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Briggs & Stratton 17 HP I/C won't crank:

16 years ago

Hey a buddy brought me his Craftsman lawn tractor to look at since it won't crank. The engine is a B&S 17hp I/C OHV single. The starter rotates the engine until the compression stroke and then all you hear is the starter straining. I changed out the battery, starter motor, oil, set the valve clearance yet the engine will not rotate through a complete cycle on its own, as if too much compression. It rotates fine with the plug out. Any ideas?

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Comments (13)

bill_kapaun
16 years ago
Did you set the valve clearance with the piston 1/4" PAST TDC?
bushleague
Original Author
16 years ago
I set the valves with one valve open, one valve closed, then vice-versa. How do I accurately measure the piston 1/4" past TDC? Thanks!
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If your confident on what you have done so far, you may need to replace the camshaft. It does happen occasionally. If you take a known good battery with good jumper cables put the + lead to the starter leg and momentarily ground the other cable directly to the block or starter housing and you have the same results at least you would know something outside the engine is causing the no crank. (DO this safely as it will spark and will ignite fuel) Did the engine blow blue smoke before this? I wouldn't call it impossible for excessive carbon to build up in the head. These take out their share of headgaskets. You also weren't specific on what you installed for parts IE size of battery, new B&S starter or aftermarket?
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"My question is this: would the improper lash of the valves cause the starter to burn up (I replaced the starter last year in my quest)? I am going to take the starter to get it checked this afternoon, but I am wondering if this is a possibility." Yah, well actually what causes the starter to burn out is holding the key to start position too long when the starter is not turning over. Never hold the key on longer than 3 - 4 seconds without it turning over. That doesn't sound like long, count one thousand one, etc., longer than you think. Did you remove the spark plug to see if the cylinder is filled with gasoline from leaking carb needle and thus hydro locked? It shouldn't need valve adjustment already if properly done before. Walt Conner
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Very good possibility that a connecting rod has transferred metal to the crankshaft from lack of lubrication. IF the crankshaft is not scored, you may be able to repair the engine but you will have to tear it down to tell. Even if you get it to turn over it will likely throw the rod very soon doing more damage. There will be an inspection plate in the back of the engine held by 4 bolts, you can remove that and get an idea of the condition, remove the rod caps. New oil sure as heck is not going to fix it. Walt Conner
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machiem
16 years ago
Find TDC and then rotate until the piston drops 1/4". Use a straw, screw driver, chopstick or whatever you want in the spark plug hole to measure a 1/4" drop in the piston. Then set the valves.
rowdy235
16 years ago
one thing- could it be that the battery wires have corroded inside the wires and now are not transferring the power well? do a resistance test, and replace if in doubt. Just a thought
bushleague
Original Author
16 years ago
I set the valves 1/4" past tdc using a scale. Actually, they were spot-on at .003". The engine still has mad compression; I can barely rotate it by hand. I'll dig deeper into the starting system, battery cables and perhaps swap a starter from an I/C 20hp twin that I have here (more torque). We'll find it.
deeredoctor
16 years ago
If the Int is set at .003 and the Exh at .005 1/4 inch drop past TDC, then most likely you have a bad cam, being the compression is high. Remember looking at the head with the cover off, the intake is the bottom valve and exhaust is the top valve.

Briggs changed the cam design for the 18's and 18.5's too, if memory serves. Make sure/verify battery cable clean/tight connections at both ends both positive and negative. Also include any engine grounds.

Briggs doesn't publish a spec for compression on these engines.
arichard21
16 years ago
This sounds like the EXACT problem I have. JD dealer says it is the valves.
walt2002
16 years ago
The most common cause of this is valves needing adjusting as said above, however, here is a fair number of these engines put out that had soft cam lobes which wore down giving the exact same symptoms as valves needing adjusted. when you adjust the valves, note the amount of lift, movement, of each valve.

Walt Conner
bushleague
Original Author
16 years ago
Well I did set the valves once again, hooked up my commercial charger to the battery, and she roared to life! I have another Briggs 17 I/C OHV that was a pull with a broken connecting rod. I found a small spring at the bottom of the crankcase which was part of the unloader on the camshaft. I robbed some parts from a 14.5 and have a rotating assembly. I'll let you know how this one goes. Thanks again for all of your replies.
bill_kapaun
16 years ago
"I set the valves with one valve open, one valve closed, then vice-versa. How do I accurately measure the piston 1/4" past TDC? Thanks!"

They should both be closed.
christopherson
13 years ago
i haven't opened it up yet but what does it take to adjust the valves?
Randysnotin
12 years ago
Not by the book valve ajustment (.25 inch past TDC)but it worked for me when by the book didnt. Watch video.
Now my tractor turns over easy.

Here is a link that might be useful: valve Ajustment
backyardbob
12 years ago
Hey guys like to add my 2 cents and maybe get some help. Mine is the 18hp ohc,wont turn thru the comp stroke with a known good battery,starter good and all connections good,set the valves at .004 1/4" past tdc. I understand you should see a slight decompression coming off the cam just b4 tdc. I have no movement in the pushrods whatsoever. Suspecting bad cam. How do I get to that? Anyone know where I can access a disassembly/shop manual? Im kind of over my head here. Doing favor for my neighbor. He says go for it but I would like some kind of instrucions. Thnx

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