eBay home made OHV for a 5hp Briggs?
- Thread starter Thepaetsguy
- Start date
Agree, this is an overhead valve not overhead cam. What you would need is a structure over the top to hold the rocker shafts.
Problems I see with it, the valves are canted at a roughly 45 degree angle so it would need some creative rocker setup to translate the up and down from the push rods and what structure is created for this would have to be held by the head bolts (not the best idea). The hemispherical design would create a drop in compression from stock and would likely require a domed piston to get back to where you want to be. The spark plug boss being right over a head bolt may cause some clearance issues.
Problems I see with it, the valves are canted at a roughly 45 degree angle so it would need some creative rocker setup to translate the up and down from the push rods and what structure is created for this would have to be held by the head bolts (not the best idea). The hemispherical design would create a drop in compression from stock and would likely require a domed piston to get back to where you want to be. The spark plug boss being right over a head bolt may cause some clearance issues.
The ad stated the sparkplug hole was not drilled and that is something the buyer would also need to do.
But that still just leaves me looking at it wondering what someone was thinking? The ad stated the head matched and came with a stock 5hp Briggs head gasket.
Could they have meant to run an heavily angle SBC Style rocker off of each of those head bolts?
I figured the plug hole with discretion could be angle drilled on whatever side of the valves the buyer chooses? Or like titanic levels of aluminum welding for a place up top to put a cam. But if the cams up top where to put the plug?
But that still just leaves me looking at it wondering what someone was thinking? The ad stated the head matched and came with a stock 5hp Briggs head gasket.
Could they have meant to run an heavily angle SBC Style rocker off of each of those head bolts?
I figured the plug hole with discretion could be angle drilled on whatever side of the valves the buyer chooses? Or like titanic levels of aluminum welding for a place up top to put a cam. But if the cams up top where to put the plug?
The problem with making this an overhead cam design is the crankshaft runs parallel to the valves. in order to turn the cam you would need a 90 degree conversion, like a bevel drive to turn the camshaft. the boss for the sparkplug hole looks very close to where the head bolt head would be, add that this is an aluminum casting and would need to have hardened washers under the head bolts and it looks like an interference issue to me.
The only reason i can see to change a flathead to an overhead valve (or overhead cam) would be for increased power/engine speed. In that case, it would need to be a much more rigid rocker or cam setup to deal with the stress if you are trying to beat the power and speed of a built flathead 5hp.
This is just my opinion, the casting looks like someone put a lot of time into it and maybe they have a vision I cannot see.
R
The only reason i can see to change a flathead to an overhead valve (or overhead cam) would be for increased power/engine speed. In that case, it would need to be a much more rigid rocker or cam setup to deal with the stress if you are trying to beat the power and speed of a built flathead 5hp.
This is just my opinion, the casting looks like someone put a lot of time into it and maybe they have a vision I cannot see.
R
I can see the plug boss but I don’t see that being an issue. Next the way the head would bolt to the block the plug would be angled straight out of the front of the block.
I’m guessing that lower rectangle portion in between those two head bolts would get milled out to allow to pushrods to stick up through the stock flathead pushrod holes.
Past that wizardry? I do no OHV’s can leak oil onto the ground for all it cares as long as the combustion chamber has a ring seal.
I’m guessing that lower rectangle portion in between those two head bolts would get milled out to allow to pushrods to stick up through the stock flathead pushrod holes.
Past that wizardry? I do no OHV’s can leak oil onto the ground for all it cares as long as the combustion chamber has a ring seal.
Always fascinated with these projects but I’m no engineer. I was attempting to build OHV conversion for a flathead Briggs as a teenager and project was far beyond my abilities. I settled for a home brewed fuel injection build for it that ran on dad’s Laquer thinner until he found out. Afterwards I ran model anirplane nitro fuel and it ran like shit and sent a rod out of the motor. Fun times.
I would expect flathead to OHV conversion in aluminum Briggs would require a few obstacles to allow pushrod movement. Rocker arm travel will impart sawing motion on pushrod. Shorter tappet solves part of that problem. Valve guides don’t have enough material to elongate bores and smaller diameter pushrods may not have enough rigidity for the application. Valve lift is reduced by leverage ratio of rocker arms. These issues could negate some or most of the advantages of an OHV conversion. @Thepaetsguy has attempted OHV conversion previously. I’d like to see that one running. I still think it’s a cool build
I would expect flathead to OHV conversion in aluminum Briggs would require a few obstacles to allow pushrod movement. Rocker arm travel will impart sawing motion on pushrod. Shorter tappet solves part of that problem. Valve guides don’t have enough material to elongate bores and smaller diameter pushrods may not have enough rigidity for the application. Valve lift is reduced by leverage ratio of rocker arms. These issues could negate some or most of the advantages of an OHV conversion. @Thepaetsguy has attempted OHV conversion previously. I’d like to see that one running. I still think it’s a cool build
I had a pile of parts in the early eigthies. I had a Briggs 5 horse and a Honda CT90 OHC head, tried to rig an external timing belt...no oiling...so I enclosed the head to have its own oil reservoir. Never did figure out how to connect a belt from the crank to the cam. I still think that is the way to do this. Eventually, I will figure out how to do it without spending more than it's worth. Until then, it lives on another back burner.
Posting here has reminded me of some of the stuff I had spinning around in the back of my head over many years. I built many engines back in the day. My shop always had dozens of motorcycle and kart engines laying around. I once picked up an old Honda ATC 110 cylinder head and put it on a Briggs flathead motor as a gag for another mechanic. After a bit of study it had me wondering if it was a worthwhile effort. Cam drive was the sticking point. Oiling the top end is simple enough. A pressurized tank with hand pump will keep it happy just like the old hand pump Indian motorcycles from early 20th century. The very early machines used total loss oil system with open crankcase. Spent lubricant dumped onto roadway. Keeps the dust down on those old dirt roads…