when you have a lobe failure in a flat tappet bbc its not something you're going to have to check the lash to know its there. it'll be denoted by the loud hammering sound, and a miss. usually when a flat tappet wears and everything is working properly the wear is VERY minimal suprisingly. the problem with the bbc is the lifter bores are rarely where they're supposed to be in a production block. this is fine if you run the laziest ramps on earth (that reads stock or close to it for agressiveness). the normal force and such has very little to do with the wear up to a point. basicly the way a flat tappet works is, you have a hemispherical foot with maybe a .001" or .002" crown on it. and you have a .001 or so taper from one side of the lobe to the other. this serves two purposes one it keeps the cam walked back into the motor so theres no need for a cam button like with a roller. and the second purpose is to make the contact between the lobe and lifter offset from the lifter centerline which creates a torque and spins the lifter and pushrod etc etc. its a common misconception that flat tappets are grinding along the lobe. when in actuallity they're spinning acrossed it. i'm unsure if you were aware of any of this, but there it is for what its worth. now you're depending on some very slight variations to keep things working properly, and trusting a 20 year old production block to have things in the right place?

and again i must emphasize that i do not think that you have 10.2 compression. at the very least get something and peak in the spark plug hole with a piston at top dead center. you should be able to identify a substantial dome, somewhere over 27cc's + the valve reliefe volumes. it is extremely difficult to achieve much compression with open chamber castings and anything less than 500cid, without a really big dome. i just say this because even a big chevy can be a stone with a big cam and no compression. and i wouldnt trust those stamped rockers as far as i could throw them in a 6000rpm plus app. not trying to be a pain in your ***, but i've been down these path's before just like i'm sure a few of these other fellas have too.

 

Not to be a pain in your *** either but I have to agree with the other guys here that you have to look at the long term and what is really the better value.

Check this out(NUMBER 43) http://www.rehermorrison.com/techTalk/


The $640 solution to making a flat tappet with solid roller lobes live on the street.

http://www.schubeckracing.com/new2/i...position=61:53

 

Good links

 

after reading this whole post one thing comes to mind.

You thought of a different or cheaper hobbie

 

Most of the time I like to learn from others, but this is something I have to learn for myself.

WS6T3RROR, yep I knew about the spinning lifters, and I'll check the combustion volume before I buy any parts. Just FYI, it's a 1987 LS6 crate motor.

captaindbol, those Schubecks are SICK! They make me want to forget about roller cams completely.................. almost.


So, what is the pressure limit for flat tappet cams with non-Schubeck lifters?

 

I guess since your commited to the idea and your taking a poll(gamble) on the future of your engine, I would also recomend the COMP 11-679-5. Reason being it is a tight lash cam with modern lobe profiles that stand a better chance of living in a driver. Comp beehive springs 26120 would be a perfect with 155# on the nose. I would splurge on a good set of roller rockers and not worry about binding the stockers,since you can use them down the road with any future upgrades. Make sure you get a good oil pump and forget about restrictors and deal with any parasitic windage losses.

 

Thank you, captain! I'm glad someone is willing to help me within the limits of my insane mind.
Two questions:
1. "Modern lobe profiles" usually means more aggressive (right?). Why is that better than gentle Crane lobes in terms of not destroying the cam?
2. Why is a tight-lash cam better than a standard-lash cam? Tight lash cams can't take much variation in lash, so you can't really run lash loops on them like you can with a regular lash cam. That was something I was looking forward to doing.


My comments on this being a gamble:
Yup, the whole engine is a gamble: stock rods with knurled-shank bolts, unknown rod bearing clearances, old rings, factory balance, etc. Basically, not tearing the whole engine down and inspecting/massaging/replacing/refurbishing everything is a gamble. I'm going to cc the combustion volume to verify CR, take a main cap off and look at the bearing, plastigauge it, and go from there.
If I plastigauge one of the rods, that means the stock bolt will be tightened another 2 times, and that's a BIG gamble IMO. So I should replace the bolts. Well, that means resizing the big ends. So while they're out, I might as well polish them and have them balanced. But that means the pistons have to come off, and a few might crack, so I might as well have the small ends bushed for floating pins and get better pistons, but then again it's not really worth it to hop up the stock rods, so I should get new rods, but then they'd be spinning on a 1053 forged cross-drilled crank, so I should get a new 4130 nontwist forged crank, and I might as well throw on the Dart heads, which means I really should get a roller cam and shaft rockers... Holy smokes, I've replaced everything but the block! No reason to use a piece-of-crap lousy-oiling factory block, so I really ought to get a CNC Bowtie block. The snowball is now as big as Cincinatti, and is rolling at 131mph.
(Yes, a little of that was sarcasm and hyperbole.)

