Briggs Low Compression after Rebuild

[stoshzack]

Hi All -

I have an old Briggs and Stratton engine on my Toro Wheel Horse 210-5 (circa early 1990s). Trying to keep it alive. The mower wouldn't start, so I checked compression. I had a 0 psi reading, so I pulled the engine and rebuilt it (including new valves, piston head, and rings). [It turned out to be an intake valve return spring coming loose, but I rebuilt the whole thing anyway.] The cylinder bore looked good and I did not see any scoring. Tried compression on it after the rebuild and got 90 psi (which was good). Started it up (there was some smoke) and tried to fine tune the carb. Went back to work on it today and it would not start. I got a 60 psi reading on compression today. Unsure why compression would drop? Anyone have a good place to start looking before I tear the whole thing apart? I am thinking maybe the valves again.

Any help is greatly appreciated.

 

[Hammermechanicman]

Either valves or rings. Did you deglaze the cylinder with a hone? Did you lap in the valves? What did you set the lash at?
A leakdown tester would tell you where the problem is.

 

[Fish]

Put up your engine's model numbers.

 

[stoshzack]

Put up your engine's model numbers.

Model number is 257707-0123-01

 

[stoshzack]

Either valves or rings. Did you deglaze the cylinder with a hone? Did you lap in the valves? What did you set the lash at?
A leakdown tester would tell you where the problem is.

I did deglaze slightly with a hone. It is an iron coated aluminum bore. I found conflicting information on whether I should hone or not.

I did lap the valves. I set lash at 0.25 after TDC. Intake at 0.006, exhaust at 0.010

 

[Tinkerer200]

I did deglaze slightly with a hone. It is an iron coated aluminum bore. I found conflicting information on whether I should hone or not.

I did lap the valves. I set lash at 0.25 after TDC. Intake at 0.006, exhaust at 0.010

Never heard of "iron coated aluminum bore". I suspect it is aluminum bore, most 25 series were, and you used the wrong rings and aluminum bore is now scored to pieces. Aluminum bore has special coating which hone quickly destroys also.
Walt Conner

 

[Scrubcadet10]

quick way to check the bore material is with a magnet, if it pulls it or sticks to it, Cast iron bore, if not, aluminum.
OP, does the engine have the letters "I/C" on it anywhere?

 

[slomo]

Page 10 has some great info.

Results

www.briggsandstratton.com

slomo

 

[stoshzack]

Never heard of "iron coated aluminum bore". I suspect it is aluminum bore, most 25 series were, and you used the wrong rings and aluminum bore is now scored to pieces. Aluminum bore has special coating which hone quickly destroys also.
Walt Conner

Used Oregon rings with compatible part number for Briggs.

quick way to check the bore material is with a magnet, if it pulls it or sticks to it, Cast iron bore, if not, aluminum.
OP, does the engine have the letters "I/C" on it anywhere?

yes, see above pic

I actually got it up and running yesterday. Will test it later in the week.

Thanks everybody for the replies

 

[Scrubcadet10]

Cast iron bore, so it can be honed. Technically it's hole bored out of aluminum, with a iron sleeve pressed in.