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Re-assembled Honda gx390 clone knocks


Drosner's Avatar
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07-04-14, 02:11 PM   #1  
Re-assembled Honda gx390 clone knocks

Hi All

My generator was leaking gas And after sme quick research saw it was a common problem that required a basic carb cleaning. After I did that and turn on the fuel line no more leak. Then I went to start it and I could only pull the starter chord slightly until it was stuck. Took off the recoil assembly and fan and tried to use a large wrench to turn the flywheel that way - no go. It would turn about 180 in each direction.

Figured something inside the engine must have broken due to gas getting into the engine via the carb problem? So I figured it was a good time to learn how to break down an engine.

The short of it is that after I took out the balancer, cam, and removed the head I saw nothing wrong whatsoever - as far as I could tell. I figured something got stuck for some reason and taking it apart resolved it. Only thing I could maybe see was tha one of the lifter rods was a little bent. I replaced both lifters/tappets and the rods since I didn't know to label them before I took them out.

Now the problem.....when I put the engine back together and pull the chord to rotate the engine I hear a knocking sound inside. If I remove the exhaust lifter rod the knocking stops. Then I removed the crank cover and wanted to see if I could pinpoint the problem exactly. With the lifter rods all back in place and the cover off i think the knock happens when the exhaust cam hits the lifter. I also sometimes get a bit of resistance when that happens and have to pull the chord a bit harder to get it around.

First time taking apart an engine so scratching my head as to how to resolve. Bad valve, bad spring, bad something else?

Thanks!

 
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cheese's Avatar
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07-04-14, 09:30 PM   #2  
Can you manually push the valve and it open and snap back closed? It may be stuck in the guide. The lifter should not really have enough clearance to hit the cam lobe, it should just about ride on it. .005" clearance or so.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
Drosner's Avatar
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07-05-14, 08:14 AM   #3  
It takes quite a bit of effort for me to push either of the valves down. I can just barely do it with my fingers and hold it for a second. I did have the head off and as far as I could tell the valves looked fine from the outside. I can turn the engine and see the rockers open the valves so I know they are not completely stuck.

It's a Chinese clone - locin 390g - and I ordered new lifters and push rods for a honda gx390. By my eye the parts look the same as what I replaced but perhaps there is a difference and that is causing the lifter and cams not to operate smoothly?

So from the last message I should assume that the lifters should always be close to or in contact with the cam lobes the throughout the entire rotation?

Thanks for helping a novice mechanic!

 
cheese's Avatar
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07-05-14, 08:32 AM   #4  
They should be touching the cam lobes all the time. At the loosest point in rotation (at the back of the cam lobe) there should be about the clearance of the thickness of a dollar bill. That's it.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
Drosner's Avatar
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07-05-14, 08:40 AM   #5  
Ok let me crack the engine back pie and check it again. Should the valve springs be relatively easy to push in or should it take some effort. I'm probably going to take the head off and then the valves to inspect just in case.

Something kept the engine from turning until I opened it up - and I suspect it had something to do with the valves....

 
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07-05-14, 03:42 PM   #6  
It could have been gasoline in the cylinder hydrolocking it. The exhaust valve would have hit the solid fuel fill and the cam would have forced the valve into it with the pushrod, bending it.

Did you put a new pushrod in it or use the old one?

 
cheese's Avatar
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07-05-14, 08:42 PM   #7  
You don't have to open it to check the clearance, just check it at the other end where the rocker arm hits the valve.


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07-07-14, 01:20 PM   #8  
Thos engines will sound like knocking when you pull the cord but when you put fresh oil in it and run it it runs quiet.

 
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07-07-14, 02:26 PM   #9  
I confirmed the 'knock' is because there is too much clearance at the lifter...

So i have the engine open anyway so i could see exactly what is happening. If the rocker is too lose the lifter doesn't ride on the cam the whole time and kinda "hits" the cam when i turn it around. However, if i tighten the rocker closer to the spec it seems like it takes a good amount of effort to push it through. So i figure the valve must be a little bit out of wack if it is taking the cam too much effort to push the valve open.

I can just barely push down on the spring/valve top to push the valve open. I have no idea how much force it should take. So i opened it up and sprayed in some penetrating oil and the valve seems to move a little bit easier. I assume no harm in penentrating oil in the valve shaft of the exahust right?

Last basic question for this newbie as i attempt to put it all back together. I have 2 small caps that go on top of the spring and under the rocker arm. I believe these are the rotator caps. Some people have told me i should only have one on the exhaust side and not on both valves - i have it on both. These caps are pretty much free floating on top of the valve where the rocker hits it. In other words they aren't held in place in any way - i can just reach in and pull them out.

Is this the way they are intended? Just wondering if these aren't installed correctly that could cause this to be out of wack and part of my problem.

This is a Honda GX390 clone...389cc...

 
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