1st go-kart project advice

[nstiesi]

Hi all! 1st post here.....

Some years back I hired a lawn service and junked my lawn mower that was originally purchased for $50 at yard sale. It ran, but the motor had a miss and clearly needed work. I LOVE engines and tinkering, but didnt have time or use for it, so I removed it, tossed the frame, and it sat in a cabinet for the last 5 years.

I have impulse control issues when it comes to making, and last week I decided it was finally time to build a kart. I am starting from SCRATCH. The motor is vertical shaft, and after a week of reading and research, I decided on a Peerless 700 transmission to provide right angle power output, reverse, and a "range box" (I do NOT plan to shift on the fly).

This brings me to my question. After all these years, I never paid any attention to the power rating on the mower engine. I figured people used mower engines for karts "all the time", so whatever it was would be fine. After dusting it off and reading the plate, the answer was 4.25HP. So the TL;DR question is, would this be enough?

Now I have done enough reading to know that no one can answer that without knowing some other things about gearing, tire size, and what I want out of the kart. I dont know all these answers, and I am at the VERY VERY beginning of this process, but I can say that the transmission is 5 speed, and I estimate the ratios to be from 1:4.5 to 1:1.8 (I still need to open it and count teeth, or at least make some marks and count turns. My estimates come from heymow.com guides on the tranny, but there are a many different arrangements and configurations). I am thinking a 10" tire, pavement and grass only, no off road. Target speed maybe 20-25 tops? NOT looking to build a death machine, just some family fun. I have a 7 y/o son I want to build with me, and as he gets older teach him to drive it, so speeds must stay low, at least at first. (the range box aspect of the tranny should help. I could also govern it).

Whew, I got a little long winded there. All I really need to decide right now is, should I be engine "shopping", or should I cut my teeth on the 4.25 and see what happens? I dont want to spend the time rebuilding it just to decide it isnt strong enough (although it would still be fun, and a learning experience, so there is an argument in favor)

Thanks!

 

[madprofessor]

That transmission to make your vertical shaft work for a kart costs more than a brand new and warrantied Predator 6.5hp. 212cc horizontal shaft engine from Harbor Freight, $120 on sale right now. A simple screw limits its throttle range for the kids.
All those gears in the Peerless would be kind of wasted on a low hp. engine like yours anyway. Except reverse, that's always desirable.

 

[nstiesi]

I know it sounds silly, but I am a bit of a junker, and part of the project's appeal was to use what I had on hand and get a chance to tear down and rebuild a motor.

Now, that spiraled into buying the 700 and you are of course 100% right; in hindsight it doesn't make much sense and if I could do it over, I'd probably just grab the Predator and be done. Maybe on my 2nd build! lol

I would be willing, at this point, to try and snag a higher HP vertical mower engine, but only if it makes sense to do so. I have been chasing a 6.5 HP Briggs on OfferUp for pennies. Should I see that through if I am stubborn and insist on using the 700?

At least I will have reverse!

Thanks for the reply!

 

[madprofessor]

Not if you're serious about the teardown. That's what karting is about, having fun with whatever you've got or can get. If the engine work appeals to you, by all means go for it and make it run, maybe learn stuff.
I spent well over $300 on hi-perf parts to make my $100 Predator 6.5hp. turn at least 15+hp, when I could have bought a Predator 13hp. engine 420cc brand new for even a little less than that. Some cheap easy mods would have matched my 212's hp. today.
That's because I wanted the fun of building a race motor that's even faster than my last one. Wrench on that motor if you want to, and maybe have something when you're done. Might find happiness with that one, or decide to trade up once you know.

 

[nstiesi]

So I ended up getting the 6.5 HP Briggs for $20 (its a 120000 series, 196cc). I spent this week stripping it down (my first engine! It was fun...mostly; except for the two motor mount Taptite bolts that broke, then broke my speed out, and had to be milled out to a through hole). I dont have photos at the moment, but the cylinder does show some scoring. A few places it can be felt with a finger nail, but I dont think it is TOO bad. (again, 1st timer here. I am an engineer by trade, so I have the background and theory, trying to get the hands on experience now)

So bearing in mind this is a $20 engine, should I:

A) Not worry about it. Clean, re-assemble with requisite renweal items (already have all gaskets, seals, carb rebuild, plug, air filter...all for $25)

B) A reconditioning hone with a flex hone just to knock down some ridges and get a cross hatch. (Will this require new rings? Rings are $30, Honing tool ~$40, plus I will get some telescoping gauges to make sure the bore is to spec)

C) Junk it, cut my losses. (I dont think this is necessary. I'm sure it will run, even if not optimally. Part of this was for the learning of it, so I am not really considering this at the moment)

I am not trying to be SUPER cheap with this, just smart. I am not expecting to build a kart from junk, cut every corner, and end up with a nice result. I will spend the money where I have to.

Thanks!

 

[madprofessor]

Great job on finding the cheap motor and parts, and having all those parts means you definitely should try to get it running, it's all already paid for anyway.
Looked on ebay under "Briggs cylinder hone", there's tons of adjustable 3-stone (some fixed, some w/3 each of 100, 240, 400 grit) hones for about $18 and on up. Some are 2" - 7", 0.75" - 2.5", 51mm - 177mm, etc.
Adjustable means having something that maybe will get another usage later.
Don't know enough about Briggs to say if a honing is even necessary. Do know that bore wear can create a lip at TDC that invites a broken top ring if revved hard to maximum.

