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Briggs 18 hp Horizontal Opposed Twin Knock

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Re: Briggs 18 hp Horizontal Opposed Twin Knock

Postby bgsengine » Fri Apr 25, 2014 9:06 pm

HondaG100 wrote:
bgsengine wrote:It is an L-Head, aluminum block, I am going to make a bet that you will find a loose valve seat.


Right on BGS and Deere! Beer is on me. :D Number 1 exhaust valve seat pulled out by hand. The exhaust valves both looked like they run hot. Almost white. It does not run hot or lean so maybe I have an issue with loose exhaust seats not transferring heat correctly? Oversize seats the solution here?


if you can GET them - replacing seats (and getting them square) is something a machine shop would be doing, unless you have the tool kit to counterbore, ream and install the new seats, get them squared up, then recut the seats 90 degrees to the guides - prolly looking at $600+ worth of special service tools to do the job.

However - I *HAVE* , for an "in a pinch" , "Absolutely no guarantee whatsoever as to quality or how long it lasts" repair job, install the seat, install valve normally, then use a center punch , peen in the block all the way around the seat, as closely spaced as possible, multiple passes, until seat will not turn at all by hand, then remove valve, set clearance, lap it in..

The one I did - and keep in mind it was only ever the ONE time I did any such thing for anyone (even me) is still running 15 years later, with nothing more than standard maintenance.

the general idea being, the installed (with spring) valve holds seat square (of course after cleaning the area where seat sits) - Of course, if the seat is already damaged or cracked, all bets are off then.

but if you want a properly done job, I'd suggest having seats done at a machine shop - probably cheaper than buying your own tool set.

*edit* - Or, what Walt said - There IS a procedure to peen seats back in in service manuals.. I forgot all about that til he mentioned it. :)
How poor are they who have not patience. What wound did ever heal, but by degrees? - Iago (Othello Act II, Scene 3)
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Re: Briggs 18 hp Horizontal Opposed Twin Knock

Postby RoyM » Fri Apr 25, 2014 10:38 pm

That was a common problem. I staked the seat in three places with a center punch then followed with a drift punch around the circumference. Dress the seat if you have a Neway cutter and replace the valve. Grind the tip to establish proper clearance. That is one smooth running engine, take care of it as parts are getting scarce.
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Re: Briggs 18 hp Horizontal Opposed Twin Knock

Postby HondaG100 » Sat Apr 26, 2014 7:03 am

Email sent Walt. This engine is worth some machine shop work so I will likely go with oversize seats but I need the service manual anyhow. Can a Briggs dealer usually get oversize for something this old and if so what part number do I need? Thanks guys.
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Re: Briggs 18 hp Horizontal Opposed Twin Knock

Postby Deere2me » Sat Apr 26, 2014 7:25 am

HondaG100 wrote:Email sent Walt. This engine is worth some machine shop work so I will likely go with oversize seats but I need the service manual anyhow. Can a Briggs dealer usually get oversize for something this old and if so what part number do I need? Thanks guys.


Briggs part lookup here:http://www.briggsandstratton.com/us/en/support/manuals/engine
You might wanna check out some lawn tractor hot rodding sites about OS seats etc. I dunno.
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