The Stovebolt Site Forums The Shop Area Engine Shop installing neoprene main seal

Should the ends line up at the cap/block joint line, or should the ends be offset say, 1/8 or so? Will it make any difference?

Also, a dab of gray or black (since that's what I have) RTV at the ends?

Didn't see any guidance on the Best Gasket website, so asking here at the center of the universe of Stovebolt Knowledge.

Most folks offset them just a wee bit...maybe a couple of mm or so. You shouldn't need any RTV at the ends, but they say to use non-hardening gasket sealer where the seal fits into the cap & block groove. I'm sure you've already handled this part but the mating surface on the crank needs to be polished very well. If it is pitted from the use of a rope seal (and they will be) then the neoprene seal will last only a brief time before it loses its lip. The best thing may be to add a Speedi-Sleeve on your crankshaft's end (the mating surface). If you do that, add some red Threadlocker and you can consider leaving the lip so that it will act as a slinger after you hammer the Speedi-Sleeve in place. You'll see 2 grooves in your end cap. If the lip on the Speedi-Sleeve is left so that it fits right next to the back side of the inner groove (but doesn't touch it), then oil leaving the rear bearing will run straight back and will be slung up into the first groove (so you'll have less there to make its way to the seal). Now having said what I said about offsetting the 2 pieces, around 2000 I talked to a fellow at Fel-Pro who was retiring. He was one of their engineers and impressed me as a pretty smart man. He said they had stopped suggesting people offset the seal pieces...that their research showed it was of minimal benefit and that the seal was designed so that end pressure would form a fine seal without offsetting the two pieces. He added it provided some confusion which the company wanted to avoid. Apparently some folks had decided if a bit of offset was good a whole lot of offset was better so they were trying to rotate the two pieces around the surface so the ends sat opposed vertically...which was causing trouble. So, who knows? Anyhow good luck with it.

Oh, one other comment. When doing this I always take a piece of paper about 1 inch wide by 8 inches long...cheap copy paper which is usually about .004" thick...and set it so that once the rear main cap is installed and tightened (you needn't torque it yet) there will be notable resistance when that little strip of paper is pulled out the back end. If you don't feel resistance, then remove the crank and both seal pieces and using self-adhesive foil tape make yourself some strips that you can apply to the bottom of the channel the seal pieces fit into --- to shim the seal pieces closer to the crank. Check resistance at top and sides.

Jon, a shim like that tightens the seal twice as much at the parting line as at the top and bottom. I guess that's all right since the seal lip is flexible, but it's why adjusting bearing clearance is done with a tapered shim- - - -twice as thick in the middle than at the ends.
Jerry

Jerry, doesn't that geometry apply only if you shim just one half of the seal piece (or bearing half)? I mean if you wrap a piece of .002" thick shim stock all the way around the circumference of say a crankshaft journal and mike it, you'll now have a total of .004" less no matter which 2 diametrical points you choose to measure. Top, bottom, parting sides, wherever you choose, the reduction will be identical as long as the shim is applied equally all around the journal.

If you used a tapered shim (let's say .004" tapering to .002") under both the top and bottom bearing half, the centers of both bearing halves would be pushed in by .008" whereas each side would only be pushed in by a total of .004". Right?

Tapered shims were used more frequently back when engines got an "in the frame" ring job about every 30K miles or so. The common practice was to adjust the bearing clearance by shimming behind only the bearing shell in the rod or main cap, not all the way around. The tapered shims allowed excessive clearance to be taken up by moving half the bearing closer to the crankshaft by reducing the radius. There's more to the process than meets the eye, such as filing a little off the ends of the bearing shell to retain the proper "crush" on the bearing.
Jerry

Semi-related question: which is preferred…the Best Gasket rope or the Best Gasket rubber?

They are not interchangeable. An engine designed for a rope seal cannot use a rubber seal, no matter who makes it. The depth of the grooves are different. Either one can be machined for the right fix- - - -a full circle lip seal.
Jerry

Hmm...pretty sure my 235 was designed for a rope seal. I'll re-read the factory manual to see if there's a reference to a rubber seal. I'll default to Jerry's knowledge in any case, but did order the Best neoprene that seems to fit great in what I thought was a rope seal groove (pics in first post). This 235 doesn't appear to have had any other work done since new.

