Flathead to ohv conversion

Hello
Has anyone tried to use a Brigg ohv head on on a flathead engine. I have an old ohv with next to no compression but with a good head. It doesn't have to be practical or anything, but just a proof of concept. I was planning to just use the stock camshaft with some long pushrods. I'm not to worried about lubrication since this is only an experiment. I have a lathe, so machining to a degree is no problem.

Thanks for any idears in advance.

I don't think the head would bolt up? I'm not sure, can't say I've ever tried haha.

I thought someone here had thought about converting an oppy... didnt get too far if I recall.

It would be alot of work.

If it bolted up, biggest issue I see is getting the oil up there on the valves?

Yeah thats true, that's why the 18hp OHV Kohler K361 engines weren't so great. Is this engine a vertical or horizontal shaft?

It's Briggs and Stratton 4hp vertical shaft engine head and a standard 3.5 hp Tecumseh flathead also vertical shaft. As said i really don't care about lubrication to much since I just want it to be a proof of concept. If it works great I will find some way to lubricate everything. Ideally I want ridicules high compression to maybe run it as a diesel or at least semi diesel. For now I just have to se if the head will fit. I think I'm gonna have to drill some new holes in the head and the block, but that's no problem. The interesting part will be to find a head gasket.

Redlinemotorsports was going to try it with an opposed. It can be done as long as you can get things lined up ok. Lubrication shouldn't be much of an issue. You could just run the crank case vent into the valve cover before going back out. All the valve gear needs is a mist of oil to work, that's all they get from the factory. As for the gasket, Maybe you can use the OHV head gasket as long as you can find a way to bolt the head to the block.

sheet copper will work for the head gasket, and work well for the high compression you are talking about

I can see that working if they were both same name engine parts, like Briggs OHV head on a Briggs flattie block. The problem I would think is that the Tecumseh valves are backwards compared to Briggs engines. Meaning the Briggs intake valve pathway which is on the top or left, compared to Tecumseh which is either on the bottom or right. They do that so you can't swap parts.

Use a 5hp Briggs block. This is just guessing but, you can redrill the head bolt holes, center the head over the bore. The pushrod holes might line up but I think you will end up cutting that part out and maybe use tubing to cover pushrods coming from block to head. Make your own head gasket like Lawren said with copper. Use a plate to cover the pcv hole. Need to dish tips of lifters for pushrods to stay in place. And put the vent hole in the valve cover like Mr modified said but my guess is that there is already a piece of tube sticking out already for that. Longer coil wire.

That should be it.

Thank so for the info. I just checked, the valve thing is a real problem. I guess I will have to get a a Briggs engine from the junkyard. Maybe I could maybe also swap in a Briggs cam. I have a couple laying around. I also might use the ohv lifters. I will check if I can use them or if the dimensions are different. I also have to change the timing and use some sort of heavy flyweehl on the engine shaft. I will look further into it next weekend.

Thanks for all the info

Today I did some huge progress. The opposite valve location was perfect, since the head has the exhaust on the top just as the old Tecumseh. I drilled new holes in the head, but I might have to do another bolt on one side. The head is held by 3 bolts on one side and 2 on the other. I had to bend one pushrod to reach the lifter. I still have to put the tappets in my lathe and make indentations for the pushrods. They are just a loose fit in the valveguides but it should work. It is now an interference motor.

Looks great! Once you dish out the tops of the lifters I don't see why this won't work. Is this engine going on something once it's done?

The engine might go on a high power lawnmower, but im not shure. If my calculations are correct this engine should have abot 20.1 or more compression. So I might turn it into a diesel. I have a scrapyard close by, so finding an injection pump would be possible, but mounting the injector would be hard.
For now I´m just gonna work out a gasket, and getting it to run with out breaking. I´m not shure where to get copper sheet yet, but I´ll figure it out.
I´m also have two options for pushrods. I could drill holes at the right angles in the block, machine guides and make it proper. or I could do it like it is now. Just let the flop in the old guides and just make indent in the lifter.

20:1 compression ratio?? Might be a good idea to invest in some tougher interals. It would be real cool if ya got it to work though.

Nice man! That is a really cool project. If you had high compression I think a carb may work (at least for testing) to run on diesel.

I don't think a carburetor would work for a diesel because for a diesel, the fuel and air don't enter the cylinder at the same time. The fuel is injected in to the cylinder once the air is compressed.

Since a diesel doesn't require spark to run, just pull out the spark plug and put a fuel injector there. You'll have to time the injection point just right but should be possible. That would definitely be cool.

...cooler than it already is anyway

The carb won´t work for diesel since it would preignite worse then gasoline. It has a very low octane rating of less than 50. The problem with mounting a injector is that they are very long and need a specific taper. They also need to be bolted down to not pop out.
I´m gonna try to find a injection pump and injector from the scrapyard and use 1 of the 4 outputs. Rest are just gonna go straight back to the tank. (There are lots of 4 cylinder diesel cars in Germany).
I also think I need one more head bolt so the head wont warp.
Thanks for all the positive feedback.

Yeah you guys know more than me about diesels. Pretty cool anyway.