Ok, this might be a kinda dumb question, but what are the advantages of a 1-peice rear main seal vs. a 2-peice, and whats the difference - other than the fact that one is 1 piece and the other is 2? I did try searching for this answer, but came up empty, except that the newer motors use the 1 piece, and somehow the stock roller lifters can only be used with the 1.
Thanks,
Mike

 

The one piece seal is better because it wraps around the entire end of the crankshaft. The two piece will leave a seam in two places between the top and bottom pieces of the seal. As for the roller lifters, the block design changed when the roller lifters were introduced. The lifter bores are taller to accomodate for the the roller design and at the same time the one piece seal was put into use. This is why they usually tell you that it must be a one piece seal if it has factory rollers.

 

It should be mentioned too that it's not just a matter of the seal being in 1 or two pieces. The blocks and cranks are different to accomodate the two different seal designs. It's not really a matter of which is better, it's more which do you need to fit the block and crank you've got.

 

The 2 peice seal is a mother to change with the motor still in the car . The 1 peice seal can be slip over the end of crank . The one pice get's more involed (pan & rear bearing cap have to be removed) to change . I have hear that the old block can be bored out more and that they are more durable . Any truth to this .

 

So if I was building a motor from the ground up, with all new parts, would a 1 piece be the way to go? Or does it not really matter? One's not going to seal any better or anything is it?

Thanks for the responses guys, I always like learning something new.

 

Personally, I like the one pieces better because I have had better luck with them sealing up. Also, if you are building a performance engine, a roller cam would be the way to go and they only came as a one piece seal.

 

The 1 piece does use a better seal, that is why the change was made.

Depends on what you are building, 305 and 350 where the only Gen I sbc with the 1 piece. I am assuming that we are talking sbc. You can get a stroker crank to fit these two.

Stock roller lifters came after the change of the rear seal. You may run into a 1-piece seal engine that does not have roller lifter provisions. 1986 is main year for this.

 

As of now, the new motor is still a dream for a few years down the line. I'm thinking sbc bare block 4 bolt mains (alum. would be nice but too much $$) stroker crank making it 4" bore 3.75" stroke --> 377 ci. Blower cam maybe Comp or Lunati, roots Weiand S/C (or maybe some turbos don't know yet), def. roller lifters still deciding between hydraulic or solid. I havent gotten as far as the heads or pistons/conn. rods yet, but I'm thinking somewhere around 7.5:1 compression so I can crank up the boost. Of course headers and in the perfect world w/ an unlimited budget, and time, maybe a T-56 (either stock or beefed up) or some other 6-speed. And maybe (probably) a new rear end. 2.77 just won't cut it w/ that much power, and if I do a T-56 with that nice 50% O/D, cruisin' on the highway won't be that big of a deal...even w/ some 3.73's or 4.10's.

All this when I stop being a student pilot and start being a commercial pilot...makin' the $$

 

I'LL NEVER FLY AGAIN !!!!! A third-genner behind the controls of an airplane.

 

The main reason for Chevy's change over was because of problems with the rear main seals going out. When they made the change over, the lifter bores were opened up and some bosses were added to bolt the lifter spider to. The spider holds the lifters in their bore. The other changes were to the oil pan and the rear flange of the crank. That's why you need the adapter to run a 2 piece seal on these blocks. The other really important thing worth mentioning is that the original 2 piece seal blocks were internally balanced. The new 1 piece seal blocks are externally balanced like the 400 small blocks. You can't use a 400 balancer on one of these motors though because the correct balancer has the balance weight on the inner hib of the balancer. Coincidentally, that's why you have to have a specific flywheel on the 1 piece blocks. Now that you're armed with all this info, you won't be surprised the next time the parts store guy asks what year your car is and if it's a 1 piece seal block because it requires a specific flywheel, you'll know why.

 

Lol - Yeah I get that a lot. Thanks everyone for you responses, they really helped out.

 

Factory roller cams only came in 1 piece RMS blocks, but that doesn't mean you can't put a roller into a 2 piece block.

 

It was my understanding that all 305/350's were internally balanced. My 305 (1986 in year, 1 pc rear main seal)'s balancer fit on my 350 (1974 in year) though I didnt use it because the 350's balancer seemed to work allright for it before, and I didnt want to change timing covers as well.

The flywheels/flexplates have got different places for bolts to bolt to the crankshaft, which is why you have a 2pc RMS crank and a 1pc RMS crank, flywheel/flexplate....

or atleast that's my understanding? Anyone care to clear this up?

 

The 1 piece crank doesn't have the flange on the back that the 2 piece crank does, so the flywheel needs to be weighted.