Probably rope. Rubber didn't gain popularity until the mid 60s or later.

Best makes a rubber seal for Cadillac 429 that they claim is interchangeable with a rope seal. They start leaking 60 seconds after cranking the engine.

That's 30 seconds longer than it takes a rope seal to leak!

The neoprene rear seal was made for 1956 (and later) 235 engines. Not to say rope seals were not still in use during those years. They were but in 1956 the grooves were machined more precisely and prior to that, they weren't. Actually I've seen some 235s into which small pegs were set (into the grooves) presumably to keep the rope seal from moving with rotation of the crankshaft (image attached). There were 6 or 7 little pegs set into holes which had been drilled in this one. The neoprene seals were commonly installed by dealerships or repair shops hoping to stop complaints...often without doing anything to the surface of the crankshaft. You can see the surface of one crankshaft where originally a rope seal was used and later a neoprene seal was installed...and you can see the neoprene seal removed from that same engine and the roughly 1.5mm missing from the lip where the crank had ground it down nicely.

The groove above (with no pegs in it) is simply to show the difference between the two...even though today seeing the two side by side is a bit confusing.

Best Gasket lists both a rope and a rubber rear main seal for 1954-62 truck 235. How does one tell my looking at the groove…which to use?

Skooter, you mentioned a 1952 pickup and if you have the 1952 235 you'd be right...it wasn't designed for the neoprene seal. Doesn't mean you can't use one. You can do that but you may have to shim underneath it to ensure it makes a good seal with the surface on the crank. Or likewise I suppose the groove might have been machined in a fashion where it is too shallow and might press the neoprene seal too firmly against the crank (though I've never seen that yet). Seeing you may have a 1952 235 is why I came back and added that idea in my earlier post. By far the best way to handle this is to machine the block to accept a one-piece seal (like the one used on the harmonic balancer). Jerry has built a jig to allow that to be done, but you have to have or have access to a Van Norman (or similar) boring bar. Good luck!

I don't think there is an answer to that question...at least not one I know. I've saved some caps to compare over the years and honestly I haven't been able to discern much difference (aside from the odd one with the pegs that had been set into it). If you want to use the neoprene replacement, first of all I'd look for an NOS Fel-Pro gasket on eBay. They created this seal and maybe Best Gasket is a wonderful operation but I think of this like I think of voltage regulators. There are the right ones and then there are all the imitators. I don't like re-doing rear seals, so I want to trust Fel-Pro in this case. If you put one in (sans gasket sealer) just check the fit as I mentioned with a piece of common copy paper by snugging up the rear bearing cap. If the engine is in the truck, check the top first and then the bottom and the sides. The crank will be sitting as low as it can be due to weight, gravity, etc so the top clearance will be the key. It is also important (as common sense should tell you) the closer to .001" clearance between your journal and bearing you have the better things will be back there. Good luck!

My 235 is a late '55 version, which if the main bearings are any indication might fall into the '56 range. At least it seems to. Following thread closely and very much appreciate the info.

If you have the later type bearing inserts, I'd agree it argues yours may be more like the 56...but in all honesty the topic of the neoprene seal is not treated on the GM Heritage Pages and reading Chevy shop manuals (all the ones I have) there's no mention in them, either. If anyone has something official, I'd appreciate seeing it. Every single thing I've heard about this seal (for over 50 years) is 100% heresay from mechanics, dealership parts people, folks on internet forums, etc. I have some very good info from GM dated 1957. Not a single word about this type of seal is in there.

Someone around here (maybe 52Carl?) thinks the Best Gasket rope is the cat’s pajamas.

Concensus seems to be it's the only rope seal that's worth using. I have a Best rope seal in the package, and also the Best neoprene which I'd planned on using but could change my mind pending more study of this thread and others.

I can confirm Jon G’s statement. My ‘59 235 came with a rope seal installed and I replaced it with a neoprene seal.

I have in in my head that most of the “in the truck” main seal replacements I’ve read about here…have involved the rope seal.

Can the neoprene seal be installed “in the truck” as well?

It might be worth a try, but would be the opposite of pulling the top half through with a sneaky pete tool. The neoprene is two stiff semi-circle pieces. You'd have to push the top half through, starting underneath the crank and rotating it up and over. Would likely require alot of lube...and that's the very condition that might make the whole thing spin after installation (not good!).

