hotrod Chris Craft Hercules flatty - need advice

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dave brode
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Re: hotrod Chris Craft Hercules flatty - need advice

Post by dave brode » Tue Jun 05, 2018 9:07 pm

grandsport51,

Nice looking KBL there. Whatfer valve spring pressure did you have? Where did the cam go it? Mine would be 4.75* behind, but if I jump the timing gear one, it'll be apx +3.
Dave

Keith Morganstein
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Re: hotrod Chris Craft Hercules flatty - need advice

Post by Keith Morganstein » Fri Jun 08, 2018 7:35 pm

I’ve sourced springs from the back of the SBI catalog to substitute in various flatheads and other engines. I routinely go a little heavier without issue. I figure heavier is better than lighter ( to a point).

I don’t think a flat head like that needs a lot of spring though. There is no push rod and rocker, the rpm is low and gravity is helping close the valve.

I doubt 70/140 is going to hurt a lifter that big... unless the cam and/or lifter is soft or lube is lacking. Ford flat heads use heavier springs, I seem to remember around 80/200 for performance.
Automotive Machining, cylinder head rebuilding, engine building. Old school shop, semi-retired moonlighter. Can't seem to quit #-o

grandsport51
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Re: hotrod Chris Craft Hercules flatty - need advice

Post by grandsport51 » Sat Jun 09, 2018 9:30 am

Hey Dave,
I was only called in to overhaul the flooding zenith carbs, sync them with a unisyn and Sea Trial on Lake Dora in a
'52 18' Chris Craft Riviera . Ran Great though got it to 39 mph on GPS.which i was told was decent for those boats (had been in water and was a bit heavy)
I have pretty good link for stock Herc specs clearances etc.

http://woodie.ppworks.com/references/index.html

Dave B
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dave brode
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Re: hotrod Chris Craft Hercules flatty - need advice

Post by dave brode » Sat Jun 09, 2018 12:04 pm

Gents,

Thanks for the comments/advice. I had that Woodie site bookmarked.

I remember seeing specs for a replacement spring that showed pressures that were very low. I also remember a thread somewhere in which one vendor saying that said spring was not correct, and that he had the correct "stock" springs. That said, I wonder if Hercules used light springs purposely to prevent the engines from being over-speed.

Not that I would use them, but I have tested the original 1957 stock springs and found that they are 100# per inch [34# change close to open with .340" lift at the valve] . I don't have the exact numbers here, but even stacked up tightly, 85-90 open is it. I need to check another stock engine to see what the installed height is, just for reference. I plan to break the cam in with the stock springs set light and decide on spring pressure with the honda springs later. I don't want to over-spring, but I'd like it to be safe at 4000, maybe 4200. I can't imagine it'll go more than that.

Fwiw, I realized that I made a big error when looking at advancing the cam timing from the 4.75* retard as installed. It was late at night, and I divided 360* by the cam tooth count, rather than crank tooth count. [46/23]. Advancing one tooth will result in apx +11*, not the +3.5* that I thought. I'll have to fashion an offset key, as I can't find any in 1/4" width. I suppose that I could stack two 1/8" offset keys in there, if there are 1/8" wide with 3/4" length keys out there.

Dave

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