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rebuilding 17.5 B&S

12K views 22 replies 7 participants last post by  speedybmc 
#1 ·
I was given an craftsman mower with a 17.5hp single cylinder briggs and stratton. When i got the mower (last year) the engine was smoking a little. I ran it until now always checking the oil and adding if needed. Well this year it is a little worse and i want to overhaul it. I removed it from the mower and started tearing it down. I took the valves out and removed the old valve seal. Now, i don't know anything about a small engine but are the valves supposed to have slight play in them from side to side? With me holding the valves in and open just slightly i can wiggle them. Its not much but there is slight play in them. In other words they are not tight with in the valve guide. If this is ok and doesn't cause any problems i wont worry with it and continue the build.

What do i need to do to get the carbon build up from off the piston and around the valves/combustion chamber? I've heard things from oven cleaner to a wire brush. i don't want to do anything that'll hurt it.

I have not got to the bottom end yet so there may be more question on the way.
Thanks for all of your help
 
#2 ·
I dont have the specs in front of me, but the valves shouldnt be sloppy in the guides.

I take some oil, and lube the stems, stick them in the guides until they are flush with the top of the guide, and seal off the other end with my finger, and pull the valve out...it should make a little suction as you pull it out.
 
#4 ·
I have a Service Manual for your engine IF you would like a PDF copy. Address below, put in proper format and remind me, model number of engine and what you want. I think you will find that B&S has a go-no go Gage to check the valve guide but no specs. and the fix is a new head.

Walt Conner
wconner5 at fronter dot com
 
#5 ·
I think Ive seen that gauge before Walt, I think its tapered with markings on it, and there is a line that if it is at or past that line, its too big, replace the head, or ream/replace the guide.

If its got some suction, its probably not an immediate problem, ive pulled apart high hours engines with the valves wobbling all over, but ran fine, no smoke or problems....but the guides were completely shot to **** and back. Eventually, if it gets bad enough, the valve wont seat and it will burn.
 
#7 ·
Hmm thanks guys. i think I'm going to run it like they are and start saving up to get a head and valves.

Another question. Is there a way to get a little more hp out of these little engine? Like maybe porting the intake and exhaust port. A few guys i work with was wanting to do it for me and i noticed there is a slight lip of excess cast around the inside diameter of the intake port. Would porting it hurt it more than help? They just put the bug in my ear and i was curious if i could gain a little more horses out of it while i had it tore down waiting on parts.
 
#9 ·
BUT, a GOOD machine shop can make a set and shoulder them so they won't pull out of the head, a common problem on this series engine. I believe my machinist took a set for a Perkins and turned them down then reamed the inside and installed a liner to bring it into spec.

Joe
 
#10 ·
Porting really helps to allow more flow at high rpms..but these are governed engines. At full speed no load, the carb is only opening about 10% tops...and even under 100% load, the engine speed doesnt exceed 3600rpms...so porting really would not help much if anything, as the engine cant demand more air.

If it were an ungoverned engine, on a racing mower that was going to be turned up to 5000, 6000 rpms...and it was built to handle it, Port away and put in bigger valves, roller rockers, slapper cam, etc...haha
 
#14 ·
There were no bearings on the rod. But it was in good shape along with the rings. The culprit causing the smoke was a blown head gasket and possible the valves. it was sucking oil from the push rod valley. Everything else except the valves was in good shape.
 
#19 · (Edited)
Ok me and my buddy had the engine put all back together. New rings new gaskets.. i lined up the dots on the crank and cam shaft gears. Adjusted the valves and everything was timed up right. We put on the flywheel along with the key. I waited till this morning to run it and it ran a little rough for just a second and died. well next try it back fired so i knew something was off. I checked the flywheel key and it sheared it. Only thing i can think of it was not down all the way and it didnt have much on the crank part and it broke. Where do i get another flywheel key?? and how do i properly install it?

B&S site does not show a key on their parts list for my engine. I checked ebay just to check and there are a few on there and they all have the same part number 222698s. Are all the keys the same size for b&s engines

31c707-0230-e1
 
#20 ·
I only know of the one key for briggs engines, Vanguards to 2hp edger engines..same key.

The Key is only there for alignment, once the bolt/nut is torqued down, the key is just along for the ride, as the taper is what holds the timing.
 
#22 ·
Hey, speedy!

Glad you got your engine rebuilt. I tell you, these modern engines are a lot of work, sometimes! 65 ft pounds sounds like plenty to me, but 100 aught to do the trick. Just be careful not to strip those threads! Personally, I wouldn't be too anal either way and just tighten it as good as you can with a good 1.5' long or so adjustable wrench. I don't ever use a torque wrench when tightening a flywheel nut on a small engine, and haven't ever had a problem with the flywheel key. If it ran rough before it died, chances are the key might not have been installed properly to begin with. That may not have been the case, it may have just been warming up from the rebuild, but you never know with these things. Good luck to you!


-MTD
 
#23 ·
Well i replaced the key and made sure it was flush with the crankshaft end after the flywheel was put on. Then i torqued the bolt to 100ft lbs. I cut the grass today and it ran like new. During i started to hear this awful whining noise and figured the bearings in the pulley spindles are going bad so thats the next thing on the to do list.. It seems like its one thing after another.
 
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