Maybe there'd be a way to pull it over with a sneaky pete type rig, I dunno. There's no good way to do it in the truck, and seems there's only one good way out of the truck, and that involves machining cap and block for a one piece seal.

Thinking further, (and that's all this is...the imagination of a rookie noob engine builder, so be careful following my advice!!) if you could lower the crank maybe 1/4 or 3/8 inch you could set the top neoprene half on top of the crank exactly in line with the seal groove, then raise crank and seal into the channel just right.

It could be done. Worth a try, IMO.

Both rope and neoprene Best seals come in a sealed envelope, so if you have both on hand you could probably sell the unopened one you don't use here in the swap meet section.

You will find the reference to the neoprene seal in the 1956 passenger car shop manual supplement. That seal was introduced for the passenger car line, along with the 848 head. Late 55 block? You have to be careful There are late 55 blocks for the end of the 55 model year and there are 56 blocks cast late in 55 for the 56 model year. Those early 56 blocks used neoprene seals. Truck blocks may be a different animal. Pontiac blocks used the neoprene seal.

Yes it can. To remove one, disassemble a windshield wiper blade and remove the thin polished stainless steel piece that acts as a stiffener. Bevel one end and remember to insert this so the bevel faces the old neoprene seal and not the bottom of the slot. Lower the crank (2~2.5mm)...remove transmission, harmonic balancer (once it is removed you can lower the crank a bit without damaging that seal), oil pan and loosen all main bearing bolts to let the crank drop a bit...some will also remove connecting rod nuts and push the pistons up and out of the way. Once you push or lightly tap this piece through, the old seal will come loose...if it doesn't, grab the exiting end with needle nosed pliers and tug it toward you. To install one, Skooter is on the right track. First draw a piece of t-shirt wet with naphtha or mineral spirits through to clean the groove as much as possible. Then apply non-hardening gasket sealer to the new seal (just a thin layer), guide it over the crank and lift the crank by tightening the bolts (except for the rear main cap, that is) a bit as you guide it in.

However...important note: if your crankshaft sealing area is pitted and damaged from an old rope seal the neoprene seal won't work well nor very long. In that case you'll need to remove the crank and install a Speedi-Sleeve over the sealing area just like you need to do for the harmonic balancer shaft.

Another comment: If you have a rope rear main seal which is leaking, I've seen people use the windshield wiper stiffening piece as a fix. Trim for length using the lower main bearing cap. Lower the crank a bit and drive this piece through the channel on the back side of the rope piece (leaving the rope seal in place), which forces it outward by the thickness of that stainless steel piece (usually these are something like .015" thick or so). Then replace the rope seal on the lower bearing half and tighten all up again.

Interesting. I assume we’re talking about the “old style” blades have the exposed metal suspension?

And on the wiper blade fix of a rope seal…would one be doing that only on the block side? Or also the cap side?

Yes, the old Trico or Anco type blades (some of which are still made today) that have the two stainless stiffener pieces on each side of the rubber part. These slid into the four pairs of 7mm "claws" and locked at one end. I saved probably 6 or 8 of those for things like this. Not that you couldn't use a common piece of K & S stainless, but it might be too wide and also the ones in the wiper blades were spring stainless. Just the block side is all I ever saw being done. Really easy to replace the rope seal in the cap piece. I tried it once on a 1956 Cadillac and it did indeed stop the leaking. Pain in the bottom to pull the pan on that thing but the leak was pretty bad.

Maybe like this blade:

https://tinyurl.com/4jmks3u8

Would it be advisable to use a spring steel backer on a new rope installation? Suspect the added pressure might cause accelerated wear on crank surface but now is the time to ask, while engine's upside down on the stand.

Currently leaning toward the neoprene and gonna get back on it soon (after finishing some unrelated stuff).

No, I don't think so. Usually that is done to try to make the upper seal fit tighter against the crank surface...after a problem is already in play. The whole plan is to do something (anything) to help stop the leaking without taking that upper rope seal out. Replacing that upper seal with a new one while the engine is in place and not having it leak doesn't always happen.

If I were in your shoes and my engine was upside down on the stand I'd remove the crankshaft and install a Speedi-Sleeve on the rear crank surface (with some red threadlocker) and then I'd use the neoprene seal. I think the part number was 99386 but you ought to check me on that. You want the sealing surface of the crank to be as smooth as possible. Whether the Best Gasket seal is okay I can't say, however.

