Chinese 4 stroke model camshaft repair advice

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Majormallock

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A couple of years ago I made a Hoglet, similar looking camshaft, I used DIN 1.2210 / 115CrV3 steel hardened and tempered. It doesn't distort with the treatment and polishes up well. In the UK we call it silver steel. I used the reverse boring bar method in the vertical mill, cutting on the inside.
 

Mechanicboy

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And make the valve lifter to rotate in same time under lifting the valve lifter to keep cam shaft life lasting. Also make cam off centered to center of the valve lifter to force the valve lifter to rotate.
 

Eccentric

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I have measured the camshaft and created a drawing. The dimensions with three significant digits are actual measurements, while the ones with one significant digit are estimated. I think I will be able to create a functional part using 5/16" drill rod with hardening and tempering.

I could not discern a difference in the profiles of the two lobes so will go with a common lobe design. I do not know the direction of rotation or which is exhaust and intake lobe anyway. I measured a 100 degree separation between the lobes, I am used to seeing a bit more, but the nose radius is also larger than I have seen so I think this will allow the 100 degree lobe separation.


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I will provide another update when I start making chips.
 

Mechanicboy

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I have measured the camshaft and created a drawing. The dimensions with three significant digits are actual measurements, while the ones with one significant digit are estimated. I think I will be able to create a functional part using 5/16" drill rod with hardening and tempering.
Look at the post #16 why you need the valve lifter must be rotating in same time the cam lobe is lifting the valve lifter...
 

Eccentric

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Look at the post #16 why you need the valve lifter must be rotating in same time the cam lobe is lifting the valve lifter...
I don't disagree, however, I have been tasked with fabricating a replacement hardened camshaft. I do not have the engine with its lifters and so do not feel I would be able to redesign the lifter/camshaft geometry to incorporate the desired valve lifter rotation you describe.
 

M16mdl

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I don't disagree, however, I have been tasked with fabricating a replacement hardened camshaft. I do not have the engine with its lifters and so do not feel I would be able to redesign the lifter/camshaft geometry to incorporate the desired valve lifter rotation you describe.
The lifters on the original camshaft (while being small), would actually rotate. So if you follow the same design you should be fine. I needed to send the lifters but was in a rush. I will see if I can send you some form of dimensions for the lifters and I could sand them down to size if too big.
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Also, the lifters need to have more lift than what’s on that shaft (in the non worn spots) to open the valves more. The engine always needs the valves in perfect adjustment, otherwise it will not rev up and flow nice. So the lift that they open must be more than stock
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the current lift is insufficient for this model. Something like the stated (future) with more lift to open the valves up more would open the engine up and let it run like it should. Let me know what you think. Thanks
 
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Mechanicboy

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The lifters on the original camshaft (while being small), would actually rotate.
After you has received the cam shaft and valve lifters, hone carefully on the cam where the green area is showed to a bit angle to not have contact with the lifter and check the lifter is really rotating each time the lifter is lifting by cam when the engine is running. The lifter need the large disc than to cover the wide of the cam lobe to make less wear on cam and in same time rotate the lifter.
off side.jpg
 

Eccentric

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This is an update on the progress machining the new Chinese camshaft. It took me a couple of days to create and test the G code program. I cut several cam profiles from wooden dowel before I used the drill rod (silver steel) seen below. A couple of things of note in the machining: the 1/8" ball end mill is offset to the side by .125" so the edge of the tool does most of the cutting and not the center of the tool. Also the direction of rotation of the work piece is clockwise from this view. This is done so the cutting of the fresh metal is brought to bear on the side of the cutter instead of the bottom.

1638045567098.png

Second Roughing Pass

I am removing .025" of material both axially and radially on each pass, the step-over is .025" for the roughing passes and .0075" for the finishing pass. There are three roughing passes and a single finishing pass.

1638045598065.png

Half way through the final finishing pass



Below are a couple of shots of the completed cam lobe machining.

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The lobe dimensions are spot on.

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The work piece, collet and collet chuck will be mounted in the lathe and the balance of the machining will be performed. Then some finishing work, polishing, and hardening.
 

M16mdl

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This is an update on the progress machining the new Chinese camshaft. It took me a couple of days to create and test the G code program. I cut several cam profiles from wooden dowel before I used the drill rod (silver steel) seen below. A couple of things of note in the machining: the 1/8" ball end mill is offset to the side by .125" so the edge of the tool does most of the cutting and not the center of the tool. Also the direction of rotation of the work piece is clockwise from this view. This is done so the cutting of the fresh metal is brought to bear on the side of the cutter instead of the bottom.

View attachment 131395
Second Roughing Pass

I am removing .025" of material both axially and radially on each pass, the step-over is .025" for the roughing passes and .0075" for the finishing pass. There are three roughing passes and a single finishing pass.

View attachment 131396
Half way through the final finishing pass



Below are a couple of shots of the completed cam lobe machining.

View attachment 131397
The lobe dimensions are spot on.

View attachment 131398


The work piece, collet and collet chuck will be mounted in the lathe and the balance of the machining will be performed. Then some finishing work, polishing, and hardening.
Great job! Love seeing the progress :)
 

Eccentric

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The final step is to heat treat. I take the camshaft and wrap it up in wire as shown below, I then make a slurry of isopropyl alcohol and boric acid. I heat the camshaft and dip it in the slurry, reheating and dipping a few times until I have a nice coating of boric acid on the part. Then I heat it to bright red hot and quench in oil.

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Below is the part after quench, it is free of scale. I boil up some water and rinse off the boric acid.

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Finally I do a file scratch test. The file glides off the new part without making a mark, but when I do the same test on the old one, the file cuts easily. This notch is indicated by the red circle below on the old part.

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Well that's it. I'll call 'er done.

As Joe Pie says, "I'm out."
 

jimmor49

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The final step is to heat treat. I take the camshaft and wrap it up in wire as shown below, I then make a slurry of isopropyl alcohol and boric acid. I heat the camshaft and dip it in the slurry, reheating and dipping a few times until I have a nice coating of boric acid on the part. Then I heat it to bright red hot and quench in oil.

View attachment 131431

Below is the part after quench, it is free of scale. I boil up some water and rinse off the boric acid.

View attachment 131432

Finally I do a file scratch test. The file glides off the new part without making a mark, but when I do the same test on the old one, the file cuts easily. This notch is indicated by the red circle below on the old part.

View attachment 131433

View attachment 131434

Well that's it. I'll call 'er done.

As Joe Pie says, "I'm out."
Did you temper after heat treatment?
 

Eccentric

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Yes, I did temper after heat treat, but just a bit, a very light straw. I am willing to get a bit more hardness and live with a bit more brittleness. A camshaft does not experience the "striking" blows that a cutter does so I figured this was a good balance.
 

Zeb

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Camshaft lobes and lifters typically have the highest contact forces on an engine. It is said in legends that oil turns to the consistency of nylon under those pressures. That run time seems high for that little engine, so not too shabby. I'd probably be cleaning those lobes before each run and applying a thin coat of assembly lube.

I almost started out with a Chinese knockoff on my first but went with a US made casting kit instead. I think if I had no previous exposure, I'd do what you did M16mdl. Running it til it broke would provide one or two problems to solve at a time, as is the case here.

Now I'm all over supporting casting kits made in 'Murica and Blighty, even with the price. That casting grain with a machine finish is delicious. Like that warm analog glow from my record player during Christmas season...or something like that.
 

mrehmus

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I have a friend who bought an engine and then started making a part and replacing it on the engine. By the time all the parts were replaced, he was a fairly good engine builder and went on to build many engines.
 
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