Heymow - Lawnmower Racing Forum

Engine Help => Briggs Flathead => Topic started by: Mick on August 06, 2021, 09:05:21 am

Title: rod knock/piston slap or valve lash clatter????
Post by: Mick on August 06, 2021, 09:05:21 am
Why why why does my opposed 18 hp make so much motor noise... when running. it is pretty quiet when it is not running. is piston slap LOUD? apparently putting stock pistons into motor that has at LEAST .016" distance/feeler gauge tween piston skirt and cyl is a tad excessive? and the .010" piston rings  i file fit to the stock pistons that gets me 60 PSI cranking pressure (too much?) might not have been the very very best thing to do. i did hone it out and dremeled the BIG lip out of top of cyl so i cld get pistons out without beating them /the rod to death.

am running 20-50 oil with 20% STP OIL TREATMENT so the oil is thick thick thick when cool 80* and it is sort of quiet(er) when cold but that doesnt last long when the motor is warmed up in 5 mins or so and temp gets to 200* with temp gun on cylinders/heads.  got 20 hours on test stand so far, starts pretty quickly, runs ok when warm, does have intermittent miss . think i can get 100 hours out of it? more as long as i dont scream it to 4500R's too much? it did it, didnt blow up/throw rod/flwheel explode. donthave kevlar scatter shield around the flywheel like i wud like to have anything over 3500R's. going to be down a little on HP since the air is thinner here.... 13% less power. 3% for each 1000' of elevation and 1% for each 10* over 60*... x 60 PSI cranking pressure so... 18 HP is now... 15 HP? a little less? EPA prolly isnt too happy with it.

im sure it will be fine, dont u think?