HF 79cc cam shim?

[atombikes]

HF 79cc cam noise?

This weekend I tore my engine apart to tap the new oil filler, remove the governor and the low oil sensor. Everything went great using AGKs excellent 99cc teardown guide (it's basically the same engine.

Re-assembled everything and re-installed it on bike, THEN I noticed that there is a loud clicking/popping noise right after TDC on each revolution. I re-adjusted the valve lash, as I had to remove the cam to get access to the low oil sensor.

Removed the engine from the bike and removed the valve cover. You can clearly see the one valve open and shut, then the other. Then right after the second, the second valve pops open and then snaps shut.

So I remove the side cover. It seems that the cam is able to move side/side and this might be causing this issue. When I look at the side cover, there is a boss with an indentation to carry the one side of the cam shaft. But there is nothing down in the recess of the boss, seems like there should be a thrust washer or something to keep the camshaft from moving side to side?

video showing the snapping noise:

https://plus.google.com/u/0/photos/yourphotos?partnerid=gplp0&pid=5919063916305737650&oid=110437225478757263348

and photo of the side cover removed:

Any thoughts/ideas?

I checked the assy diagram in the owners manual and do not see a washer in that boss in the side plate that retains the camshaft. But I did notice that the two pushrods are listed as two separate parts, even though they look identical. Could I have the reversed? They look mirror image.

Also, I just noticed that the entire crankshaft has about 1/8" lateral play (side to side). Is this normal, and if not, how do I tighten that up?

 

[atombikes]

I got a PM from member AGK last night on this topic and felt it was important to post this information back on this thread as it may be useful to others in the future. Special thanks to AGK for the very useful 79cc governor removal and 99cc Predator build guide available on their website (I used both and thy're really good with pictures)

https://www.affordablegokarts.com/79cc-harbor-freight-govenor-removal.php

https://www.affordablegokarts.com/99cc-predator.php

and also for the following, which I believe addresses all of my questions above:

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"Just wanted to let you know these camshafts have a decompression device on them. Take a look at your cam and you should see a pin or a tab that sticks out beyond the exhaust lobe. There usually is a spring loaded lever mechanism attached as well.

When you pull start the engine that tab or pin will bump open the exhaust valve which releases some compression. Once the engine starts the spring loaded decompression device will swing out of the way and will no longer bump open the exhaust valve.

Take a look at it. This might be one of the issues you are having. It's normal.

There is a good amount of side to side play in the camshafts. There is not a shim for the cam.

The crankshaft should have a little side play but 1/8" is a bit much. When you torque down the side cover you should be able to move the crank side to side just a hair.

The pushrods are the same. You can't mix them up."

 

[scotto-]

The crankshaft should have a little side play but 1/8" is a bit much. When you torque down the side cover you should be able to move the crank side to side just a hair.
The pushrods are the same. You can't mix them up."

Yes, 1/8" is a lot of end play. One way I tighten this up is to leave the paper gasket out and use a recommended crank case sealer such as Three Bond or Hondabond 4. And you can also find shims for the crank that will also help with some of that slop in your end play.

 

[culvercityclassic]

That's good information you posted. I have never had any issues with the cams. I just had one reground for a race motor. The one picture shows the compression release pin, the other shows some added spot welds to hold the mechanism for the CR together.