Gas engine selections and prep

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Gas engine selections and prep

Post by rkcarguy » Tue Oct 10, 2017 1:04 pm

I thought I'd share a little relative info regarding the small Honda and Honda "clone" engines and my experience with them.
I'm in my early 40's and since 2011 I have raced go karts, this year and probably next year I'm taking a break as I'm building a home.
I raced on asphalt with a 4-stroke kart, which can be powered by a GX200 motor or "clone" engine. Depending on what we've done to the engine as far as modifications, decides the kart+driver weight. Must run on pump gas.
Now we run these engines hard, upwards of 7000 RPM in the heavy weight modified class, but I've got lots of friends with yard karts mini-bikes and so on using the same motors in stock form +/-, and the same things can and often do apply. We have found that the Honda sadly is not made in Japan anymore. They are made in Thailand. While Honda still has better QC standards, they aren't what they used to be. Racers that wanted to use a GX200 for modified try to find older ones. More meat in the castings and more solid crank shafts. We found that certain harbor freight engines have different internal builds and are suited better for different applications, and are capable of a lot of power but require some work. They are dirt cheap, like $100 if you use the 20% off coupon.
Most of us here are leaving them stock for trains, so I'll touch on the basics.

The basic reliability issues are as follows:

The hardware is of poor quality(harbor freight) and the bolts stretch and don't maintain torque even in cast aluminum. I install grade 10.9 metric flange bolts in the side cover and throw the stock ones away. If you don't, the side-cover can come loose, oblong the dowel holes, and then it leaks out all the oil and it's junk.

Some of the accessory bolts may rattle loose and fall out, these engines shake a lot so I take the bolts out one at a time and blue Loctite everything. Make sure you remove the pull start cover and also Loctite the ignition coil bolts. If the coil comes loose and drops into the magnet slot in the flywheel while it's running, it can have explosive results.

At the high RPM's we run, we toss the cast iron flywheel and install a billet one. No need for regular governed use.

The gas caps on the stock tanks on many of the engines leak. Not an issue since the karts run a pulse pump and we don't use the stock tank. The all metal case Mikuni pulse pump is the most reliable in my opinion, pulsed from the intake manifold.

The muffler is pretty cheesy and can break. There is a lot to be gained in making your own or buying something else, for more quiet operation or for more power.

Myself and my fellow racers had engine failure after engine failure running some of the top synthetic oils like Mobil-1 and Castrol. Someone would lose an engine and oil the track nearly every race day. It came down to two things. One of the turns was a long right hand sweeper into a right hand hairpin that took about 12 seconds to pass through. The G's being pulled was pushing the oil into the side of the engine and starving the connecting rod. A lot of the seizures were happening after this section of track within a turn or two...about 10 seconds later. We increased our oil amount to 20oz and had less problems, but still problems...not so much seizures but a lot of metal in the oil. There was ONE guy who never had any trouble, and he was running Briggs racing oil, which turned out to be made by Amsoil and is loaded with ZINC. Even the best car oils don't have enough zinc and did not work. In a karting forum argument, I wrote Castrol and Mobil-1 about our application and their oil, and another guy wrote Pensoil, all three replied surprisingly, and said more or less "heck no", steering us to racing oils (EPA exempt, high zinc content). Since all of us have switched to a high zinc content oil of one type or another, it's a rare event for someone to lose and engine anymore and the "silver paint" in the used oil is also a thing of the past. I did have the side cover come loose and lost all my oil on the track(it was raining horribly and I didn't see it), and it went THREE laps, almost 4 minutes, before it started to bog and I realized what happened and shut it down before it seized. Engine life has gone from several races to several years for me since then.

Sources of high zinc content oil are off road use only racing oils like Amsoil and Redline, marine oils, motorcycle oils, and break in oils. Maxima's motorcycle oil is good stuff and is available(locally for me) in petroleum, blend, and full synthetic. The petroleum version works great for "stock" applications, I run it in my generator, compressors, my pickup, boats main and trolling motor, and the engine bound for my 12" gage locomotive build. It's only about $1.50 more a quart, and I seem to be able to get about double the time out of it in my equipment. My pickup see's a lot of short trips and gets the oil dirty so I don't extend my changes there.

There are a few different #'s of harbor freight engine and they are quite different inside. The #60363 is the hemi, and has a flat top piston, full open chamber cylinder head and larger "canted" valves with push on style spring retainers. These make good top end power when modified. The #69730 has a partial chamber head, dished piston, and smaller valves, but has automotive type valve spring retainers. These make better torque. Some racers put the 730 head on the 363 for alcohol as its like 13:1 compression and over 20HP, but the block has to be braced or it will blow the jug off the case!

Lastly, any of these engines need to be broken in, and put out a fair amount of metal into the oil during it. I do a 10 minute no load low-mid RPM bench test with some 5w-30 motorcycle oil, then change it. Then 15 minutes, change it. Then mount it and run it, 1/2 hour, change it again. If you use a new black plastic oil pan and wipe it out each time, you'll see the used oil clear up when it's broken in. When any of my engines are going to sit for awhile, I run a mix of 2oz seafoam, 4oz 2-stroke premix oil to a gallon of gas and run the engine until it starts to smoke and leave the carb full. Never had any problems with a carb plugging up or gumming up since.

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Re: Gas engine selections and prep

Post by makinsmoke » Wed Oct 11, 2017 9:28 pm

That's an amazing amount of information paid for through time, money and experience.

I see improvements to our hobby by extrapolating the data to our in-situ
engines whatever the make. Modern fuels and modern lubricants don't necessarily
apply to lots of off road and heritage engines. We all have a lot to take away
from this information.

I can tell you that a 1950 Willys Jeep has many of the same issues, dealing with
low or zero zinc and sulphur lubricating oils, and no lead and ethanol blend

Thanks for your efforts to document and pass on this information.


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