Used Nascar cranks?

scott · 07-18-06, 08:08 PM

Anyone else tempted to buy a high dollar (Bryant...) when new... but now "used " NASCAR crank? Other than issues inherent to any used part, what would be your concerns? Anyone know what the max counterweight diameter a R302/dart/aluminum 302 blcok can accomidate?
Thanks,
Scott

Pantera1889 · 07-18-06, 10:51 PM

I bought a complete used NASCAR engine.It had been WELL used but was still the best $$ I've ever spent on an engine.

Jac Mac · 07-18-06, 11:38 PM

Im fairly sure the crank cavity is the same on both the 302/351 blocks as they both use the same crank/cam center distance and oil pan dimensions(apart from the rear main 1/2 round sealing dia).As the blocks come in raw form some material will have to be removed, but there is provision for this The only concern is if its 3.5" stroke is getting a long enough rod ratio( look into Scat chev 400/holden 308 @ 5.56/5.62 respective lengths) pm me if you need info on the piston reqd. Most people will tell you it cant be done but thats BS, It just takes a 'little' more work.

Jac Mac

Sandy · 07-19-06, 02:44 AM

Scott/Jac Mac

The motor that Keith Kraft did for my RCR has a Bryant 3.255" stroke crank in the 8.2" dart alloy block (from one of the series, cup, bush who knows). The problem was that the counterweight will not clear the stock location oil pump, and thus the motor has a dry sump. I never saw the issue, but no working around it. Not sure if this is a problem for other's but this came out a a Nascar shop acording to Keith and he didn't spot it until the engine was in final assembly...

Most of the Nascar stuff I have come across is just odd in some way, and if from ebay, like odd and either they don't know it or just won't say. Just be cautious of it unless you can get lots of details.

HTH

Sandy

Jac Mac · 07-19-06, 05:06 AM

Sandy,Scott & Ron ,

You are right Sandy, the nascar boys are up to all sorts of tricks and you need to know what you want before you buy. A lot of the cranks now run Honda size rod journals [ about 1.8"/1.9" dia from memory ] all in the interests of less mass/ drag etc. The counterweights of these cranks are undercut and profiled. The piston/rod combo to run with these has to be very light in order to be in balance which up's the $$$ factor.

To make the crank with the large front counterweight fit I plug the original 302w oilpump passage and pump attachment holes, then redrill/tap the block to accept either a 351w or 351c oil pump , both of which mount further from the crank C/L ( the 351c pump also needs the pan to be clearanced). This allows me to machine the oil pump pad for clearance. The larger pumps have additional clearance from the counterweight also. Now I enlarge the spigot bore that the dist fits in to the 351w size & get a bigger oil pump drive for free. Having done all this I tailor the depth of the oil pump gears to the requirements of the combination Im building.( I hate HV pumps & since the 351w gears are the same depth as 302w HV thats what we now have)

There is a lot of machine work reqd for rod bolt clearance etc, but by using the chev 400 or holden 308 rod you can build your 302w into a 351cu in on a 4" bore or if you use the Dart 4.125/4.200 bore you could have 375/388 cu in. Might pay to go up on the main brg size for that one though.
Rod ratio works out @ 1.59 for Ch400, 1.61 for H308. Pin height 0.840"/ 0.900".
I would not want to run these combo's @ high continous rpm for long but for the occasional track day etc they would be fun. Probably find the weak points in a porsche tranny fairly quick.All of this stuff takes time which costs if you have to get someone else to do it, but if you have the skills& desire to build a better mousetrap, why not?

Jac Mac

Russ Noble · 07-19-06, 06:50 AM

" Last edited by jac mac : Today at 08:13 PM. Reason: Attrocious spelling."

We know!! Don't bother editing you only make it worse!!

Good info, but your spelling's ATROCIOUS !!

Cheers

Jac Mac · 07-19-06, 07:41 AM

So much for your efforts not to pick on ME!!!

Cheers
Jac Mac

Jac Mac · 07-19-06, 07:42 AM

So much for your efforts not to pick on ME!!!

Cheers
Jac Mac

Tony Hunt · 07-19-06, 08:35 AM

Quote:

Originally Posted by jac mac

So much for your efforts not to pick on ME!!!
Cheers
Jac Mac

Never mind, Jac. He's been on at me for my maths!
Anally retentive schoolteacher?

scott · 07-19-06, 08:58 AM

The primary reason I ask is that I stumbled into a new-in-the-box set of Pankl rods for $400, 5.7" in length and...as was suspected above... honda journals. Any idea what might be the max stroke length a fella could reliably run in an 8.7" deck...assuming a 8.2" deck might be a tough sell.
Thanks,
Scott

Colin Artus · 07-19-06, 09:43 AM

I have run a 3.4" stroke crank / 5.7" rod in an 8.2" block (a4). The piston has a small combustion height to accomodate this with the piston pin just behind the 3rd ring. I run this combo to 7500 rpm with no problem. Those Pankl rods are the best but whether thats a reason to base an engine round them I could'nt say.

Jac Mac · 07-19-06, 05:19 PM

I dont like going below a rod ratio of 1.60 to 1 which would give you a stroke of 3.5625". On the 8.7" block this would mean a piston height of 1.22" which would be a simple build.You will probably find it easier to obtain a crank ( s/h nascar ) with a 3.500" or less stroke as the cheater crank day's are virtually gone from what I hear. However due to the reliability factor that they have now got they have many stroke options to match larger bore dia's while keeping to the 355 cu in.

Tony. What you read on here is chicken fodder, you should see the email I receive, mind you I give as good as I get!!

Jac Mac

scott · 07-22-06, 10:09 AM

Sorry for such a basic question to many but what is the generally accepted equation for determining total rod journal width required for a given rod width?

Connecting rod big end rod (doubled if 2 rods on a common journal?) + X = required crank journal width

Thanks
-Scott

Jac Mac · 07-22-06, 06:11 PM

Maximum side clearance 0.020". If using narrow Honda type rods may need to be slightly less (0.018"). Therefore 2 rod widths + 0.018" .

Any more allows the rod to 'snake' around on the journal. Too little ( below .010" ) will restrict oil flow from bearings.

GM list the factory tolerance's @ .008"/.014" for 307/350, .013"/.023" for 400.

Jac Mac

Hammer · 10-03-06, 05:29 PM

and Nascar really is a completely different ball game. they run 358 CID's BTW, the block they run can only be a dry sump.....there isn't a single oil drain back hole in the whole motor, just fittings in certain places, and the outside of the block looks completely different. Where the water jackets are around the cylinders, the block pokes out I'm assuming for more coolant capacity, and their cranks are all REALLY smooth, everything is radiused, no square edges on the whole thing, everything is rounded off. The edges of the counterweights are a smooth radius. the stuff they run is really amazing, but I would NEVER buy a used Nascar piece.........they replace all their parts before they break, now whether they are going to break the next time they turn the car on, or 2 races later, they can't afford for a motor to die at a race. but those parts are BADLY abused.....8K RPM for 500 miles w/o breaks....those motors are designed to ONLY last as long as the race and no longer, so they can run the lightest and most on the ragged edge stuff.