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Tue Dec 10, 2013 5:00 pm

Will be assembling a longblock in the coming weeks and wondering which is the best sealant to use for the piston barrels to the case. Ive seen seen people both recommend Permatex and RTV silicone sealant. The pistons I'll be assembling will also have piston shims at the case. Which one is the best to use?

Tue Dec 10, 2013 5:15 pm

I use "The Right Stuff" from Permatex It sticks like poop to a wool blanket and no leaks. I think it is a urethane based sealant not RTV and it is all we use at our shop.

brad

Tue Dec 10, 2013 5:40 pm

slalombuggy wrote: I use "The Right Stuff" from Permatex It sticks like poop to a wool blanket and no leaks. I think it is a urethane based sealant not RTV and it is all we use at our shop.

brad

X2 - the stuff is amazing and a can will last you forever. BUT its incredibly important to make sure the surfaces that you are sealing are really clean and grease free. My personal favorite degreaser is engine starting fluid.

Tue Dec 10, 2013 6:12 pm

YES, good point, spotless as you need with any sealant. I like intake air cleaner. It's very aggressive and gets everyhting out of the pores of the cylinders.

brad

Tue Dec 10, 2013 6:47 pm

I use Permatex Ultra Copper.

Tue Dec 10, 2013 7:21 pm

Dirko.

Tue Dec 10, 2013 7:23 pm

I have been using hi-temp RTV for over 20 years without a single issue

Wed Dec 11, 2013 3:01 am

I used Hondabond. First time I've ever pulled a VW engine that far apart, but so far after a couple hundred miles I've got no problems.

Wed Dec 11, 2013 9:47 am

I use Permatex Ultra-Gray and Hylomar on everything else.

Wed Dec 11, 2013 10:24 am

weatherstripping glue

Wed Dec 11, 2013 12:25 pm

I used a hi-temp RTV but only the thinnest of smears, not really as a gasket but to fill the tiny voids and scratches on the sealing surfaces. If I saw more than 1mm squeeze out at the case when I torqued it, I used too much goop.

Wed Dec 11, 2013 9:14 pm

vwpackrat wrote: Will be assembling a longblock in the coming weeks and wondering which is the best sealant to use for the piston barrels to the case. Ive seen seen people both recommend Permatex and RTV silicone sealant. The pistons I'll be assembling will also have piston shims at the case. Which one is the best to use?

"Best" is a relative term :) :wink:

After 40 years in the field, I can relate some of what I've learned and a few tips as well.

In my professional opinion, any additional sealants or gasket dressings beyond what the manufacturer has recommended is just "liquid confidence" or an "insurance policy" against leaks.
However, I also believe when you choose to modify that original design, you have taken it upon yourself to be the engineer (you must be prepared to go though testing for yourself, success or failure :P ).

That said and in your given application, I'd say it all comes down to how fast you can work for these reasons...

Tip 1) Most all RTV (Room Temperature Vulcanizing) Silicone based sealers (Ultra-Grey, Hi-temp Copper, The Right Stuff etc) skin over and cure quickly, as in 20 minutes or so. For this type to be used to best effect you should be prepared to assemble the engine quickly, that is to have both cylinders and heads on, seated and pre-torqued to 5 ft lbs within 20 minutes after you apply the sealant. For this to happen without incident you should trial fit all the parts before hand to make sure there will no issues with fit or finding all the parts needed to complete the procedure in a timely manner (if you wait too long these types of sealants can cure prematurely and act as a spacer between the case and cylinder base). If there is a real need for this type of sealant, such as porous sealing surfaces, gaps or a mis-match of parts, I would use this type of sealant and quickly do one side this way, then the other identically before finally torquing both heads to full specs in an opposing pattern.

Tip 2)If you want to work slower with less haste then you can use many of the non-hardening sealers available.
Some are age old and time tested such as Permatex I, II, Aviation liquid or paste among others. IMPO these have become messy and obsolete compared to the many modern anaerobic alternatives, which do not fully cure until squeezed tight upon final assembly. a small sample of them here...
https://www.google.com/#q=anaerobic+gasket+sealer&tbm=shop
These allow you all the time you need and if necessary to even move and shift the parts around a small amount after basic assembly.

Wed Dec 11, 2013 9:19 pm

^^^^^^^^

Agreed... I have the pistons and rings all set in the cylinders and the cylinders already marked 1-4. I also have the pushrod tubes expanded with the seals on. I'll apply the Ultra Cooper and then install the cylinder. Once the second cylinder is on i'll get the square deflector in, the pushrod tube in place and drop the head on. I then torque it to both specs.

Once done i move the other side and torque.

Fri Dec 13, 2013 7:13 am

I apply the sealant to the bottoms of the cylinders get them on and torque the heads down without messing around with P/R tubes and stuff. I let it sit for a few hours if not over night and then go back and get the tubes and deflector plates in at a leisurely pace.

brad

Fri Dec 13, 2013 7:24 am

Gotta hustle when using RTV,setup prior to assembly is important...which is why I think an engine stand is critical as well, working with the cylinders vertical is a must for seating a head quickly..

The quality RTV like ultra grey squeezes out uniformly, is highly elastic and doesn't slough off...it handles heat as well,havent had a leak using it..