hotrod Chris Craft Hercules flatty - need advice

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dave brode
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hotrod Chris Craft Hercules flatty - need advice

Post by dave brode » Fri Jul 12, 2013 4:29 pm

Hello All,

Helping friends with a nice ole wood '56 CC 20' Sportsman. Fairly rare boat [most were 17"], 3rd owners, all paperwork. Rebuilt engine, but original to boat, 3 & 7/16" x 4 & 1/4" [237"] flathead Hercules KLC 6, rated by Herc for 120 horse at 3800, 180 lbs-ft at 3000. We bought some spare parts, which include a '57 131 horse engine, said to be the same, except two updraft carbs, 131h at 3800, 192t at 2800. As is, it'll pull hard enough to get to 3200 on the stock tach with 3 aboard. The plan is to mothball the original engine and "hotrod" the dual carb'd engine. It would be a shame to blow the original up.

The horse peak is 3800, torque rating at 2800. I figured that it would have big rod journals that would allow an offset grind, but not so, they rod journals are 1.988", and real wide [apx 1.1875" BEW]. The rods are apx 7" long, and have what I call a pinch bolt end at the piston. The pistons are split skirt stuff, although just 3 rings. I haven't measure C.H yet. Scary looking stuff. They do have 7 mains, at least. One other issue is, the copper Victor head gaskets aren't much larger than the std bore. I'll have to look at other brands. Rods/pistons aside, the ports don't look too bad, at least compared to a ford flatty. Combustion chamber over the valves, which aren't terribly puny. Have to stay with the updraft Zeniths [cast iron!], due to engine cover clearance. The 120 horser acts like it has some overlap, it has some lope, unlike the lower horse K family engines, which idle smoothly. The flywheel on the 120 and 131s is lighter than on std Ks, might be able to lighten it up some more.

I was looking at 7" flathead rods. There are aftermarket I beams with 2" big ends, but their BEW is way thinner. Some slant six mopares have a 7" rods, and a 1.200" BEW, but their journal is 2.187". l'll look to see what they are doing for offset grinds. A custom set of pistons would not be beyond the budget, but a welded stroker may be.


Anyone have advice, or source for long rods with a 2" or smaller journal size?

Thanks in advance.
Dave
p.s. - I thought that I could adapt a modern harmonic "balancer". There is no dampner

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by Dan Timberlake » Fri Jul 12, 2013 5:55 pm

How much power or speed improvement are you looking for?
If the factory HP rating is correct, and it won't pull to max hp rpm I think it has the wrong prop.
Last edited by Dan Timberlake on Fri Jul 12, 2013 5:56 pm, edited 1 time in total.

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by Tuner » Fri Jul 12, 2013 5:56 pm

A heavy flywheel gives a boat more stability because of the gyroscopic force. Of course, it affects acceleration but it has no effect on top speed. The difference between a sheet metal auto trans wheel and a 30 lb. wheel in a V-drive flatbottom is profound, significantly more stability in rough water.

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by PackardV8 » Fri Jul 12, 2013 6:37 pm

There's no horsepower in rods. Change them if you want, but why? The Hercs don't like to rev, so there's no power up there where rods might be a problem.

Verify your compression and figure how much milling to get it to 7.5 - 8:1 compression and run premium fuel. Sonic test the combustion chamber roof thickness and relieve it following the KR750 H-D pattern. Somewhere from forty years ago, I have the design cross-sections. Maybe someone here (Panic ??) might have them digitally stored.

If cost were no object, I'd have Jones make up a billet cam with his best guess high intensity flathead profile. With some decent springs, you can run an almost square nose on those and add a bunch of area under the curve for more power at a sane livable RPM.

You've already discovered, Hercules parts are some of the most expensive out there. $100 each for a stock cast piston, $400 for main bearings.

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by dave brode » Fri Jul 12, 2013 8:04 pm

Dan,Tuner, & Jack,

Dan, I'm no boat guy, but I thiought the stocker ran pretty well for what it was....How much does he want? Good question. Perhaps a small rebore, some add'l compression and porting is logical. Assuming there some metal there, a large overbore would be nice, the gasket issue aside.

Tuner, I will re-think the further lightening of the flywheel. I could attach a modern dampner on the exposed flywheel, which faces forward in the boat. I got on that kick due to reading adding them on Ford flatheads.


Mr. Vines, On the rods, I realize that there's not power there, it's just that the rods and pistons both scare me, even at 3200. I'd hate for it to chuck one. Pistons too. I realize that it isn't going to spin 5000, but thought that some better rods and modern pistons were good ideas. The subject of the chamber roofs and flow around the valves and along the roof caught my eye last night during some web searches. I'll study that subject further. It didn't make me feel good about the fact that I moved the chamber roof toward the valves about .120" on my "hotrod" 8 horse Techuseh snowblower engine. It looks like I'll be studying the science of flat head porting.

