As usual Jimbo is right. I have a ton of flathead cranks even a couple of the induction hardened ones. But I am building a stroker and using the Chrome molly billet crank from ARC.The Part number is 495645 but they are no longer available from Briggs.
I'd suggest the ARC billet crank. Part number 6580
think you may have answer the magical myth how strong the flathead 5hp crank is. 2 season and no problems with the crank. seems to be a lot of put down on the stock crank. alot of 'maybe's' it can't do this or that...etc.. but no real hard evidence that it's a big problem to run.Ive got a small block animal with a flathead crank in it, super stout piece, no problems with it and have ran it 2 seasons... other than it tends to want to push a lot of oil out into the overflow, last time i ran it, it pushed the oil seal out on the flywheel side...is that because of the shape of the lobes of the stock crank and shape of the inside of the case affecting the circulation of the oil and approx 8000 rpms, or something else? . Btw- the motor has 2 vents on the side cover and 2 vents on the valve cover...
yes I agree too if a person was to build a 3inch bore and run a billet head,big cam ...etc methanol gas then your asking for it.Oh man there are so many variables.
How much HP, what RPM you are running it at, how hard the clutch hits and since there are no new cranks anymore how old is the one you are installing and how much clearance do the bearings have.
I haven't used a cast crank for a long time because they scare the hell out of me. I also don't use the 6580C because i haven't found them to be any better than the cast briggs crank.
If you build a 2.690" bore a good low mileage Briggs crank will probably last but if you are building a 3" bore or bigger with a good head and carb and want to spin it at 9K I'd suggest you don't put that thing on a minibike unless you want to get a job as a unich.
mine has had some head port work done with bigger valves/dual springs with an alky tilly on it, I don't dare go that big with the bore/piston....mind you, I run mine on mainly small ovals with tight corners.....and lastly, no, I do not have the budget....yes I agree too if a person was to build a 3inch bore and run a billet head,big cam ...etc methanol gas then your asking for it.
5hp crank in a animal block with a small bore and a stock animal head and just spinning only 8000 rpm's...it's just going for the ride.
didn't think of the pvc valve...ive got the vent tank vented with the size tubing/fittings as the incoming line...not at all familiar with the "pin punch the side cover" thing....The why of it must be pressure . The outlet on the vent tank has to flow more then the lines that connect too it .
You could pin punch the side cover , thats a 50 / 50 fix .
Loctite stud and bearing seal .
A pvc valve on the vent tank might help as its drawing in as much as its pushing out . Add in cylinder pressue. It might be quite a bit .
It would be interesting to connect a manometer to one of the vent lines .
Because i mentioned ive run a mod animal with flathead crank in it that ive had no problems other than it pushes alot of oil out to the overflow tank, and mist recently, it pushed the oil seal out on the flywheel side of the engine case....were trying to diagnose it and looking for possible solutions to keep it from happening moving forward...What did i miss?
How did we get into crankcase pressure and side cover gaskets?
Liquid gasket is superior to a paper gasket in many instances.