Time to be rebuilt!!!

Quick question for you guys, what is the worse things you have seen when a flathead it beyond a rebuild? Is it just a slight loss of power, or a big one? Is it a lot of smoke or flames shooting out exhaust without actually backfiring? Mine is doing the latter and I assume it's because it is over due. Last time I freshened it up I honed the cylinder and replaced rings on a used piston. I done them the best of my ability with the knowledge and resources i had available. The guides were decently sized to the used valves. I have ran the snot out of it for quite a while. I changed oil about ever 2 hours or so. And lapped the valves every 6 to 8 hours. I probably have 18 maybe 20 hours total run time on this build. With the last hour or two I can feel a sharp decrease in overall performance. I love flat heads but I camt imagine being on a racing schedule and trying to pay someone to keep one of these dudes in optimum condition. A man would go broke lol.
 
Valve Guides are the biggest thing in my opinion . the inner cam boss can wear as well , which is hard for a commoner to fix .
Obviously cut the valve seats and ne w valves and springs . Fresh bore .
Guides are the worst thing .
 
Valve Guides are the biggest thing in my opinion . the inner cam boss can wear as well , which is hard for a commoner to fix .
Obviously cut the valve seats and ne w valves and springs . Fresh bore .
Guides are the worst thing .
How would someone go about fixing the boss you mention? Oddly enough I have not considered what to do if failure occurred.
 
A lifter bore guide is easy enough to install, but you may have other issues -- that isn't causing the flame through your exhaust.
That is likely a fuel or timing issue. Possibly the flywheel slipped and is not at, or very close, to TDC, which would kill the power as well.


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🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
33 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
Sounds like your valve lash closed up and your exhaust valve isn’t closing. I tried running .004” lash years ago and it closed up when hot and did the same thing.
 
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