18 hp briggs intek cam problem?

Geo-TH,In · Oct 31, 2013

Helping a friend get his mower running. I think he has a bad cam. I put my 400 cca battery in mower. Starter won't spin motor over. Took spark plug out; motor spinns just fine. I checked exhaust valve. It was set at .006. I set it to .004. When I turn motor over by hand, shouldn't the exhaust valve open for a moment during the compression stroke, exhaust valve becomes the decompression valve? Well it doesn't. So, I decided to put spark plug in only half way allowing some compression to escape past the plug threads.
It spins over and starts just like it should.

I'm thinking it has a bad cam? Anyone have cam problems with the 18 hp single cylinder briggs? Anyone have experience changing the cam? Any ideas on what to try without taking engine apart?

Perhaps I'll drain the oil and see if there is a spring or something there.

I also posted this on tractor talk. No real good ideas from there.

George

JT Britt · Oct 31, 2013

George i believe you have to set the valves just before or after TDC if i remember correctly.Seems like i hand a pencil marked to use as a gauge.Deere had a measurement to go by but i cant remember.

joe csuti · Nov 1, 2013

You should be good with the .004" setting,I don't know how you set clearance on rocker,on the intek single cyl eng the valves are set with the piston PAST TDC & 1/4" into it's downward travel AFTER TDC,try setting valve(s) this way & see if that cures problem.if not I would say acr not working or acr cam worn.the valve timing on these eng is very close,if you set valve at TDC the valve tappet may have been sitting on acr cam,this will allow exh valve to close too early when cranking eng & putting full compression load on starter & starter will stall.

Geo-TH,In · Nov 1, 2013

JT and Joe, I'll try before and after. Let you know what I find.
All I know is the exhaust valve should open and close on compression stroke. That should be easy to see.
Thanks. Hope it works.
george

Bret4207 · Nov 1, 2013

Also, check all the wiring on the starter. Corrosion will make a good starter seem weak sometimes. Had that problem several times. Pull the starter, clean everything up and try it.

Geo-TH,In · Nov 1, 2013

Definately a bad cam. Parts store said it's a commom problem. Cam and gasket $150. Friend is going to buy a used mower and not fix this one.

No adjustment will help this problem.

Thanks to all.
George

DelMN · Dec 16, 2013

My guess is that it is the decompression mechanism on the cam. This is usually a spring loaded device that has weights on it and it functions somewhat like a governor does. It holds the exhaust valve open at cranking speed and when the engine is running the weights spread out and shut down the compression relief. The cam is probably good but the spring has either broken or has come off the mounting posts. It is not too big of a deal to dis-assemble to get at it. Side cover, valve cover, back off the rockers to relieve tension on the valves. Then you can slide the cam out and check.

18 hp briggs intek cam problem?

Geo-TH,In

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JT Britt

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joe csuti

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Geo-TH,In

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Bret4207

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Geo-TH,In

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DelMN

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