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Messages - Dancer

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Briggs Flathead / Re: Need help w/ cylinder head
« on: July 11, 2018, 01:13:13 pm »
A big thank you to PJG56 and rotten ron for all the great information.  And PJG56, l am interested in those high performance engine parts so please let me know how much you want for them.  I guess we would initiate all that via email (but if that doesn't work I can just give you my mobile number).  My only hesitation about changing the cam, piston, crank etc. is that I have zero experience building a "flattie".  Truth is, I've never rebuilt any engine.  With car engines, I always drop off the short block at the machine shop, do my own cylinder head porting, then drop off the heads for a performance valve grind and have them re-assemble the cylinder heads.  Once the short block is done and the heads are rebuilt, I bolt everything together for a complete longblock and get a buddy to help me install the engine.  I guess if I get in over my head, I could have a small engine repair shop re-assemble everything.  Again, thanks for all the help so far; I'm looking forward to this process (and finding a local racing venue).  BTW, about 20 years ago I did about a third of a sprint Kart racing season.  I actually bought the Kart for my son but he was intimidated with mixing it up on the track so I raced it.  Because of the kind of engine I had (a two stroke Italian high revving mill), I had to race against 12-16 year old kids!  I thought I would do very well because they all had Briggs & Stratton engines and I thought a 2 stroke would crush a flathead 4 stroke.  I was the one who got crushed and I learned to respect those B & S engines. 

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Briggs Flathead / Re: Need help w/ cylinder head
« on: July 10, 2018, 12:33:42 pm »
I called an automotive machine shop yesterday and they suggested that I bring my engine over to them; they think they can do a performance valve job on my 12 hp B & S.  I think I'll be compelled to keep the stock valves; I've searched and searched this forum but I just haven't been able to find the information I need to know about what size I would buy for enlarged valves.  Plus there is the issue you raised about valve shrouding; I could end up spending a lot of money on machine work and valves for no gain in hp or torque.  Maybe I can get more flow with a new camshaft which has higher lift cam and / or longer duration.  I'm going to try to call ARC Racing; perhaps they are willing to share some ideas with me about prudent engine mods, including a proper camshaft for my application.  Anyway, one of the next steps is to take the engine to the machine shop and have them compresses the valve springs and remove the keepers so I can do a mild port job on the intake and exhaust passages.  One of the other areas I'm pondering is carburation.  I've already rebuilt the stock Walbro carb but I'm wondering if there is a better option, i.e., after I slightly increase the air flow, will I need to change the jetting and does the Walbro carb give me that option?

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Briggs Flathead / Re: Need help w/ cylinder head
« on: July 09, 2018, 11:57:56 am »
I don't know what the compression ratio is for a stock 12 hp B & S but it probably isn't much more than a 1942 Harley.  I'm still wondering if the reduced compression from porting the eyebrows is worth the marginal increase in flow.  Today I'm calling local machine shops to see if I can find one that will do a valve job on a B & S engine... and I'm still searching this site for ideas and specs. 

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Briggs Flathead / Re: Need help w/ cylinder head
« on: July 07, 2018, 07:06:03 pm »
Progress!  Buddy came over and helped me remove the engine from the mower chassis (after we first removed that big round thing under the mower).  Those briggs engines are heavier than I thought.  I also took off the cylinder head to see what is going on.  The cylinder looks good; still has some cross hatch.  The exhaust valve is a nice brown color but the intake valve is black; not sure what that means.  Anyway, I'm searching this site to see what I'm supposed to do next.

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Briggs Flathead / Re: Need help w/ cylinder head
« on: July 06, 2018, 12:19:40 pm »
Again, thanks for the valuable advice; I figured some of the engine internals would need to be upgraded.  What I didn't think about is that I could spend a fair amount of money on machining and larger valves, only to end up with less hp because of reduced compression.  Because of my ignorance about B & S engines, what I really need is a how-to-hot-rod-Briggs-&-Stratton-engines book.  I've searched on amazon and google; there are several youtube videos, some wiki how-to sites and lots of already build race engines but I haven't been able to find "the book".  If anyone knows of a book that I can buy, that would be greatly appreciated; something that tells me specifically what I need to do to reach my goal of a 30 - 40% increase in hp and torque.

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Briggs Flathead / Re: Need help w/ cylinder head
« on: July 05, 2018, 12:17:51 am »
Thanks for the information, I have zero experience building a flathead engine; some experience with traditional over head valve car engines but none with B & S flatheads.  BTW, the pop riveted engine tag says it is model # 283707 and type 1139-E1.  I'm hoping to find a source that will definitively tell me how big I can go on the intake/exhaust valves and from what I've read, there is an alternative to modifying my cylinder head; apparently a 10 or 11 hp B & S cylinder head will bolt up to my 12 hp model.

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Briggs Flathead / Re: Need help w/ cylinder head
« on: July 03, 2018, 05:12:22 pm »
Sorry, that should read, "... as a noobie..."

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Briggs Flathead / Need help w/ cylinder head
« on: July 03, 2018, 05:10:24 pm »
I have a Murray rear engine w/ 12 hp B&S.  It needs a valve job anyway so I'm hoping to get some more hp and torque as I do the repair and as a nookie I have a few questions:  1)  Can I replace the stock valves with larger diameter?  2)  Is it possible to do a 3 angle grind on the valves and does it do any good.  3)  After porting the "eyebrows" I'm going to lose some compression.  Is there an available "how to" about welding material to the roof of the cylinder head to raise compression?  (And yes I did search before posting my questions)

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Newcomers / Great News !!!!
« on: June 24, 2018, 05:48:43 pm »
My wife insisted on taking our 12 hp Murray "forest gump" mower to the local small engine repair shop and they told her it has a bad valve; since the cost to fix it is more than the mower is worth, it is mine to hot rod.  I will be searching this forum for ideas but any help is appreciated.   

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Newcomers / Re: Broken Mower = New Hobby
« on: August 03, 2016, 11:58:55 am »
Thanks!

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Newcomers / Broken Mower = New Hobby
« on: August 01, 2016, 07:05:10 pm »
This always starts the same way... something breaks and I can't seem to put it back together without trying to get more power out of the engine.  What I have is an 11- 12 year old Murray Select 30" rear engine mower with a 12 hp Briggs & Stratton engine.  I may not get into racing but the simplicity of this B & S engine appeals to me.  I've tried to find go fast parts by googling Briggs & Stratton 12 hp model # 283707 but I honestly haven't been able to find the kind of parts I want.  Is there nothing for my old B & S engine? 

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