Chinese 4 stroke model camshaft repair advice

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M16mdl

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Hi there. I am new to the forum and do love model engines. I got a m16 Chinese model 4 stroke engine which I run on white gas and MMO. I am really entertained by these things. I’ve put a grand total of 36 hours of run time on this little model.
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After a nice tune on it, the camshaft has started to wear significantly. Making a big pit in the middle of the lobe.
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I need some adviceon how to fill this lobe so the valve opens enough to run right. Currently, the valves don’t open enough to let the engine rev up. It’s even at 0 clearance with the rockers.
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When you run it, it just stalls out when you give it throttle. Because the valve doesn’t Open enough to let the huge mix of air and fuel into the cylinder. Thus making it stall out.
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Ive
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tried jbweld, however the followers just cut through the JB weld. I’m thinking of some sort of weld to fill the pit that has been worn down. What do you think? The camshaft may be aluminum because of how quickly it wore.

Any questions let me know and please give me some suggestions. Thanks!
Cam issue after v Before ^
 

Chiptosser

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You should take the cam out of the engine to repair, I don't know of anything to repair the lobe in the engine.
Have the lobes built up with aluminum bronze, I would do both. Or, have it tig welded.
You will be able to file the lobes back to shape. From the looks of the lobe, I would guess the material is mild steel. You will most likely have to resurface the face of the lifters. They are most likely gulled.
 

stevehuckss396

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If I were in your shoes I would pull the cam out and have one machined using some good tool steel. It is only a 2 lobe cam so it should be somewhat of an easy job. Either machine the lobes off and make new ones to be pinned on or just make a completely new one piece camshaft.
 

minh-thanh

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I don't understand why the lobe surface is scratched everywhere, even in non-contact places
Looks like the surface is not good from the start . and not polished
 

M16mdl

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I think aluminum brazing rods would be a good start
 

M16mdl

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Maybe if you had a good base but it appears that you have some poor steel. Just bite the bullet and pull it out. Do a quality repair so you wont have to deal with it again.
I don’t have a lathe. I would love to have someone make me a stainless steel camshaft. I could give dimensions. I would also ask for some larger lobes
 

M16mdl

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Maybe if you had a good base but it appears that you have some poor steel. Just bite the bullet and pull it out. Do a quality repair so you wont have to deal with it again.
I’ll also pull the shaft out. I’ll get a caliper and measure the size. The 2 ends are smaller because they have to fit in bearing slots. I’m sure there are some good machinists here that could make me one for a reasonable price. Not that much metal since the thing is so small!
 

ajoeiam

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I’ll also pull the shaft out. I’ll get a caliper and measure the size. The 2 ends are smaller because they have to fit in bearing slots. I’m sure there are some good machinists here that could make me one for a reasonable price. Not that much metal since the thing is so small!
(Grin) Maybe not much metal but there's a bunch of time taken even in machining a small version.
Sometimes its far more time consuming to machine a smaller version that to do a larger one.
A larger version of some items allows one to use tooling that may very much speed the process.
(Not a given that smaller parts cost more but its also not a given that such are cheaper - - - its all about the time involved!!)
 

awake

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I think aluminum brazing rods would be a good start
Aluminum brazing rods would only work at all if the shaft itself is aluminum ... and if the shaft is aluminum, it is the wrong material!
 

M16mdl

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Aluminum brazing rods would only work at all if the shaft itself is aluminum ... and if the shaft is aluminum, it is the wrong material!
Well I’ve made the decision to get a new one machined. So that’s out of the question. The whole engine is in pieces at the moment and the camshaft is out.
 

Mechanicboy

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I can't understand why the cam shaft was not made of hard steel to example drill rod/silver steel. Bad selected steel as material for cam shaft who are too soft to resist wear from valve lifter. And there is not rotating valve lifter affected by cam shaft to resist wear, also the centerline of the lifters are offset slightly with respect to the cam lobes. This makes the lifters rotate as the cam turns, which helps to reduce friction and wear.

Better to make a new cam shaft of drill rod/silver steel and all surfaces (both cam lobe and valve lifters) polished to resist wear and make the lifters offset to rotate the lifters

Lobe offset.jpg
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Valvelifter.jpeg
 
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Mechanicboy

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Mechanicboy

"I can't understand why the cam shaft was not made of hard steel to example drill rod/silver steel."

Simple one word answer CHINA
Simply answer: Remnants of steel from the Chinese Cultural Revolution when people tried to produce steel from backyard foundries in their respective homes that must be used up without loss of income. ;)
 

Bazzer

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You are correct, the Chinese can make anything they desire to the highest standards but the desire is not there in consumer items like this engine being made by a start-up company where cost and availability dictates where the next meal comes from.
 

Mechanicboy

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You are correct, the Chinese can make anything they desire to the highest standards but the desire is not there in consumer items like this engine being made by a start-up company where cost and availability dictates where the next meal comes from.
As a communist would ask the buyer: What are you going to use high quality steel for?

Maybe not everyone can buy high quality materials without permits in China.

Here we had Soviet lathes and the day my former friend who worked in a machine shop ordered new gears because the old gears broke in the lathe that was produced in Chelyabinsk. He had to write the application that was sent back from the Soviet authorities and send back to Moscow to fill in what the gears were used for and what purpose etc. Such was the bureaucracy in the communist country and can also apply in communist China.
 

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