Yes, the stock hard parts are pricey. $100 for a copper head gasket. $500 ish for a set of good rods didn't seem like a bad idea. I'll ponder the cam option.

Thanks fellows.

Dave

p.s. - I'll put a wheel on it and see what the cam looks like
Last edited by dave brode on Fri Jul 12, 2013 8:35 pm, edited 1 time in total.

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by dave brode » Fri Jul 12, 2013 8:32 pm


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Re: hotrod Chris Craft Hercules flatty - need advice

Post by PackardV8 » Fri Jul 12, 2013 8:40 pm

FWIW, I've never seen a Hercules truck or boat rod break. Modern pistons, yes, but the Herc piston has so much compression height above the pin that most manufacturers don't have a forging tall enough.

Those H-D heads are exactly what I was looking for. That and the cam are where most bang for the buck can be found.

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by Tuner » Fri Jul 12, 2013 9:45 pm

I think Iskenderian is who to talk to about flathead engine cams.

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by dave brode » Fri Jul 12, 2013 10:11 pm

Tuner wrote:I think Iskenderian is who to talk to about flathead engine cams.
Isky 404 with radiused tappets :mrgreen:

Just kidding, don't want to go there.

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by crazyman » Fri Jul 12, 2013 10:17 pm

If money wasnt as big an issue, I'd think that a 9" or so rod with a short piston with a modern ring package would be the ticket.. Maybe a custom rod with off the shelf pistons..

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by dave brode » Fri Jul 12, 2013 10:23 pm

I don't have the KL [long stroke] all the way apart yet, but have some pistons from a std K, which are apx 1.750" C.H. I'm assuming the KL will be .060" ish shorter yet [4.25 vs 4.125" stroke]

Fwiw, I saw some parts from a larger ML engine, 4 rings, extra scraper below the wrist pin. Makes these K/KL parts look like vega engine parts

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by vincenelson » Sat Jul 13, 2013 10:01 am

I did a 1954 metro a few years ago and I started out by going to Venolia and had them build me a custom piston set for it. I wanted to get a better ring package than what was stock. I am sure that if you call GRP they will make any size aluminum rod size you want. If you need your crank shaft worked on I and sure that Henery Valasco of Valasco cranks can help you if you sweet talk him a little. The venolia pistons that I had made cost less than the stock metro pistons, and had a modern three ring moly pacakage. Good luck on your boat.

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by Keith Morganstein » Sat Jul 13, 2013 7:54 pm

A supercharger would be a good option. A low mounted centrifugal sized for low - modest boost in the stock rpm range seems ideal.

Jones Cam Designs will regrind a cam for you. He'll do that oddball stuff and it will work.
http://www.jonescams.com/2006catalog_005.htm

I'll defer to Jack Vines on Herc rod strength. BUT if you want rods....

Jeff at Murphy's Motor service will make you custom billet 4340 rods. He has a nice design, pretty much any size. Not inexpensive at all, but a good value for what you get. You may have to wait a bit until he's "making rods" to get yours. He has a modest CNC shop and they switch over to rods a few times a year.
Jeff made a custom size version of the "Farmall 560 rod" design for me. http://www.murphysmotorservice.com/rods.htm

One thing about the very long rod (solution for less comp height) in the not so big bore. you may have interference at bottom of the bores. Best to mock it up, with shop fabricated mock up rod.

PS> I don't like welded/welded stroked marine cranks. (Tractor pull, they're ok).
Automotive Machining, cylinder head rebuilding, engine building. Old school shop, semi-retired moonlighter. Can't seem to quit #-o

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by dave brode » Sun Jul 14, 2013 1:13 am

Vince, thanks for the info, Although this guy is pretty much a start it up, back out and go wide open. Alum rods don't like that, afaik.

Keith, Dang, now those are some long rods! You think there might be enough lobe for a regrind? Some boost does keep popping into mind. I imagine 4-5 psi would make a huge difference.

Thanks to all who have commented so far. I'll try to get the cam degreed in the 4.25" stroke engine, and get it apart this week, check piston C.H. and so on.

Stupid question of the week. Main bearing spacers are commonly used. Anyone seen them used in a rod? I ask because there are affordable H beams sold for slant sixes. 7.005" long, BEW is ok, but they are for a 2.18785" journal [herc has 1.988"]

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Re: hotrod Chris Craft Hercules flatty - need advice

Post by PackardV8 » Sun Jul 14, 2013 1:28 am

In theory, a flathead boat engine should really love a turbocharger. Plumbing's on the same side, RPM range spread is low, the prop acts like a high-stall converter to allow boost to build and hold,
thus helping overcome the inherent breathing problem and it all happens within the safe operating RPM.
Stupid question of the week. Main bearing spacers are commonly used. Anyone seen them used in a rod? I ask because there are affordable H beams sold for slant sixes. 7.005" long, BEW is ok, but they are for a 2.18785" journal [herc has 1.988"]
Once again with the rods. Just what is it about the Hercules rods that has you wanting to replace them?

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