

Henry's end products look pretty!

The comment was for those who want to seal their cylinders with the RTV730 which was mentioned in the Excellence Mag. It is obvious that the author of the article and Henry have different opinions. I did not read the article but I know that in Northern ca. the product is highly recommended. I know of the issues that Henry is concerned if the 730 clogs any oil passages or spray bars. If you read my reply, I've told how I put the 730 on to help ensure that the 730 stays on the intended parts and seal the cylinder to prevent oil leaks as well as not fall off into the engine.

Bob

[OldTee]

At $95 for 90ML at Ellsworth Adhesives (other places may be less expensive) is this really worth it for a single (at least at the moment) 911 OH? The spec is quite good.
I can understand why this, or any, product would not be used during original manufactur, but the changes and wear occasioned by 100K miles can use some help. In fact, the damage from leaking oil under the cylinder bases is not such a good thing, I think.

Spec:
RTV-730 Features
Potting
Mold Making
Rollers
Pink
Initial mixed viscosity: 15,000 cps
Specific gravity: 1.1
Hardness shore A: 30
Tensile, Die B: 750 psi
Elongation: 400 %
Tear, Die B: 115 ppi
Linear shrinkage: 0.1 %
Thermal conductivity, (BTU·in)/ft (2) ·°F): 1.1
Coefficient of thermal expansion, cm.cm °C: 29x10 (-5)
Typical Temperature Resistance, °C: -54 to 204
Dielectric Strength, V/mil: 460
Dielectric Constant @ 1000Hz: 3.0
Dissipation Factor @ 1000Hz: 0.004
Volume Resistivity, ohm·cm: 7x10 (14)

[Eagledriver]

Old Tee,

I was a firm believer of using the Anerobic Locktite products on cases and cam towers because that's what the factory used. One of my racing buddys that I taught to rebuild his engine insisted on using the 730 RTV because Jerry Woods shop uses it. I couldn't be happier with the 730 RTV. I have since used it on my engine when I rebuilt it. I think it does a great job and to me is easier to control how much to use and where the stuff gets squeezed out than the Locktite. It seems to have a different feel when cured than the normal silicon rubber.

It is expensive and so I wouldn't buy it for cylinder base application. I would use a non curing sealant like Curil T or non hardening black permatex (I use this). I also don't like the idea of using a hardening sealant on the base gaskets because it takes hours to get the top end assembled and torque the headstuds. This causes the sealant to cure (even 730 RTV) before the cylinders are fully seated.

-Andy

[bob barnes]

Andy,

Stromski Racing sells some cylinder hold downs that can be used to ensure the 730 is squeezed to its minimum on the base gasket, sealing the cylinder to case and allows the heads to go on at a later date. Two per cylinder would be reccommended. I've never had a oil leak in this area in nine years. As you know, you purchased the tube in hand because the main purpose was the case sealing operation and cam tower to heads. I would hestitate to spend the money just for the cylinder.

Bob