Booins

I have an old Nitro Star 12E engine on my RS4 with overheating problems. I can run half a tank with open throttle before the engine stalls. I have noticed that the engine head smaller than the head on the newer engines today. Could this be the solution to overheating? I have also heard that running the engine richer will solve overheating problems but it hasn't worked for me. Any help on how to keep engines cool would be appreciated.

Another problem I have is the screws in the engine head are stuck. When I reinstalled the header I made sure the screws were snug but not torqued down. When I try to back out the screws the Phillips head just slips out of the screwdriver head. The screw driver only grips the screw when tightening. I know most people would tell me try a new screw driver, but I have! I have tried every screw driver I own. From small electronic screw drivers to whatever fits through the head. I have never heard of this happening to anyone else. Suggestions on how to remove the screw would be appreciated as well!

Thanks.

cbaker65

Do you let the engine cool off before trying to un screw the screws ? It helps when the engine is still hot to un screw the screws!
If that doesn't help ,then your screwed!
Best thing to do is to cut the head back to expose the head of the screws an try to get the screws out ,then try to find a new head.

1QwkSport2.5r

There is a possibility the screws in the engine although similar to Phillips head screws could in fact be JIS screws. JIS screws have a different and specific driver to install/remove them and most often a standard SAE Phillips driver will strip them. I believe the HPI FE engines were made by Toki in Japan.

As to the overheating - you're probably not rich enough on the needles or your piston/liner fit is getting loose. Usually a worn out piston fit will cause the engine to run hot, quit often, and not restart until it cools off. How are you determining it's overheating and what measurement device(s) are you using?

Booins

Your description of the engine over heating due to the piston fit is a direct match! I do believe the piston is worn but I am not looking forward to purchasing a replacement sleeve and piston. They are expensive!! Would you recommend a whole new engine instead, for double the price? After all, its a little vintage .12 with almost no parts available.
As for the screws, the weird thing I have noticed is that they don't strip when I am attempting to loosen them. The driver head just seems to slip right out. However, If I turn the driver clockwise, to tighten the screws, the driver grips the screw heads. At this point I am going to assume they are JIS screws. Luckily, I have replacement hex's on hand. I will be sure to try a JIS driver as soon I get my hands on one.

The Saylors

A trick that i learned with those darned phillips heads is this: First clamp the motor down. second get out a rubber mallet and the closest fitting driver you have. Third put a medium amount of twisting pressure on the driver (a tiny bit less pressure than it takes to make the bit jump out). Now very lightly tap the top of the while pulsing your pressure on the driver. You should be applying twist when the mallet taps the top of the driver. This is a cheater way of gently impact driving the screw. I didn't think it would work until i tried it on my ke-25 backplate screws. It worked like a champ on 3 nearly completely stripped screws in a row! Just be patient and take your time! hope this helps

Booins

Sounds promising to me! I'll be sure to give it a go and let you know how it works out. Thanks for sharing!

1QwkSport2.5r

It's always cheaper to replace the piston/liner/rod than the whole engine. If the bearings are good and the engine is otherwise in good condition, just replace the piston/liner. If the rod is worn, replace it as well. If parts are unavailable, replace the engine. Nursing a worn out engine isn't gonna work and will just waste fuel and frustrate you. That engine is hardly a barn burner, so unless it has sentimental value, getting it re-pinched or replacing the p/l is not worth it.

Booins

How can I tell if the rod is worn?

The Saylors

extra slop in the joints and any visual flat/scuffed spots. Also look for discoloration or "hot spots"

Booins

What effect does discoloration and scuffs have on the performance? I have another engine that I rebuilt and won't start. The rod is chewed up but still does its job from what I can tell. Could that be the reason it fails to start?

The Saylors

It can become a balance issue more than anything. These motors are so tiny that most vibrations are undetectable by a human without special equipment. These things can also point you to a different problem in the motor, pieces shouldn't be colliding hard enough to beat up parts, if they are then something is possibly wrong with a bearing. If a bearing is toast then the motor is likely done for unfortunately I don't know if you have ever driven a car with a motor that is on deaths door? Usually not a bit of power, cant idle, and vibrates like crazy. Although these are not four strokes they still show some of the same symptoms of their bigger cousins. On that one that wont start, did it ever run for even a min after you rebuilt it or has it been d.o.a. since day one? Just curious but some of the pistons are directional meaning that they have an asymmetrical shape on the bottom of the piston. If it goes in backwards it won't allow air and fuel to go were they need to go but that is not the case for every motor. My kyosho foxx is an example. One side of the piston is smooth while the other side has an arch on the bottom lip of the piston to accommodate the intake and exhaust ports.

