# 15.5 Hp backfire



## snprnut (Jun 19, 2005)

This is my first post :thumbsup: I'm working on a 15.5 hp Craftsman tractor for a friend. He told me the original owner sheared the flywheel key, put in a new one, then parked it for a year.
So he asked if I could get her up and running again. I started it up on friday, it ran like crap. Backfire through carb, muffler was full of gas after I shut it off, then I removed the valve cover to check rocker arms, and they are loose as hell! I'm guessing something broke when he sheared that key. I checked the key today, and its ok. I cant believe that this engine ( 28N707 0173-01 9608052D B&S OHV) takes the same key as a 3.5hp B&S!
While I'm waiting for my repair manual to arrive, any thoughts on my next move?
Thanx everyone,
snprnut :roll:


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## scrench (Dec 8, 2004)

first things first you are going to have to get the carburator lined out going to have to clean verry verry good change the needle valve get it to stop the flooding , then set the valves i'm pretty sure that there should be two small round caps that set on top of the valve stem between the rocker arm and the valve make sure they are there you might look arround in the bottom of the head or valve cover , briggs only uses 2 different flywheel keys one for points type and one magnatron type or" solid state " but do look and make sure that your engine does or does not have the little caps if it is suppose to have them and they are not anywhere to be found chances are that one or both might be in the sump ( oil pan ) and could get in the oil slinger that is also the governor and could cause more severe damage but im sure there are a few out there that have one floating arround in the pan just set the valves and get the carburator lined out and you will have a good engine but i always check everything that someone has touched and make sure it is up to par air gap plug gap right key , bolt holding flywheel or starter clutch ,,,ect ,,,


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## snprnut (Jun 19, 2005)

*found a problem....*

If I remember correctly, these are supposed to be straight...(see attachments) also thanks scrench for replying to my post :thumbsup:


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## scrench (Dec 8, 2004)

there is a reason that happened something wrong verry wrong


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## scrench (Dec 8, 2004)

a reason that happened something wrong verry wrong



someone might have way overtightened the rocker arm and valve came into contact with the piston or if the valve is seized to the guide.. i would say that due to the engine shearing the flywheel key it might have a broken rod but there is something wrong one way or another if the valve hit the piston hard enough to bend the push rod that bad i would say the valve is going to be bent or the piston is going to be junk it will cause the ring land to smash into the ring or rings ,,, and cause all kinds of trouble , if it were me working on that engine i would take it off and disassemble and check it out or @ least the head off and make sure do it right the first time that is why its backfireing the valve is hung open that looks like the intake pushrod


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## snprnut (Jun 19, 2005)

yep, its the intake pushrod. and I went out to check for the caps on the end of the valve stems, and only the intake had one. So I guess the exhaust cap is gone or inside the crankcase


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## snprnut (Jun 19, 2005)

*15.5 Hp backfire cont.*

I removed the cylinder head tonight off of this 15.5 briggs, and it didnt look too bad. The valves are ok, the piston is ok, and I found the other valve stem cap. It was right under the intake valve spring..these are the pics of both valves, pics are horrible I know..
I'm going to clean them up, clean the head, and put 2 new pushrods, head gasket and seals . Put it back on, and see what happens...


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## scrench (Dec 8, 2004)

hard to tell by the pix but looks like you need to clean the valve stems might get some binding if they have any build up on them .. do they slide in the guide pretty easy ?


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## snprnut (Jun 19, 2005)

yep, they do. the valves are pretty coated with carbon, but thats nothing. no cracks, or chips. i'm bringing them to work to clean up, then tomorrow bring in the head for cleaning. just hope my Briggs OHV book gets here soon so i can adjust the valves correctly.


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## snprnut (Jun 19, 2005)

*Finally Finished 15.5 OHV!*

Well, my project with the B&S 15.5 hp is finally over. Between waiting for parts, and time to work on it, this one is in the can. I just drove it today with the deck on, everything's working ( knock wood ) The motor runs great! Not a skip. Onto the next project. :thumbsup:


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