Offset Grinding 292 Inline 6 Crank

[pdq67]

Harry,

You might want to look over a 250" 6-banger P/U engine that has a 1-piece head on it. '70's/ '80's or so engines??

The stock dual exhaust manifolds are way cool to me. As is the 2-barrel carb intake flange!

BUT the I-piece heads tend to crack so really suck! Most guys ran the old P/U's until the 1-piece head cracked and then threw it away and put a regular 3-piece head on.

pdq67

[strokersix]

Harry, I clearanced my crank counterweights round in the lathe as far as I could then set up to mill them the rest of the way by rolling the crank about the crankpins under the milling cutter. Actually clearanced for 5.7 rods used in a previous build. (5.7 rods, 383 sbc 4 inch pistons). That build ran ok but showed some peculiar witness marks in the cylinders. Current build with 6.0 rods and .060 overbore the cylinder walls look great, no problem.

I can't say whether the sbc Streetdampr is right or wrong. I guessed. I can say that I don't have a broken crank and have no trouble with flywheel bolts coming loose so I think encouraging. And I'm not afraid to drive it hard.

If you put 292 crank in 250 block watch out for rod clearance to the camshaft. Most cams have clearance notches cast in. If you want to use the mechanical fuel pump you will also need to do something for rod clearance at the pump lobe. I reduced the lobe diameter and relieved the connecting rod to allow this. Easier is electric pump.

[enigma57]

Thanks, strokersix. That's pretty much what I thought dropping a 292 crank into a short deck 250 block would entail. I will probably end up using a tall deck 292 block, but was curious as to how you might make the long stroke crank work in the short deck 250 block.

FWIW...... I was thinking that a destroked 292 style crank might allow the inline 6 to be spun up a bit higher than the stock 4.12". Was thinking a square engine with 3.875" stroke would do it and could be fit into the 250 block, as well. I contacted a guy who can build a forged 4340 crank for these engines for around $2 grand each. Expensive, but worth it in my view. Only catch is...... He would need to make a minimum run of 5 identical cranks or more, and being retired, I don't have $10 grand to invest in the project, then selling off the ones I couldn't make use of.

How did you deal with the narrower big end of the 6" long small block V8 rods?

When running a V8 torsional dampner, since the balancer ring does not have V-grooves, I thought about running an early sbc (short pump) bolt-on crank pulley and making a spacer for the water pump pulley to space it out so it will line up with the crank pulley. Then rework any accessory brackets to align with the crank and water pump pulley as well. Is that how you did yours?

I had Isky grind my cam on a 292 core. If I were to drop it into a 250 block, the fuel pump location would not be an issue, as I will be running an electric fuel pump. I hate PCV valves on carburetted engines, so plan on making a plate that bolts to the unused fuel pump pad and adapting an old 216 or 235 baffle and road draught tube there for crank case ventilation. Will run breathers on valve cover, as well.

Thanks,

Harry

[enigma57]

Harry,

You might want to look over a 250" 6-banger P/U engine that has a 1-piece head on it. '70's/ '80's or so engines??

The stock dual exhaust manifolds are way cool to me. As is the 2-barrel carb intake flange!

BUT the I-piece heads tend to crack so really suck! Most guys ran the old P/U's until the 1-piece head cracked and then threw it away and put a regular 3-piece head on.

pdq67

Thanks, pdq! I have 90% of the pieces to complete my 3-carb intake setup and I have a set of Langdon's split dual exhaust manifolds which I modified to accept 2-1/2" exhaust. Just need to clean up the brazed areas a bit and drill/tap them for 3/8-16 studs to cinch up exhaust pipes, then coat them.

I did look at one of the 250 1-piece heads out of curiosity. But it would be impossible to access quite a few of the areas where I need to do some hand porting and fit the lump ports. Might be able to have one of those heads extrude honed if you had the bucks (I don't), but I doubt you could rework one to flow anywhere near as well as the older style head having separate manifolds.

As far as that goes...... When I first thought of building a later model inline 6 for my '57...... My first thought was to build up one of the 230 or 250 OHC Pontiac Sprint engines. Had a buddy who had one in a '67 Lemans in the late '60s. I had never seen anything rev that fast nor high at the time and it would smoke the tires and move that heavy car like a good running V8. Hard to believe it was a 6 banger under the hood. As I recall, he drove the heck out of it and had to change cams and cam followers several times each year, though.

I thought about building an OHC Pontiac 6 with one of the 244 degree 'H' cams along with the same reworked Weber intake and larger dia. split exhaust manifolds I will be using on my Chevy inline 6. But the cost and the lack of parts availability now of days for the OHC engines made me decide otherwise. I even thought about dropping a 292 long stroke crank into an OHC 6, but they need to rev to make power and if you're not going to rev them...... Why bother with the hassle and added expense of building an OHC 6?

Best regards,

Harry

[enigma57]

Well, I think you know the what you want.........Good......The dual engine Triumph made a few passes at Maine the summer before last..It ran near 150 MPH but had a random flooding issue on one carb than cut speed.Front engine lost oil pressure due to failed seal that wasn't supposed to fail.I was not there to fix it....No damage but he parked it and set a few records on the single engine bike...I fixed the problems but since then the bike has been on display in his bar...Every year is supposed to be Bonneville but it's a 5000 mile round trip and no one wants to drive that far...

Tony, maybe the guy who set your dual engine bike on display rather than riding it on the salt isn't driven in the same way as was Burt Munro....... "If you don't follow through on your dreams, you might as well be a vegetable."...... "You live more in five minutes on a bike like this going flat out than some people live in a lifetime."