Booins

The beat up rod was my fault. This was the first engine I have ever worked on and unfortunately I beat up the connecting rod trying to remove it forcefully from the crankcase. I did receive the engine dead, but the previous owner claimed it ran 10 years ago.. And from what I can tell the piston is not directional. It is a Traxxas .15 Pro.
Also, from your description of "deaths door", I think that is where the Nitro Star is at. The idle screw has to be adjusted so far to keep an idle that the clutch engages. I have to lay on the brake when I want it to "idle". The more info I keep receiving, the more I think about tossing this old engine.

Booins

Cutting into the head would seem like the last resort to me. I have also tried to back out the screws with the engine hot, but still no luck. I think I may be screwed..

Booins

I was really hoping this would work but I gave it a try with no luck. There is really NO bite with the screwdriver. I felt like I was just pounding a nail into the engine. Once I find a JIS driver this trick may come in handy...

1QwkSport2.5r

The rod is considered worn when you have more than say a .003" variance in size between the OD of the crankpin and ID of the rod bushing. In some cases, the rod AND crank need to be replaced. If you hear any metallic noises ("tink" is the sound I hear from a loose rod) when you turn the engine over, that's a good reason to measure the parts. You want to have some "slop" between the crankpin and rod bushing to allow oil to get in and lubricate it. An engine that's started right away and kept at operating temp during the run will keep the crankpin from "hammering" the rod bushing. A cold and tight engine will get the rod bushings hammered up pretty bad if constantly trying to start it. When the engine is running, the brunt of the pressure should be in the same places constantly. Bottom of the upper rod bushing and top of the lower bushing. Looking at a worn rod from an engine properly run and cared for will show shiny wear patterns in those areas. Engines with poor tolerances and/or poor treatment will show wear on the top and bottom of the rod bushings.

The Saylors

Ya cutting the head is a pretty big gamble to me but if your gunna toss the engine then i guess you could try it. If you dont know the steps to taking a nitro apart then i can see were you would feel the need use force and hurt something (i had watch a vid the first time). Those nitro's aren't crazy expensive but they certainly aren't free. It may be worth saving the hassle and just going that route. You can only try for so long before you're just wasting your time

The Saylors

You dont wanna be hammering on it hard like a nail, light tap is all you need. I know if feels like you need more ump but really the pressure should be on the driver handle. The idea is to use the hammer to take the pressure off the threads for a split second and twist in one motion. All that i could make fit was one of those tiny glasses type drivers so i was holding onto them and applying twist pressure with a pair of vice grips. So if you cant do it by hand try holding the driver with pliers or v-grips. Are JIS heads just more shallow than regular phillips? I would just file down a bit a little if thats the case lol. I have seen those screws with the dimples and never gave it any thought!

The Saylors

Oh now i see they have an inner 90 degree angle to them that makes sense why a normal set wouldn't bite correctly.

Booins

Yes they do have a 90 degree angle. But I cant find a dimple on the screw heads which identifies them as JIS. I am not sure if every JIS screw head will have a dimple? Especially older ones.. But the Phillips drivers are definitely not the right fit.

Booins

I have found some new-old stock on eBay. I can pick up the p/l/r for around $40. Do you think this would be my best option? Would it solve all of my problems? If I do purchase a new p/l would it require a break-in?

The Saylors

Yep any time you do a piston and liner they have to be re-broken in just as if the motor was new in order to seat the piston to the liner properly. Usually an other wise healthy motor will benefit greatly from this. This is always what i try first before going with a full replacement.

Booins

Before I can do anything I have to get that stuck head off... I went out on a hunt today for a JIS driver but none of the major auto/hardware stores carry them. I was told that they are considered specialty tools and hard to find. Does anyone have suggestions on where to buy them online?

The Saylors

https://www.amazon.com/s/ref=nb_sb_n...rds=jis+driver

The Saylors

Looks like that driver is a Japanese tool. The first set on amazon looks like its pretty highly rated and is pretty cheap. Does have a couple bad reviews but just about everything does but for the most part they are making people happy.
http://www.amazon.com/Hozan-JIS-4-JI...=sr_1_1&sr=8-1

1QwkSport2.5r

I personally would not bother putting $40 into an old and outdated engine. If it has nostalgic value, then sure... But honestly, I'd save the $40 and put that towards a much better quality engine that will run better and be easier to tune.