 

[nstiesi]

I will look at ebay. Harbor freight has one too.

Right now I am thinking I will try the hone and leave the rings, then clean it and try to get her running.

 

[madprofessor]

You said you can feel some scoring with a fingernail. I'd rotate the motor around to TDC, just to see where the top ring stops when at TDC.
If that motor was broken in by the original owner per the owner's manual method, a certain couple of rpm revs for a certain time, you can bet that the proverbial "scare lip" started forming at TDC. If it was operated in whatever installation for hours with the governor still in operation, there was a scare lip for sure. Feel for it.
Hone that lip out if it exists, keep feeling for it.
Dirt bikers in my day all too often bought a bike from somebody, then went and wrung it out full-throttle race-fashion immediately. Previous owner putt-putted it for years, wore a big scare lip in it, then the heat and piston velocity of suddenly being wrung out would cause a sort of stretch (what we called it) making the top ring slam against the lip and break.

 

[nstiesi]

Thanks for the advice! I read about the "ridge" where top ring stops earlier today. I see a bit of a pattern about 1/4 from the top of the cylinder, but I cant really feel it. I think I will hone anyway just to be sure. I'm gonna grab the telescoping gauges too just because I hope this wont be my last engine and they will be handy to have around, so I will at least measure the bore to see if it is to spec. I measured some crankshaft journals and they appeared to be in spec to the B&S repair manual.

 

[Denny]

If there is a ridge use a ridge reamer then hone. If the engine ain’t smoking I’d leave it alone. On a first kart stick with a stock engine at first. Then after some seat time you can decide what you want out of the engine and follow the lemmings and build it as your experience allows. Stock can be more reliable = fun on a first kart.

 

[madprofessor]

Once again Denny sounds like the voice of experience, and I'll agree. If not smoking or clacking leave it alone and enjoy it.
And anything that means more reliability does indeed mean more fun on a first kart.

 

[nstiesi]

Thanks for all the advice! I did not find much of a ridge at the top, so I dont think ill need to ream. I went ahead wit ha hone last night, and I think it turned out pretty good. I can no longer feel any scores (though some are still barely visible underneath the cross hatch). I hit it three times, maybe 10-15 seconds each, cleaning and re-oiling between each run. Was afraid of going to hard. I measured the bore before and after in multiple places and found almost no difference. The bore is measuring within .001 of spec to the Briggs manual, so I think it will work fine. Next I gotta clean up those valves and the gasket surface.

To be honest, I didnt try to run this engine before taking it apart, so no idea if it was smoking. However, I am learning a TON and having a blast so, definitely worth it!

 

[Budget GoKart]

my ytip to you is if you cant find something look outside of the box to find that part.

 

[Denny]

In my experience unless you replace the rings it will smoke now.

 

[madprofessor]

A nice cross-hatch on the walls will hold more oil. If that means it smokes a little, the trade is well worth it. Some serious timing advance would mean it doesn't affect the complete burn of the mixture.
Is that the smoke you're talking about? Why would new rings not smoke also?

 

[nstiesi]

I just CANT find new rings for less than $30. The rings look good. The cylinder measured very close to spec and very close to round at 3 different depths (all 9 measurement within .001 of spec). I could take the rings off and measure the end gap, but I almost dont want to know, lol. I have no reason to think they wouldn't pass based on the condition of all of the other parts I have measured.

For my total of $46 investment (for the motor plus the gaskets/plugs/air filter), I am going to roll the dice on a little smoke. I think I will learn something either way!

 

[madprofessor]

Running the old rings is free, and you enjoy doing this stuff anyway. Worst that can happen is needing new gaskets again if you replace the rings later. Smokey the Bear won't hit you in the face with his shovel over a little blow-by smoke.
Speaking of blow-by, make sure to clock your ring gaps opposed to each other. 3 rings = 120 degrees apart for ring gaps. Same for 3-ring oil seal ring assembly, 120 degrees apart for each. Treat top ring of the 3 as the one you clock 120 degrees from the rings above it.
Ring gaps lined up guarantee some blow-by into the crankcase, more smoke, less power.

 

[nstiesi]

Noted on the staggered ring gaps. Thanks!

Last night I cleaned the valve housings and gasket surfaces and washed the block thoroughly. I am going to white cloth test the cylinder and wash again if necessary. Then I need to clean the carbon from the piston face and I will be ready to re-introduce. I may also lap the valve seats after I clean the carbon from the valves themselves.

 

[madprofessor]

Just looked at a youtube video (because curiosity) on "Removing Carbon From Piston, Cylinder Walls, and Block Deck" to see about cleaning a piston face while it's still in the block.
Surprised to see what a great job WD-40 did on it. Guy used a trigger sprayer can, not the messier aerosol, and sprayed down the pistons, block face, all of it, and let it sit for a minute. Then he used a scraper on the block face.
After spraying the pistons again, and leaving it another minute, he only wiped at the badly carboned pistons and walls with a green Scotchbrite pad. No scraper, of course. I was just stunned to see how shiny clean it was simply wiped to become. Carbon-free, clean and shiny, amazing.

 

[nstiesi]

Cool, Im gonna check that out!

I went at the valve housings with a brass brush and lots of WD. Avoided the seats and the intake valve seal that is pressed in a blind hole and wont come out. It came out pretty good, but the walls in the valve housings are very rough from the casting so it was hard to get it all.