Need help with modifying a flathead engine

95 shaw said:
Awesome,

We just designed an overhead cam opposed piston engine.

Get the patent attorney ready for some work.

Up to you to just follow thru.



Thanks Bob!!!!!
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Actually, there's a 10 year old video which I forgot I had seen a few years ago where a very similar solution is implemeted. He offset the engines a little more to be able to install the spark plug on top. Another way he did was to install a pipe in the middle with the spark plug. But I'm sure that the compression ratio suffered quite a bit. And the scavenging inside the tube would be very bad.

The way I designed it allows for a very high compression ratio since you can make the valves go inside the cylinder and therefore the spacer can be really thin. But it makes it harder to install the spark plug. In a way, the spacer I modelled and had machined is almost the same. But I had to make it 20mm thick because of the spark plug. If not for it, I could make it much thinner and reduce the volume in the middle. Also, I want the cylinders to align, so I end up having the valves on the side instead of on top. But this opens up some very interesting options.

Anyway, there's quite some crazy stuff done with Briggs. I'll share the video with you. I found it again.


There are a lot more videos. Great content, actually. I don't know if you've already watched it.
 
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For a as designed prototype, I would go with no adapter, flat top piston, and a chamber machined into the block similar in design to the small block Chevy vortec engines at the end of the production run.
Spark plug between the valves angled towards block, designed into the block itself. Bump in chamber critical for turbulence.
Of course, ports designed for performance. A more aligned with the valve design similar to the blockzilla.
Capable of bigger valves, depending on application.

Make the block design symmetrical, so any 2 halves could be bolted together.

Might as well dream about modular sections, so, stack as many as you want.

If you are designing from scratch, go for the gusto.

Even more fun to think about.
 
You will notice in either of those videos, the flywheels were cast iron, not the lightweight aluminum design.

Just because we seem to be avoiding that subject. Lol
 
95 shaw said:
For a as designed prototype, I would go with no adapter, flat top piston, and a chamber machined into the block similar in design to the small block Chevy vortec engines at the end of the production run.
Spark plug between the valves angled towards block, designed into the block itself. Bump in chamber critical for turbulence.
Of course, ports designed for performance. A more aligned with the valve design similar to the blockzilla.
Capable of bigger valves, depending on application.

Make the block design symmetrical, so any 2 halves could be bolted together.

Might as well dream about modular sections, so, stack as many as you want.

If you are designing from scratch, go for the gusto.

Even more fun to think about.
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Well, if designing from scratch, I'd do some things very different ahahah But very nice ideas!


95 shaw said:
You will notice in either of those videos, the flywheels were cast iron, not the lightweight aluminum design.

Just because we seem to be avoiding that subject. Lol
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I'm sorry if I seem to be overlooking the subject. In reality, I don't have access to cast iron flywheels. I may try to find some but in reality it's not easy finding these engines here. Furthermore, I'd be afraid of messing with the timings, so there's that.
It'd be easier for me to add a flywheel to the output shaft, which I may end up doing if I indeed find that necessary.
 
I've been watching some videos and thinking about the breather tube. If I leave everything as is, with everything stock, do you think the engine would have issues running for the tests?

Worst case scenario, in my mind, some oil would drain to the chamber and, a little oil would come out of the breather tube (maybe not a little? I've never run these engines so I have no idea the real consequences of running them like this stock). What are your thoughts?

The carbs I'll probably leave stock. They were isntalled for these engines so should be adequate. I don't see any big advantage to me in installing some PZ19 carbs. In fact, I fear they may end up not working good because of the jets. What do you think?

These are my main two issues, and you've all given me a lot to think about. In a healthy and learning way, I must say!
 
alexbigmac said:
I've been watching some videos and thinking about the breather tube. If I leave everything as is, with everything stock, do you think the engine would have issues running for the tests?

Worst case scenario, in my mind, some oil would drain to the chamber and, a little oil would come out of the breather tube (maybe not a little? I've never run these engines so I have no idea the real consequences of running them like this stock). What are your thoughts?

The carbs I'll probably leave stock. They were isntalled for these engines so should be adequate. I don't see any big advantage to me in installing some PZ19 carbs. In fact, I fear they may end up not working good because of the jets. What do you think?

These are my main two issues, and you've all given me a lot to think about. In a healthy and learning way, I must say!
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Think the tube will work, short term. Do not connect to intake air before carbs.

Carbs should be fine. Still may require jetting change, due to the increased flow.
Depending on signal to the carb, may be rich, which is problematic.

Lean would only require reaming to a slightly larger diameter.