So basically it's all or nothing. I definitely can't afford all, so I'm choosing a tiny bit rather than nothing. Someday, more than 10 days after I graduated from college and once I have a decent-paying full-time job, I'll build an all-out killer big block. But that day is not today.

 

Yep, and it's a expensive lesson. How much money you willing to spend to "learn" this lesson?

BTW Captanbol gave you some great advice and you ingored it.... the springs are half the battle... problem is the 155lbs on the seat might be a bit much to break in a flat tappet with traditional lifters and 1.7:1 rockers.

Bret

 

What did I ignore? The Comp 11-679-5 tight-lash cam with modern lobe profiles, beehive springs, roller rockers, good oil pump, no restrictors, dealing with windage losses...? Just because I didn't comment on something doesn't mean I ignored it.
I figure I'll break in my cam with the old, weak, worn-out springs. Maybe just the old outer springs, depending on what they test out at.

WS6T3RROR, and anybody else who's interested in crate LS6 compression, I cc'd my combustion space today. Turned the engine to TDC according to the balancer and timing tab, rotated the engine on the stand so the plugs were pointing up, and filled the cylinder with a 50/50 solvent/oil solution. 100cc filled the cylinder and the bottom 2 threads of the spark plug hole. BBC guys will note that the spark plug hole is not quite the highest point in the chamber, so I'll admit I missed a few ccs there. But then you also have to figure that the piston probably wasn't exactly at TDC, and that probably took a cc or two extra.
100cc combustion space figures to 10.30:1 compression. Then if we add 3cc for the space not able to be filled through the spark plug hole, we get 10.03:1.
From my experiment, guesstimations, and the specs I have read, I'm comfortable saying this is a 10:1 motor and that the factory spec probably is 10.2:1 like I thought.
The pistons have TRW embossed on the underside, so they might be p/n L2349F, which are listed as a 29.4cc dome closed chamber LS6 454 piston.

 

Just out of curiosity, what oil did you use, and when was it?

 

i used a straight wieght valvoline oil, 40 i think. its probably been a two years now since i had that problem. i also used gm eos, and a bottle of comps break in lube which is simmilar to the gm stuff. if either of those products help i cant say but i've put dozens of cams in small blocks using them and havent had any failures there yet (knock on wood).

 

Sounds like you did everything pretty much like I would have. This is why I asked:
Not too many years ago, all regular solid lifters were being made by just three companies. When one of them went belly-up, the other two had to sacrifice quality for volume. Many oil companies also drastically reduced the amount of zinc dialkyldithiophosphate (ZDDP) in their oils due to pressure from the OEMs because they thought ZDDP was degrading their catalytic converters. ZDDP is an anti-wear additive that is especially effective for flat-tappet cams (GM EOS is basically a 40-weight oil carrier with alot of ZDDP in it). So these two factors wiped out alot of flat-tappet cams that would have been fine with good lifters, oil with a reasonable amount of ZDDP, and a pint of GM EOS for good measure.

Just thought you guys might like to know, if you didn't already.

 

yeah i was aware of that, thats why i initially started using the eos.... however all of my failures have pretty much been found to be geometry related due to the stock blocks. when you start pushing the limits of what a flat tappet can do everything has to line up or you'll kill it every time. in all of my cases i would eat one lobe and after a couple of times replacing the cam and lifters to have the same lobe wiped out again (checked lifter/bore clearance and it was fine every time), i learned my lesson and i use rollers almost exclusively now in big blocks. if the customer cant hack it i tell him to come back when he can. i really dislike doing a job twice especially when it usually entails engine removal and disassembly.

 

Yet you didn't tell the guy who seems to be dead-set on running a flat-tappet cam. What's up with that?