31 HP Vangaurd Twin eating pushrods

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  #1  
Old 11-15-16, 04:26 PM
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31 HP Vangaurd Twin eating pushrods

543477-0342...??? I believe are the numbers, don't have them with me...

It setup to run basically a turbo vacuum for a fire a flood damage restoration company.

I replaced the push rods on the left bank (left looking at it from the output shaft side) and set the lash, rotated it twice through by hand and rechecked. I got it to fire briefly before nothing...you can see the push rods through the oil fill hole and it immediately bent another rod on the exhaust side.

I have found this many times but always been able to reset as many times the rods simply fall out without damage, or replace the rod and set the clearance.
Some things I have found others have found out is:
Worn cam lobe, valve guides, compression release, (Not sure yet if it is even on this cylinder) weak valve springs.....

Just looking for any other ideas if the customer wants me to go digging into it.

He did say they replace this engine about every 4 years. It is direct drive to a compressor and huge fan upon starting/cranking.
 
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Old 11-15-16, 06:15 PM
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Cam lobes, worn valve guides, and comp release won't cause the push rods to fall out like this. You have a valve sticking, a valve guide slipping up and down in the head, or a valve seat falling out and holding the valve open. If the engine has likely overheated, the valve seat or guide slipping is probably the problem. If it has run on stale gas, the valve sticking is probably the cause.
 
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Old 11-15-16, 08:10 PM
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I mentioned valve guides, not worn, but still slipping I have seen other mention and that is still worn or it wouldn't slip..?
I was leaning to a valve sticking myself as well, bent stem or...guide hanging......?

This thing is shoe horned in the back of a panel truck with this side of the engine only a few inches from the wall and the access door does not provide good access to that cylinder.

This is basically the same engine that Grasshopper uses and we have a couple scrap ones I thought about pulling the push rods out of just in case I was in error in setting the clearance.

I also checked the clearance on the valves on the other cylinder, and they were between .005 exhaust, and .007 intake...so I went with .005 when I set the bad cylinder.

Either way the thing has to come out for me to get the head off so....


What do you think about it not having any type of PTO? I know hard on starter but , briggs also warn about engine damage when starting under a load just like having blades engaged on a mower and trying to start.....and this thing is turning a load!!!!
 
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Old 11-15-16, 08:34 PM
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Also originally the intake push rod was bent worse than the exhaust side........after replacing both were still seated in the rocker and the tappet...
 
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Old 11-15-16, 10:57 PM
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A guide can slip if it's worn or brand new. If the head gets hot enough and expands far enough, the press-fit of the guide is not so tight anymore and the guide can move with the valve. It can slide upwards towards the end of the valve stem and if it sticks there, it won't let the valve go back down when the push-rod comes up to open the valve, and then you get a bent rod. Usually it only happens on one at a time.

I was reading that the pushrods fell out without damage many times, but I see now you were saying you've seen this many times before but not meaning on this engine. If the pushrod is bending every time, it rules out valve seat and probably sticking valves. I'd say your guide came loose and is keeping the valve from opening. A sticking valve is possible, but usually they stick open, not closed, unless they are rusty. Also, it sounds like the engine is in a tight spot and probably doesn't get the cooling it needs (recirculating hot air)... which supports the guide theory. You can take the valve cover off and pop the spring off the valve and see if the guide is extending up too far from the head. Another possibility is that sometimes the guide will move the other direction and hold the valve open, the pushrod falls out, the piston comes around and slams it back shut and the guide moves back into place, the engine stalls. You put a new pushrod in, the engine runs because the guide is back in place enough to run, but the valve stem is bent from the impact of the piston and makes it want to stick, bending more pushrods. If that is the case, you still need a head because the guide will eventually move again once it heats up enough.

The engine starting under a load won't cause the pushrod problem. It is tough on the starter and could be a little harder on the engine if it's hitting really hard at low rpm before it can get up to speed (lugging), but if it's been working, it's probably okay. If its shaking hard and knocking and making slamming noises when it is starting up, the load is probably too much. Since it's on a compressor, the load probably is low at startup and increases as pressure or vacuum is developed once the engine gets to RPM.
 

Last edited by cheese; 11-15-16 at 11:16 PM.
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