Sealant to replace o-rings on liners

[Srenner]

My last o-ring motor build about 5 years back used the final set of o-rings I had coerced from a major manufacturer by continually calling them and crying. This was back in the '80s before they could block my calls.

Searched JT for info on what has been used to seal the o-ring liners and find references to silicone sealants. Silicone has some drawbacks, including how thin the film can squish and still seal, so I'm looking for other options.

I seem to recall recently reading JT where someone used Loctite 518. It's a great product, which I use in several spots on the Jowett. In reading the fine print, 518 does not retain strength in a hot,wet environment, losing up to 90% of its strength. Now, I've never had 518 fail in any application where I have used it, but it does dry out over extended time. Not sure I want to risk a liner developing a leak.

Lotus V8 liners use Hylomar 3400, which is very hard to source and/or Loctite 572, also in the repair manual, although one replaced the other at some point. Lots of anecdotal stuff in various forums, but almost always using a sealant and a gasket of some form.

So, who has used what and with success?
Cheers,
Scott

[PJGD]

Scott,
On my last rebuild, for better or worse I used Hylomar. Ken Nelson has that engine now I believe but I am not aware if it has been run at all.

Many years ago, I was aware that Apple Rubber had o-rings of the right size [ID = 78 mm, X-section = 1.25 mm], but I have just phoned them and they confirmed that that size is not in stock however they can make them again but that there is a minimum order of $500.00.

Using my handy o-ring compression calculation file here, it appears that this is the right size although this is intended for conventional groove installations, not triangular shaped grooves.

Late Liner Static Crush Sea-COMPRESSION CALCULATION.pdf

[Srenner]

Lots of confusing info on Hylomar, but it appears the blue stuff come in two flavors: one with evaporating solvent and one without. The without has silica and might be an advantage as the Hylomar ages.

I'm guessing the original Jowett o-ring was round. I would think the shape it has to deform into would not matter as long as it didn't exceed the limits of the ring's elasticity. No concept of how many o-ring liner motors are out there, but if EPDM has a 20 shelf life, perhaps $500 isn't all that bad.

[Srenner]

Got to thinking of other cars using o-ring liners, called my machinist and landed on Ferrari 308 V8 motors. O-ring is 82mm x 1.21mm

DSC02284.JPG

The Jowett liner OD measures 80.98 mm. The o-ring needs just a smidge of stretch to fit over the liner and "rolls" down into place, not loose enough to simply slide, but not nearly as tight as I recall the originals. I was always anxious with the originals that I would snap one.

Alfa used o-rings on their 1300 motors with the 74mm bore, but have yet to find dimensions.

I will trial fit today, torque things down and see what tomorrow brings in the squished results.

[Srenner]

Let the fully torqued head sit 24 hrs and checked that the head-to-block gap was the unchanged, as well as checking torque on all the nuts. Nothing had changed and upon removing the head, the o-ring looked exactly the same as when installed.

I did check the liner protrusion prior to and after the head installation. With the head removed, the o-ring had pushed the liner back up to the pre-torque height. This also leads me to think that ii should be able to seal any water leaks. But, it does not verify that the liner was sitting metal-to-metal. Thinking on methods to confirm that. Might try plastigage. Suggestions welcomed.

[Keith Clements]

Engineer's blue?

[Srenner]

Right, I thought about bluing, but I'm not positive there will be witness marks as the liner just sits on the case, no rubbing or swiping. Still leaning towards plastigage, although was also considering just measuring the head-to-case clearance with and without the o-ring. Not convinced that my use of a feeler gauge will be consistent enough to discern a minute height difference. Perhaps I'm being to fanatical.

Alfa 1300cc liner 0-rings are meant for an OD of 80.45mm (Jowett 80.98mm) and are somewhere around 1.2mm, so I have ordered a set. Perhaps these with a spritz of Hylomar aerosol will seal the deal?

[Keith Clements]

A good depth vernier should be good to a thou or less. A stiff parallel bar could bridge across the cylinder.