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B & S 17.5 HP Problem

#1

G

gary8241

When I shut off the engine ( 17.5 Hp Troy Bilt mower) it of course spins a bit until it comes to a compression stroke then stops. Go to try to start again and it will not go through that compression stroke acting as if the battery was low or starter is weak. If I spin the engine back a bit so that it has a running start coming to the compression stroke it will get passed it and start. New battery and starter. Any ideas?


#2

I

ILENGINE

I would start with checking and adjusting the valve clearance, and if that doesn't fix the issue then most likely would need further checking to determine if the ACR on the camshaft is broken.


#3

S

slomo

gary8241 said:
New battery
Click to expand...
New battery means nothing. Needs to be load tested. Auto parts stores check for free.
gary8241 said:
New battery and starter.
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Save the old starter. Could be good. Take a jump pack and see if the starter spins over.

Agree check valve lash as ILENGINE said.


#4

A

Auto Doc's

Number one problem is the valve lash adjustment.

Go to a You Tube site called Teryl fixes all. He is a bit of a clown but has all the info you need about how to adjust the valves.

The next problem could be more serious and the compression relief mechanism is broken or stuck on the camshaft. This would take professional repair knowledge to correct.


#5

S

slomo

Did this get fixed and slaying some grass? OP ghosted us.


#6

G

gary8241

slomo said:
Did this get fixed and slaying some grass? OP ghosted us.
Click to expand...
Thaks for the response. Yes, I have no problem there. On advice gained on this site I have adjusted the valves but the problem persists. I guess it is the compression release on the cam. When I start the tractor have been rotating the engine counterclockwise a ways and that allows it to get enough momentum to start.


#7

A

Auto Doc's

Hi Gary 8241,

From your description, the compression release mechanism made onto the camshaft has given up. What is worse about the situation is that aftermarket cams and even new Briggs cams are unreliable.


#8

Tiger Small Engine

Tiger Small Engine

gary8241 said:
Thaks for the response. Yes, I have no problem there. On advice gained on this site I have adjusted the valves but the problem persists. I guess it is the compression release on the cam. When I start the tractor have been rotating the engine counterclockwise a ways and that allows it to get enough momentum to start.
Click to expand...
Before saying 100% for sure the compression release is the issue, I would strongly suggest the following be done:
1) charge and load test battery
2) clean all wire terminals and check for excessive voltage drop
3) check or recheck valves for proper clearance
4) check starter for proper operation
5) pull valve cover and rotate engine and watch for very subtle bump in valves, indicating that the compression release is in tact and working.

Rarely is it the compression release mechanism on camshaft that breaks.


#9

S

slomo

There are 2 TDC strokes on a 4 smoke engine.

Easier valve check is one valve pushed open out of the head, adjust OPPOSITE valve. Do this for all other valves.


#10

G

gary8241

Tiger Small Engine said:
Before saying 100% for sure the compression release is the issue, I would strongly suggest the following be done:
1) charge and load test battery
2) clean all wire terminals and check for excessive voltage drop
3) check or recheck valves for proper clearance
4) check starter for proper operation
5) pull valve cover and rotate engine and watch for very subtle bump in valves, indicating that the compression release is in tact and working.

Rarely is it the compression release mechanism on camshaft that breaks.
Click to expand...
Thanks for the advice, will try.


#11

Craftsman Garage

Craftsman Garage

gary8241 said:
On these engines, this is a very frequent problem that I have run into and it is always caused by a bad compression release
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#12

A

Auto Doc's

I have replaced a few camshafts due to a bad compression release mechanism, but most of the time owners don't want to fix them. I have 3 of them right now in my scrap mower collection.

I don't trust the replacement cams offered enough to invest the money and fix them myself. I have had too many repeat failures with these.


#13

Craftsman Garage

Craftsman Garage

They don't call them "Breaks and scrapem'" for nothing. If they break, scrap them, because they are not worth fixing because they will just break again.🤦🏼‍♂️


#14

A

Auto Doc's

I have a lot of older Briggs & Stratton engines still going strong, most are the much older flat head design.

For longevity, I gotten the best life out of Kohler engines when it comes to riders.

Honda is a close second when it comes to other power equipment.

The way emissions laws are going, they may all be scrapyard bound in the near future


#15

Hammermechanicman

Hammermechanicman

gary8241 said:
Thaks for the response. Yes, I have no problem there. On advice gained on this site I have adjusted the valves but the problem persists. I guess it is the compression release on the cam. When I start the tractor have been rotating the engine counterclockwise a ways and that allows it to get enough momentum to start.
Click to expand...
I have a couple customers with bad cams on old craftsman mowers. Not worth having me put cams in them and i showed them the turn bsckwards till it hits compression and then it will crank. They think i am some kind of magician LOL


#16

Craftsman Garage

Craftsman Garage

Craftsman Garage said:
I love those old flathead engines. One time I was able to run one of those 3 hp flat heads on a edger for about 50 hours without oil! It had an oil leak that I did not notice
Click to expand...


#17

F

Forest#2

Instead of immediately loosening the INTAKE valve adjuster and fiddling around with taking the INTAKE valve lash to minimum specs to check for compression release I just use feeler gauge under the rocker valve stem and take the lash to minimum using the gauge and check for crank through.
Saves lots of time W/O doing the actual lash adjustment at first.


#18

A

Auto Doc's

Gee! Everyone wants to sound scientific.

Keep it simple.

Pull the plug and remove the rocker cover. Rotate the engine by hand in the normal cranking rotation and watch the intake valve movement. If the compression release is working, there be a quick bump of the intake valve before it opens normally. If the Intake valve operates all in one motion just like the exhaust valve, the compression release is not operating.


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