gx390 honda piston rod help!

dubs27

Long story short I rode my cart a few weeks ago through some really wet woods on the way back the motor seemed to lock up.After I was pulled back. I got it to crank back up and load it's self on the trailer but it developed a knock. When I took it apart today I found the bearing bolts had backed out of the rod and was hitting the case. Should I just tighten the bolts back up or install new bearings too? Thanks in advanced

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geoffw

I would replace the rod. More than likely its damaged.

If you pull the rod cap off, youll see the condition that its in.

dubs27

Yeah I did. The rod cap is shot. The crank has some wear on it also should I replace it too?

geoffw

Chances are the crank will need to be turned. It might be more cost effective to replace it. Check with your local crankshaft shop.

Id upgrade to a billet rod with a bearing so it doesnt happen again.

dubs27

thanks Geoff I'll order it this week do you sell the crank?

sho305

Ouch, that is a major failure. I checked mine to make sure they were tight when it was new, but nothing more.

dubs27

I bought this engine used didn't check it. I guess it could be worse. I don't even see a bearing in the bearing cap? There wasn't that much metal in the oil. I've never done a motor rebuild but have done alot of research. Do I need to check the bearing clearances, When I reinstall the new rod? Should I go ahead and replace the rings also?

sho305

Stock alum rod is its own bearing. Rings are up to you, I look at the ridge on the top of the cylinder and if not there rings should still be good, otherwise now is the time usually they are not that expensive but you have to hone it some too. Try some ziinc additive or off road oil with more in it.

geoffw

Rings are cheap insurance if you can hone the block yourself.

Stock rods dont have bearings, thats why they are failure prone.

Upgrading to a Billet Rod is the best insurance you can buy.

sho305

Usually the problem with rotating things is the force increases as a square or whatever the exact formula is, that means if you turn it twice the rpm the force on it is way more than double. The rod is made for 3600 rpm on stock power and compression, it will last with that a long time and will last with other mods and stock cam even, but not much more. I read at a place that makes aftermarket parts the stock rod does not oil well at high rpm is the major issue. They said at 6K it loses its oiling and did not recommend you run 6K or more only in short bursts. The stock cam can hardly make it there.