10hp Briggs Flathead Build (non-SynchroBalanced)

Do it! Lol. I bet if you cut your seats and valves you'd gain all you would need and still need to grind the valve stems. That's a great opportunity for a 3 angle valve job which on it's own would be a big gain I'm sure but definitely check your valve to head clearance before you get TOO carried away! Lol.

I saw a video of a guy who welded and ground the lobes to create his own profiles but I don't feel that how he did was too proper.... you on the other hand could probably pull it off decently though! You're in the business... have any contacts that can spray weld? Not as in high heat/high feed "spray transfer" welding but actual spray welding, I'm sure there's a more technical term for it but I'm not sure what it is

Definitely gonna repeat the port and valve job I did on mutts oppy. That all worked great. I had considered welding up a cam but decided it was too much trouble. I’m just running the stock cam advanced a tooth right now.

You're running 1 tooth advanced! That's got to be like what 8 degrees or something!? That's huge but it sounds like it runs awesome! You must have advanced the spark timing to match it up eh?

Yep, one tooth advanced, not sure how much that is in degrees. For the ignition I just pulled the flywheel key and spun the flywheel ahead like two teeth, so about 6 degrees. Engine seemed to like all of that. That advance seems like a lot on the cam, but if you look at the data sheets on the racing cams it’s still not anywhere near as radical as them. My cam was opening the exhaust at the very bottom of the power stroke, the precision cams 212 alt cam opens like halfway down the power stroke.

This is the cam @Wheelinhorse has on his built oppy.

@RichieRichOverdrive 360 ÷ number of teeth = degrees per tooth. I'd be interested to know for sure what the Oppys are. I find it funny how universal cam and igntion timing is across all 4 stroke engines, even the 2.0L in my long gone '98 Golf was happiest with 6° advance and igntion timing dialed in. Old small block Chevys respond well to advancing nothing but the ignition via the distributor but anything over 10° was useless. Speaking of Chevys, the lobe centerlines and seperation angles are quite close to what you would get in a aftermarket cam for one...

This is all really great food for thought, I never would have expected that these little engines would respond well to advancing the cam a full tooth, I'm going to check mine and see how many degrees per tooth for a flathead single.

***edit*** 66 teeth so it's 5.45 degrees per tooth which makes for a plausible test!

Interesting, I just counted one of mine (18hp opposed because you got me curious) at 62 teeth.

Less than a single? Really? What's the OD of the gear? I'm looking at approximately 4-3/16" for the single.

That will take a bit as I was referencing a pic.  I do have a part 18 opposed i can bust open.  Might have one loose out in the building.

Yeah counted this one too, (18hp Oppy) it was 62 teeth.  It was in an awkward place in the back of the shed, but I came in about 3 7/8 inches diameter.





Trying to determine if I have helped get your topic off track or if it is good reference material for your engine build.

It's all good man I've been the one fueling this railroad! Lol.

Okay so they have about the same amount of teeth per inch then, interesting...

Most likely the same diametral pitch so the gear hobs at the factory can use the same tooling. There is actually a ton of common dimensions and engineering between all briggs engines, especially those older ones. 5.8 degrees sounded right for the cam advance, I think I did do that math once. I know I counted the flywheel teeth to have an idea of how much to advance the ignition. If i were you I'd definitely advance your cam! One thing you will notice, your exhaust will be louder than stock from the exhaust valve opening sooner! I run straight piped-ish and my hopped up engine is WAY louder than my old tired stock one.

Not a whole lot going on the last few days, I've been taking some cam measurements to know what I have and have been cleaning the block. Getting ready to start porting it soon  

I also got a new spark plug for it, a NGK BU8H marine plug, as you can see it sits pretty nice and flush with the roof of the combustion chamber compared to the old one!



It's a pretty cold plug but should be well suited to my needs!