Choosing to display the bike rather than ride it reminds me of the crusty old cowboy Jack Palance played in 'City Slickers'. There is a scene near the end of the movie where Curly tells about a beautiful woman he admired from afar, but he never told her. When asked why he never pursued her, he said something to the effect that he'd been with lots of women and the real thing could never be as good as he dreamed it, so he chose to keep dreaming rather than face the probability that a relationship with her in real life wouldn't turn out the picture perfect way he would want it to be.

Best regards,

Harry

[strokersix]

Harry, I destroked mine from 4.12 to 4.062 while crankpins from 2.1 down to 2.0. This keeps most of the material in the overlap between main and crankpins, buys a bit of clearance, and a bit of rod angularity. Well, I don't have a crank grinder so I did have to outsource that work and balance. Thankfully the balance was close and did not require any special effort.

For rods I have run stock inline chevy, stock OHC pontiac, and currently running shelf Crower 6.0 made for the 250 inline. So I've not had to do anything about big end width.

I shortened the SBC damper hub to tuck it in close. Probably counterbore the crank gear next time. Pulleys and brackets are salvage from parts pile, cut, modify and fab from scratch.

I have eyeballed the 292 crank in a Pontiac OHC block. Looked like a drop in but I did not actually try to assemble so can't say for sure.

[chevyfreak]

I'm a big admirer of the chevy inline 6 and have 2 x 230's, 3 x 250's where the one i'm currently building going with a 4 inch bore.

Anyway, my friend is building one where he took a 250 block opened to a 4" bore and a 292 crank to make 311cubic inch. Crank was turned down on big ends to use 250 rods and using a 292 cam and only place he had issues with clearance was with piston skirts touching on counterweights with the std 5.7 rod.
Pistons were clearanced and soon to go for balancing on the whole assembly.
He is using the big 292 damper with 3 belt grooves and Weigh is almost same as a 8 inch sbc damper.

Chevyfreak.

[enigma57]

Thanks, strokersix and chevyfreak! Much to consider. Will be back in touch soon.

As an aside...... I was told many years ago when building engines, to use the best parts I could find (which in those days were forged pistons, rods and crankshaft), to balance the bejavvers out of it and set redline RPMs not to exceed 4,000 ft. per minute for sustained engine speeds.

292 harmonics issues notwithstanding...... For the Chevy inline 6...... 4,000 ft./min. piston speed equates to......

292 (4.12" stroke) - 5,825 RPMs
250 (3.53" stroke) - 6,800 RPMs
194/230 (3.25" stroke - 7,385 RPMs
3.875" stroke (custom crank I'd like to do) - 6,195 RPMs

For short runs under 15 seconds down a dragstrip, you can probably get away with spinning the engine faster, but for sustained high speed running (circle track or road racing, for example) to stay under 4,000 ft./sec. piston speed as a rule of thumb.

Best regards,

Harry

[strokersix]

I think the 3.875 stroke and 6.0 rods would be a sweet spot! Keep in touch on your progress please. I am interested in a crank like that. And I know someone else who might be as well.

[enigma57]

Will do, strokersix. I believe it would be a great combination as well. A square engine (3.875" bore X 3.875" stroke) with 0.040" overbore comes in at nearly 280 cu. in. and I believe such a combo would be perfect for a 230 or 250 short deck block. Still need custom pistons with 1.2125" comp. height if I did the math correctly (9.15" deck height?).

I went back and dug through my e-mails just now. I contacted Tom at Molnar Tech. with this idea in Feb. of 2018. I asked for a ballpark quote on a fully counterweighted 4340 forged crank and he said the factory would do a minimum of 5 cranks per run, all having same stroke and each crank would be around $2,300. He said he'd need to do it in billet, as there are no new forgings available for the inline Chevy 6 in this stroke and he'd need a stock crank to get dimensions from. As with all such things, I am sure there would be a significant lead time involved, but did not touch on that, as I didn't have the money to do 5 cranks. I did ask his recommendations on a torsional dampner and he said he preferred ATI.

OK...... Just got off the phone with Tom Lowe. Ran both ideas past him (long stroke billet 292 crank and destroked 3.875" billet crank). He likes the 3.875" stroke crank with 6" rods in short deck 230 or 250 block the best. Should be a sweet running combo. He won't throw in with us for a run of billet cranks, as he has so much inventory at present, but he has a working relationship with Molnar and would act as a facilitator if needed.

If you would like to get together and have Molnar do a run of 5 or more 3.875" stroke billet cranks and know some other guys who would be interested as well, count me in for 1 crank. Pretty sure this will be a cash up front deal with a long production wait, so put it that way to anyone who may be interested.

Best regards,

Harry

[strokersix]

Harry, sent you a PM

[COMP461]

I have been a part of playing with maximum effert Inline6 engines. I would check with a few people like Kevin and Glen Self. They might have some parts laying around that might work in what your doing. I beleive I might know where the raw cranks we got from Chevy might still be boxed up. A good crank shop could do what ever you want out of a good crank core. We also recieved a number of casting that had no water jacket , ports or chambers. They weighed almost 300 lbs I'll look for those cranks next week. here are some cool pictures of that project and heads.

[strokersix]

I am drooling over that cylinder head. Thanks for the images!

[COMP461]

The motor we ran this head on turned 10,000 and made 675 hp out of 265 inches on gasoline

[enigma57]

Sweet! That 12-port head is a thing of beauty! Doing this on a budget, but if you have any of the unfinished cranks or other parts that I can incorporate into my build, I'm definitely interested. We're up the road a piece from Houston near Spring. You are up around the Dallas / Ft. Worth area then?

Best regards,

Harry