Speedi Sleeve does or does not require machining? Points well taken on surface pits. Did very close and careful inspection of crank, and yes after hitting it with crocus cloth there are still very miniscule pits right in line with where the neoprene sealing edge would line up. Probably not visible in the pics.

So went ahead and opened the Best rope package and what do you know??...there's instruction for drilling the cap groove for a 1/16 roll pin, which is included, intended to keep rope from spinning. (Says to use Ultra RTV in applications where drilling isn't advisable.)

So at this moment I'm leaning toward the Best rope because of much wider sealing area, versus the thin edge of the neoprene is sure to make the "microscopic" pitting worse over time.

A speedi-sleeve needs no machining. It just drives in place over the end of the crankshaft, with a dab of red loktite to seal it to the crank surface. I used one on my balancer to help the timing cover seal.

Has anyone ever considered adding an oil slinger to a stovebolt crankshaft flange, just inboard of the seal area? It wouldn't be very difficult to do while the crank is out of the engine for machining. I'm thinking of a 2-piece disc attached with small machine screws to the front of the flange.
Jerry

The Speedi-Sleeve only requires trimming for length and removal of the lip (if needed), Skooter. It comes with a metal cup you would use to drive it on to the crankshaft and then once it is on far enough you would trim the end length to match the surface of the crankshaft. It is a very thin stainless steel sleeve. I can see some pitting, etc on your crank, so I'd say that might not be ideal for the neoprene seal...although yours is better than many I've seen. And at this point I should add I want that crank surface to be as smooth as possible regardless of the type of seal used...but with the rope seal the Speedi-Sleeve might reduce the clearance too much...might crowd that type of seal. With the Speedi-Sleeve there is a lip that will be contacted by the metal cup (to facilitate driving it on). It sticks up about 1/4". That lip can be removed (there is a place scored on to the sleeve which shows where it would normally be separated) or in the case of the 235 that flange could be left in place and allowed to ride in the inside machined slot (rounded top) you see in either of the images above. If you left that lip in place it would act as an oil slinger. In the 235 the oil coming back to the rear main seal isn't under pressure, but the spot where it leaves the rear main bearing is so close to the flange of the crank that oil naturally runs freely to the area. Slinging oil up and into that second machined slot has always seemed to me what GM should have done in the first place, but you know...they never asked me about this. You need some oil to keep any seal from burning but given the slope of the 235, there will be some oil there no matter what. But in theory you could run that lip to within about .009" or .010" of the inside of that second machined slot...that being probably the most end play your crankshaft would have. That should cause a lot of the oil to slow down and be forced through the opening at the bottom of the rear main cap.

Very interesting about the instructions for the roll pin. I didn't know that, but then I haven't bought a rope seal of any type in over 40 years. I did post some images of a rear cap I saved where somebody had placed 6 or 7 little pins to keep the rope from shifting. Any movement of the rope isn't going to be good.

I have decided the most important thing is to have as little clearance between the rear main bearing and the rear crank journal as is possible...and .001" should be ideal. That will at least limit the amount of bouncing up and down the crank can do and the amount of oil that can squirt out.

Anyone have part numbers for Speedi Sleeve for 235 crank seal and harmonic balancer? Must've seen it in another thread, can't find in this one.

Yes, I mentioned this in conjunction with use of the Speedi-Sleeve a few months ago, Jerry. You can only drive the Speedi-Sleeve on in one direction and if you don't separate the lip, you automatically have a slinger. It could be placed within .009" or so away from the inside edge of the inner channel (so that it wouldn't rub...9 thousands being as much end play as your crank should have).

Check me on this but I believe it is part number 99386 for the crank. The harmonic balancer sleeves are all over the place out there...

Here's the info on that Speedi-Sleeve: Link
Measure the crank diameter and length to be sure it fits.

I bought my harmonic balancer one from RockAuto. But they don't list the rear main sleeve.

I don’t have a crank Speedi-Sleeve in front of me to look at. And perhaps I’m not fully understanding “where” exactly you envision the sleeve flange ending up.

But I have installed Speedi sleeves in other applications. Would we not be concerned about the paper thin flange coming loose and doing naughty things inside the crankcase?