 

Thanks Apeiron and iroczracer07. You learn something new every day

 

It also doesn't mean the 1 piece RMS blocks were factory roller-cam ready. Read: 1986 blocks.

Let's pose the question a different way: You've located two 350 shortblocks, one is a 2-piece RMS and the other 1-piece RMS (and we'll say '87-later, just for grins). Both need rebuilding, and both are the same price.

As usual, there's no free lunch. Both will cost the same to rebuild, but the 1-piece, if you retain the roller cam (and why wouldn't you?), will cost more to cam. Of course, you can get a ZZ4 take-off cam from eBay and reuse your existing lifters & pushrods (but who would do that?). On the other hand, you could also re-use your existing flywheel, which you couldn't do with the 2-piece shortblock. However, the gaskets/seals will be more expensive for the 1-piece...

 

Or some truck blocks, too.

There's also relative availability. 2 piece 350 blocks are more common than dirt, while it might be harder to find a 1 piece.

Rather than worry too much about the 1-piece / 2-piece thing, find a block in good shape and use whatever parts it wants.

 

You need not have to worry about internal/external. When swapping parts just remember: 400 parts - 400 engine. No interchanging. The other Gen I sbcs: if it bolts on, the balance is fine.

If you are doing custom stuff like 383s, then know about your balance issues.

 

Ok, well I thought I was out of questions but that didn't last long.
-First of all, is everything you guys are talking about only referring to factory parts?
-Is the spider that big metal thing that bolts to the center of the valley with eight arms on it and little end pieces that cover/clip onto the lifters for each cylinder?
-If you went anywhere and searched for roller lifters, the ones that have the little bar connecting them wouldn't need a spider would they?
-Does an internally balanced crank still need a harmonic balancer, or is there some other piece that goes on the end of the crank that the pulley bolts to?
-And what is a flexplate and where does it go on the motor? I've heard of them before, but when I took apart some old 305's, all I saw was the balancer on the front, and the flywheel on the back.
Thanks, Mike

 

What specifically?

Yes

Those are retrofit roller lifters for non-factory-roller blocks. They need no dogbone retainers to keep them straight, and therefore no spider to hold down the dogbone retainers.

All engines need the dampener. Internally balanced engines use a neutrally balanced dampener, externally balanced engines use an unbalanced dampener.

The flexplate is the flywheel on an automatic. It doesn't need to have mass to store energy like a flywheel, it's just a big gear to engage the starter and mount the torque converter.

 

Specifically the bores being opened up and the bosses being added.
Is it common to find a spider being used on a motor being built from scratch from the ground up, or does it not really matter which way you go just as long as the lifters are straight and not turning?

 

That would depend on the part really. For the most part your statementis true, but when it comes to the crank, flywheel (Flexplate), dampener, and I believe the oil pan this is not true. That is really the point we're trying to make.

 

You're more than welcome. Even I find out stuff that I didn't know and believe me, it's refreshing. Especially if you were working on that particular thing and were about to screw it up,lol.

 

The bores are the same diameter, but higher. There has been an internet "kit" for converting a non-roller block to factory roller, it's been roundly hooted around here.

Somebody had a factory kit to provide the factory parts needed if you had a properly machined block. But, your engine now should have all that stuff that you could transfer over to a roller block.

Another clarification: Some 1-piece blocks, such as trucks, have everything cast for the roller provision, but none of it is machined. Doing the machining on it would probably not be worth it, because it isn't that hard to find a block that's ready to go. For the record, the 330 horse HO 350 crate engine from GM is cast and machined for rollers, but it uses flat tappet lifters/cam.

 

Comp Cams 08-1000.

 

I have a roller 1pc seal 305 shortblock. I am going to install it temporarily while I build a 350 shortblock. I wanted to use one cam and just swap it over to the 350(when its built). Should I get a roller cam or can I save more money and buy a flat tappet (what does this require?)?

305 Motor will have a 3000stall th350 behind it, rpm intake, holley 750, ported 416 heads, stock bottom end, and choice of cam (help appreciated).

 

if you go to a jy to find a roller engine, how do you know you are getting a block that is machined?

 

Take the intake off and look.

 

just look for roller lifters? type of heads on it and whether it came out of a truck doesn't matter? it will be getting a new rot. assem.,high lift vortecs,holley 750 and hei. i am looking at doing this or buying a shortblock.

i have a dead p-up that i hope to do some trading with at the junkyard.

 

It won't necessarily have roller lifters, but the bosses to mount the spider will be milled, drilled and tapped.

If you're getting a new rotating assembly, just get a block in good shape and get whichever crank you need for it.

 

thanks for the info.