• If you like antique engines, vintage tractors or old iron machinery, register and join us. When you register on Smokstak, please give complete answers and fill in the blanks. - IF YOU ARE ON WIRELESS OR SATELLITE, ENTER YOUR CITY AND STATE! NO ZIPCODES! All registrations are manually approved.

Wisconsin to the rescue!


3600 seems way to fast for that motor. And if you bump up the compression could you still hand crank it? It has electric start but I still get some satisfaction if I hand crank it, like when I would kick start my shovelhead at the bar.


Bumping up the compression will hardly do anything for that engine in regards to fuel economy. I say this because whether or not you choose to shave the head or install a thinner head gasket, you will soon run into valve clearance issues. You might only gain a point of compression, and it is just not worth the effort. At 1800rpm, your THD will consume approximately 3/4 gallon of fuel per hour under 50% load, and 1-1/4 gallon per hour under 100% load. That is not too bad for a 54 cubic inch gasoline engine.



Last Subscription Date
I respectfully disagree about some possible economy gains, Chris. The efficiency gains are not linear with increasing compression ratio, but are more when increasing a low compression to a less low ratio vs increasing a high to even higher. IE going from 5 to 7 will give more improvement than going from 7 to 9.

Also, being a flathead, the chamber volume is decreased more for every thousandth removed from the head vs an overhead valve engine. Assuming that there is step in the flat part of the head, and probably even if there isn’t.

Then you also have potential gains by tightening up the quench area.

But definitely we agree that you must watch your valve to head clearance. I think one could likely get enough increase to notice an improvement in efficiency, but likely not enough to make it difficult to hand crank.


Tracy T

Last Subscription Date
We shaved the head on a IHC cub, 4 cylinder flat head. No problem with the hand crank starting. The street we lived on was steep and the tractor had to low gear it before we did the work, after High gear was no problem. I also agree with keith's statement. And valve clearance should be taken into consideration no matter what engine you are working on when shaving heads or milling the block along with piston clearance if you really going to hog off a lot of material. this being a flat head a competent machinist could take a little out of the valve recess in the head to get a little more but likely not worth the effort unless the combustion chamber in the head is large.


I have 3 yanmar engines to use for parts, if the Chinese did their job of reverse engineering they should be the same.


Ah that is a beautiful engine. I'm putting one in my truck I like them so much. I don't care how much fuel it drinks, cause the last engine I had in it had a broken ECU that somehow managed to drink 5 gallons in 35 miles or less, and that was a 4 cylinder.

I love the engine because I hate computers. I'm gonna pull the head off and check for piston play to see maybe how much h life it's got left. It did live as a concrete saw, so I only hope they kept the filter clean. If not, yikes. It seems to have decent compression though. I do notice that when I rev it up fast a huge white cloud engulfes the immediate area surrounding the engine, so I know it's got personality and a leaky carburetor gasket. Poor thing needs a tune up.


Staff member
Last Subscription Date
I used to frequent a scrap yard that got a lot of concrete smoothers with Wisconsin engines (usually ACN or BKN) on them. On some of them, you could move the piston 1/8" to either side. Many had been bored out 0.030" already.