Honda GX620 Cam Question

[1nmartin]

Hello all, new here.

I was recently given a go kart with a GX620 on it. Got the kart home and threw a battery on it and was able to get it to run easily. Then I noticed it was pouring oil out from behind the flywheel. Closer examination revealed that the main bearing on that side was trashed as the end of the crank could flop around way more than it should. So I pulled the engine off the kart and proceeded to open it up. Looks pretty good inside. Upon inspection of the camshaft I found the two lobes for the exhaust valves had a rough surface, as well as the corresponding lifters. I'm wondering if this is caused by the compression release mechanism somehow as the little buttons have a similar rough surface finish. Maybe it got stuck on? The lobes don't look to be worn down too much (compared to the intake lobes). This evidently is an older model of this engine (QDF spec), not the one that uses the 50 dollar cam that's all over the internet. If it was as simple as a 50 dollar cam and new lifters I'd be all over it. A new cam for this model is about $275 which is more than I really want to spend on it.

I wondering if
1. there is a cheaper alternative to a new honda cam? will a predator 670 cam fit this engine?

2. Could this cam just be polished and reused if too much material hasn't been worn away? How would I tell if this is an option?

3. Is there any disadvantage to removing the compression release mech from the cam if it is reusable? The governor arm had already been taken off so I plan to get the governor guts out of the engine and it seems like the compression release mechanism is just more parts that could potentially come loose and screw something up inside the engine. I will only be starting with the electric start as my engine doesn't have a pull start.

Thanks in advance.

 

[anickode]

1. Even if fixing your engine costs a few hundred bucks, that's still cheaper than a predator 670 and you have an all-around better engine. Honda or mild performance cam is your best bet. Predator is unlikely to fit, though ai don't know for sure.

2. If the cam is just a little scored and can be buffed smooth without removing much (any) metal, go for it. A good shop might also be able to tighten weld any damage and grind and polish the cam back to its original profile.

3. Removing the compression release is a good way to burn up starter motors IMO.

 

[65ShelbyClone]

Upon inspection of the camshaft I found the two lobes for the exhaust valves had a rough surface, as well as the corresponding lifters.

How rough is "rough?" Photos?

A new cam for this model is about $275 which is more than I really want to spend on it.

I'm finding new aftermarket GX620 cams for less than $50.

 

[KartFab]

How rough is "rough?" Photos?



I'm finding new aftermarket GX620 cams for less than $50.

there is the U series and the K series of gx610/620 engines. the U series are older and have the expensive cam. The K series have cams that were cloned and are cheap.

I ended up parting out my old U series and selling the parts on ebay because of this exact issue. Cam gear broke and grenaded the cam and governor balls? in the engine. Luckily i found 3 K series engines for $100, two were seized, and one was 'shot' because the cam was broken. I got all three of them to work after spending some $$ on 'cloned' parts.

 

[65ShelbyClone]

What's the difference between them?

 

[KartFab]

What's the difference between them?

Cam intake valve covers carb exhaust, not sure about the rest.

 

[1nmartin]

Thanks to all who have offered advice so far.

I took some pics of the cam and lifters today.

I also took to the cam lobes with a micrometer. It seems like the two exhaust lobes may be worn down a fair amount (compared to the intakes anyways)

I measured the diameter of the non lifting area and then to the highest point on the lobe and found the difference and I assume this is the "lift"

All four measured .950 on the non-lobed portions. The two intake lobes measured 1.175 for a lift of about .225 and they appear to be in good condition. #1 exhaust measured 1.135 for a lift of .185 and #2 exhaust was 1.115 for a lift of .165.

I figure that there may be a difference in spec between intake and exhaust, but that there shouldn't be that much difference between the two exhaust lobes.

I'm guessing at this point my only options are
1.to take the cam and have it welded and reground
2. or just bite the bullet and shell out the cash for a new cam.

Any advice is appreciated.

 

[anickode]

It doesn't even look that bad in the picture. You might even be able to dress that up with a fine scotchbrite roloc disc followed by a buffing wheel and some good buffing compound.

It's hard to guess, especially from a picture, if it has worn through the case hardening. If it hasn't, and you can polish it up, you could get a good long life out of it still. If it has, you'd still be able to run it for a while.