Adding rotating weight is a good plan. I forget that not everyone has built a supply of 'just in case' parts.
My daughter is going to hate the cool stuff in her inheritance.
 
Im on board with Mr Shaw .
I also say proceed as planned .
The breather as stated will likely spit out oil. Plug the hose if needed . Vent elswhere if needed . Get it together and fix any issue that pops up .
 
95 shaw said:
Think the tube will work, short term. Do not connect to intake air before carbs.

Carbs should be fine. Still may require jetting change, due to the increased flow.
Depending on signal to the carb, may be rich, which is problematic.

Lean would only require reaming to a slightly larger diameter.
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I was thinking of putting something like a chainsaw air filter or something else at the tip of the breather tube and that way leave the carb free of that oil.
That way, maybe putting the PZ19 would not be such a bad idea. That way I could try getting some larger jets and solve all issues. Something to consider.

95 shaw said:
Adding rotating weight is a good plan. I forget that not everyone has built a supply of 'just in case' parts.
My daughter is going to hate the cool stuff in her inheritance.
Click to expand...

This one really cracked me up! ahahahah
Who knows if she'll find a new passion later in life! Or make a small fortune on rare parts!

I live in Portugal, in Europe. I had the engines sent from the UK, some leftover stock.
Here we still find some flathead engines but they are kind of rare. Parts are quite expensive, the remaining engines are quite beaten up and new engines are a mirage. Still, for us here ate the University, flathead engines are really useful for researching which is a shame that they are not made anymore.
My professor prefers Honda GX series for small research projects since all parts are metric (the good old battle ahah) and readily available here.
 
I would do at least the initial startup for the baseline on the stock carb, just to make sure not to be chasing a phantom problem with the pz.
Might even do a couple pulls, since the dyno is new as well. For comparison. Once bolted to dyno, changes are a minor thing.

If you can get jets, and understand the metering rod, shouldn't be a problem.

After the baseline, you can make decisions on what you will need to get repeatable data.

I still think you will need a means of measuring air/fuel ratio, or EGT to effectively tune for data.
 
flattop1 said:
Im on board with Mr Shaw .
I also say proceed as planned .
The breather as stated will likely spit out oil. Plug the hose if needed . Vent elswhere if needed . Get it together and fix any issue that pops up .
Click to expand...
Awesome. I'll keep you posted in the meantime. At least, I now understand the main issues that may come up, And if they do come up, at least I may have solutions to solve them. That sure was very helpful of both of you!
 
95 shaw said:
I would do at least the initial startup for the baseline on the stock carb, just to make sure not to be chasing a phantom problem with the pz.
Might even do a couple pulls, since the dyno is new as well. For comparison. Once bolted to dyno, changes are a minor thing.

If you can get jets, and understand the metering rod, shouldn't be a problem.

After the baseline, you can make decisions on what you will need to get repeatable data.

I still think you will need a means of measuring air/fuel ratio, or EGT to effectively tune for data.
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Installing a MAF sensor should be no problem. We have already done that in the past. That way, I could at least compare as well if the intake is improved or not.

As for the air-fuel ratio, only way I can think of is installing a lambda sensor. Maybe that's something that I'll consider. It sure would give me more data to analyze. Thanks for the suggestions!

Testing both carbs I'm not sure that will be done. It depends on what my professor says. Maybe I'll try that. We'll see.
 
Direct Injection is needed, being carbureted long intake runners are need to reach the intake ports with that design. Having such long runners you lose pulse signal to the carb. Another thing that might be happening is puddling of fuel in one side of the cylinders and when cranked over the piston can push the fuel out of the exhaust port/intake port via compression before ignition, thus losing sync and no start.
 
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Thanks for your input.
I'm running a little behind schedule since I need some more parts.

Right now, I'm planning on running the engines almost stock (with no modifications to the breather) and we'll se how it goes. If I actually end up having oil coming out of the breather tube, I'll install a PCV Valve (I'm looking into a HONDA PCV Valve which i'd mount on top of the crankcase and disable the breather tube).

Also, I'm planning on running a PZ19 carb and getting a 0,3-1,6mm drill set (each drill size goes up by 0,05mm). So that if I need to increase the size of the main jet, I'll just drill a hole. It's easier for me that way.

However, I'm still undecided on which carb to use, actually. Prices are quite similar but because the intake port is 19mm, I think it's better to get a 19mm carb and increase the main jet (the engine is going to be tested mainly at WOT) then getting a 20mm or 22mm carb.

Also, I'll try installing a PLX or AEM AFR kit on the exhaust. But I'm expecting some issues since the oxygen sensor is supposed to be mounter on a duct about 24'' down the exhaust, not right next to the cylinder.
 
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