Cheapish stroker build

Deadman#73

Member
So I know about the 5horse crank in an animal but that's all I know. Kinda wanting to build one on the cheap and was really wondering what it's gonna take to put something like this together. I know it'll need a different rod for sure but another thing I'm curious about is a block extension to make more of a stroker. How much of the block would need to be clearanced to run something like that? Never built one of these but looking to make a little more power without sending it off and having a lot tied up in it.
 

flattop1

Dawg 89
Block extension can do two things . Allow more stroke or a longer rod or both .
It is also not a simple operation .
The 5 hp crank is way simpler .
Crank , rod , piston , bearings and cam gear.
 

CarlsonMotorsports

Premium User
Yea, there's a little more to it than just dropping the parts in, but you do not have to do a block extension to increase stroke and cubic inches.
Parts are all readily available as well.

The block extension (welding the deck plate on then resleeving and align boring) is pretty involved, even for the experienced.

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Jimbo

If you talk the talk you should walk the walk
I build engines with extended decks all the time.
There is more than one option for the rod length for the extended deck blocks.
One of the advantages of the extended deck is that the longer rod gives you a better rod ratio.
Another advantage is that it gives you a more stable deck than the die cast block. You get something better to bolt the head to and get a more stable head gasket surface. That's nice if you want to have a higher compression ratio.
Here's a picture of my deck extension plates:
1568913102192.png

$49.95
If you want to do it cheap you'll get out of it what you put into it.
The flat head crank was made for 5HP and a low compression flat head.
A good OHV stroker motor can make 4 to 5 times the HP of a flat head.
There are no new Briggs Flat head cranks being made anymore.
Are you sure you want to put a used one in it??
 

CarlsonMotorsports

Premium User
I'm now imagining someone purchasing the deck plate from Jimbo, bolting it on and wondering why it didn't run. :LOL:
PS...Don't forget the sleeve, the welder, the align boring machine, the mill, and the hone.
 

Deadman#73

Member
Well I seen someone else's post asking about the crank and you supplied an arc # number and it got the rubber burning on what else I could do with an animal and a buddy had an extension on his that sat for years. I'm not a person to put sketchy things together so putting a used crank in it wasn't really a plan and Brian I could see that happening as well. Even not being an engine builder I knew that just bolting all of it together wouldn't work you'd destroy the rings and possibly the Piston as Soon as it turns over lol. Thanks everyone for the input I really do appreciate all the knowledge you guys share.
 

Jimbo

If you talk the talk you should walk the walk
If you use a model 15 block with an aluminum bore, weld the deck extension on the inside of the cylinder and uses a piston and rings made for an aluminum bore or plate the cylinder with Nikasil you don't have to sleeve it.
I'd suggest welding the deck extension on the outside also.
 
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