5hp i/c stock piston limit?

#1
Does anyone know what is the stock piston rpm or power limit? I'm thinking of using the stock piston with new rings from my Briggs with the arc stock length rod and 94ss cam I have but I'm wondering if it can handle the increased rpm and power. It had great compression, didn't burn oil and the cylinder has no scratches. Before anyone tells me to just get it bored out, I don't know of any shops near me that work on these engines. Plenty of machine shops for cars but I would rather take it to someone familiar with this engine. As for shipping it to a shop.... more money than I would like to spend on that one thing
 
#2
The stock piston should be able to handle the build your talking about just fine up to about 6-6.5K rpm. The steel bore in the I/C engines wear much slower than the aluminum bore engines, so its common to see them with very little wear in them. You will need to at least hone it, if your installing new rings. Sounds like a fun build, are you planning any other mods to the engine besides the cam, and ARC rod?

Matt
 
#3
The stock piston should be able to handle the build your talking about just fine up to about 6-6.5K rpm. The steel bore in the I/C engines wear much slower than the aluminum bore engines, so its common to see them with very little wear in them. You will need to at least hone it, if your installing new rings. Sounds like a fun build, are you planning any other mods to the engine besides the cam, and ARC rod?

Matt
I was looking at a more powerful can but a lot of people say the 94ss will be good. I was also looking at buying a tilly carb but since ilk have to buy a different gas tank I think for now I'll just buy the arc flywheel and mod my original carb. I don't have much money for this right now and I'm getting tired of the governor on my Tecumseh 5.5hp power sport so the sooner I get this engine running the better
 
#4
Good info Matt

I would think a good stock piston with proper clearance will work fine for your build. Is it the best piston, no, but it will suit your needs. Since your engine is iron bore you "can" run a tighter ring end gap than a kool bore engine. Only if your bore is straight and uniform.

The 94ss cam is certainly an improvement over stock. It's conservative compared other cams available. You are most likely going to need new valves to get the lash set.
 
#5
I've never run a non stock piston, don't know why.
I have one now that I've had up to 9400 a few times. I recently tore it down and it's ok. http://youtu.be/aQaGwhLmM0k

When I was 14 to 18 I had a similiar build to what I have now, huge cam, had a bigger tillotson carb back then but I didn't have a tach. I had a Horstman rod. I pulled the pin out of the bottom of a stock piston once.

This was back in the mid 80's and I had no idea where to get high performance parts.
The rod was ok, except for where it got beat up from going up and down in a cylinder with no piston on it. I had to grind the sides down flat again. This was an aluminum bore so it left four deep grooves below the piston ring surface of the cylinder.

I worked them out with a die grinder, threw it back together with another used piston.

Used to tear that thing down a lot just for something to do. One thing I learned is that when things get loose, especially the big end of the rod, it will crack pistons on the bottom of the pin bore.

So now that we have ebay and forums, I'd say either look for a standard Wiseco piston and use that, or tear it down often, or plan on ruining that ARC rod.
 
#6
I was looking at a more powerful can but a lot of people say the 94ss will be good. I was also looking at buying a tilly carb but since ilk have to buy a different gas tank I think for now I'll just buy the arc flywheel and mod my original carb. I don't have much money for this right now and I'm getting tired of the governor on my Tecumseh 5.5hp power sport so the sooner I get this engine running the better
The 94ss is good choice, especially if you don't want to get any machine work done. Like Rupster 86 already stated, you will probably need new valves to get your lash correct, and being your engine is an I/C type you probabaly have a valve rotator on the exhaust side that you are going to need to do away with anyway. I'm using a Dyno 03ss cam in my I/C build, which is the next step up from the 94ss, but it required me to buy the +.100 lifters to get my lash correct, and I also had to buy a special tool to cut the valve spring pockets, as I was running into coil bind with its .290 lift. You shouldn't have this problem with the 94ss. Like Rupster 86 also said, you can run a tighter piston ring gap to get a better cylinder seal. The way you do this is to buy .010 rings (if your bore is STD), and file fit them to the proper end gap. Like you, I'm not using any machine shops in my current I/C build, everything that's getting done, I do myself. Here is a link. http://www.oldminibikes.com/forum/b...s/80440-briggs-high-rpm-poor-boy-special.html

Matt
 
#7
Yeah I'm familiar with your thread, I've read it a few times :laugh: the first time I read it I looked on eBay to find fantastic deals also but no luck. Your thread motivated me that I can do this with a budget and since I just bought a house and my wife had to stop working for a month I'm just catching up on a few things. I really have waiting for something I want (like this build) so I've sold a few things I had as my previous hobbies. Anyone want to buy a mcpx v2? Ha ha ha
 

CarPlayLB

Well-Known Member
#9
I have a Wiseco #1993 stock sized piston I can part with cheap! ...and I have a Horstman standard length rod that needs new bolts and bearings...can be had cheap too! PM me if interested
 
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