Adjust valves?

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  #1  
Old 05-12-05, 04:10 PM
Dawg
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Adjust valves?

I have a briggs and stratton 18 hp twin cylinder. It cranks hard, especially when hot although spins freely when plugs are removed. I think I need to adjust the valves but I cannot figure out exactly where or how?
model 422707
type 1510

I have removed the front cover so that I can see the valve stems and springs but I can't see anywhere there to make any adjustments. Am I in the wrong place? I have not worked on small engines before, although I have built quite a few small block chevy's in my youth, so I do understand the how tos of adjusting valves. I am just in strange territory and am pretty lost now.
Any help is greatly appreciated.
 
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Old 05-12-05, 05:01 PM
Dawg
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Uh oh. I may have figured out the valve adjustment problem. Is it that there is no adjusting the valves on this engine?
If so, as to the hard cranking part, as the engine revolves, it gets extremely tight at about tdc. When I say tight, I mean the starter will not even rotate it past that point alone, I can force it by hand but its difficult. Yet, as I said, with the plugs out, it spins freely.
 
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Old 05-13-05, 12:26 AM
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Hello Dawg!

There is no adjuster for the valves. The only way to adjust them is to remove them and grind the stem. On an L engine like this, the way the valves wear makes the clearance less. If the clearance gets off far enough to affect cranking, it will affect it in an opposite manner than what you describe. (It will actually get easier to turn, not harder).

On this engine, there is a lot required of that little starter. The starter wears the top bushing on the end cap until it walks away from the ring gear enough to start putting a lot of sideways force on the armature, and it often forces the armature into the field magnets on the inside of the starter case. Replacement of the end cap or the bushing in it usually fixes the problem. I would also suggest removing the armature, sand the copper commutator contacts with 180 or finer sandpaper (enough to shine it back up), clean the junk out from the grooves between each contact with a knife, and use white lube sparingly on the top and bottom bushings. Replace the nylon bendix gear if needed.

This isn't as hard of a job as it may sound. If you need help, we'll be here.
 
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Old 05-13-05, 04:08 AM
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If, due to wear on the tappet(s) or cam lobes, you may have excessive valve clearances then the difficult cranking could be due to the compression release not operating properly and causing high compression on the compresson stroke of the engine. Something to think about.
 
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Old 05-14-05, 03:36 AM
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True! Have you seen that happen on L head engines? Not doubting, just wondering because I haven't run into that scenario before. The only times I've had to make valve clearance adjustments on L heads was when the valve seated so far into the seat that the stem was too long. I'll keep that in the back of my mind though...especially if you've seen it on occasion.
 
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Old 05-14-05, 09:51 AM
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Not many at all, perhaps less than 2% of the hundreds of opposed twins we've serviced over the years. It's just that these engines have an unusually high compression ratio and your average lawn tractor battery doesn't have the guts to turn them over. Then you add more compression by way of carbon buildup in the combustion chamber over time and it gets worse. But it still is something to consider.
 
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Old 05-16-05, 08:06 AM
Dawg
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Wow, thank you cheez (and others) for the help. I would never have considered that starter. I put a new, not rebuilt, one one two years ago and would have thought it would be trouble free for at least 4 or 5 years. I did what you suggested, (cleaned the armature and greased the caps) and it spins much better now.
My only problem was getting that #$%# brushes held in place till I got the armature in. I know there has to be some simple trick to it, but I had to do it the hard way. I need two more fingers on each hand and two more hands too. LOL
 
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Old 05-16-05, 11:06 PM
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Glad you got it! Thanks for the update!
 
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