checked my compression and got 60# on each side. don't know what it should be, but damn that seems low to me.

gonna adjust the valves tomorrow, i figure sumthin got to be out of wack.

it been a couple hundred hrs since they put the new engine on it.

motor been losing power and running lower rpm's, especially when loaded.

Got my compression checked this week and the invoice says 180. Don't know what it should be.

I've always heard 160~180.... but I'm on my 4th big block Briggs and I ain't never seen dat kinda compression on any of 'em. I usually see something in da 120 range. 60# is definitely low.

I think its like 120 stock after heads was mod it was 180 but 60 is low!!

That sounds low to me too. The valves on the big block briggs start to leak after a while, I'm guessing thats your problem...

WHat is the best way to keep the valves seated? I remember back in high school there was and abrasive liquid (with the consistancy of gojo hand cleaner) and he would lightly chuck the valve from a 3.5 HP briggs in a drill and run it on the head to get a better sealing surface. I know it was not PROPER and 100% true but it seemed to help the little motors hold compression.

wen I took my eads off, nieter of te intake valves were seated... in fact, you could see daylit from one side to te oter. before I put tem back on, I used some lappin compound and lapped tem in. I dont know wat all tese uys do wen tey do ead work, but I suspect makin te damned valves seat properly is an important part tat most folks dont know about.

i set the intake and exhaust valves at .006" this am.

they were way out. comp is now 90 and 90.

went g0 put out 80 jugs this am, motor idle was better, but still only seen 3900rpm's once in the shallows. more like 3700ish in the deep, and i got the in neutral rpm's with govenor wfo.
motor just ain't got no mo power.

maybe cam or pushrods woreout? i dunno but i will find out.


i wish the mm co's would come out with the big kholer, i'd buy one today.

joel usually stock with butterfly wide open 145 cranking pressure. it can be 60 if your throttle is closed. got to get air in for compression. maybe that will help you

Thanks Kook. Im guessing over time the seats don't seat quite so well and causing less compression to be built up and you lose overall efficency of the engine.
DA how many hours are on your engine?

I lost load carrying capability in my engine at 40hrs (didn't loose RPM- just couldn't go fast) and had a head replaced by Briggs- Leaking through the intake. Did the headwork on mine when the other one started the same stuff. The folks doing head work concentrate on the valves. I wonder how much HP is being lost across all these motors because the chronically leaking valves?

Just out of curiosity I will search on Briggs motors and see whats the normal RPM to run at. I wander if running these motors at 4k and plus on modded motors will cause premature failure? Or if it is a freak of nature that some engines arent setup under good quality control and have the valves set too loose or not so good machining on the head for the valves to seat properly? Thats odd IMO but so many people say its a lwan mower motor, techincally it is but a lawn mower is usually run at a constant RPM and doesen't see all the load the engines take from consistent throttling up and down and bogging them down in the slop.

well..... checked compression today, with throttle closed around 65#/65# on the guage.

with throttle WFO it is 145# and 140#.

i then checked my valve clearance i set yesterday. i was checking the feeler guage and REALIZED THE SUMMBIATCH WAS IN MM'S NOT INCHES

SO, CONVERTED .006" inches TO MM, WHICH IS .152SUMTHING MM.

SOOO..... SET VALVE CLEARANCE ON ALL FOR TO .152MM AND WENT GO RUN THE BOAT.

boat was empty and almost out of fuel, it seemed to run about the same on top end, but it had noticably more power when climbing on the boat trailer and getting on step.

to be continued next week........

This is a good thread topic !!!

Maxx ~ I have learnt from this MMT site that the factory heads do/can have some variants to them and not of the highest quality fo the optiam performance. I don't know that much 'bout the subject 'cept you gots to have good heads befo' you can have good performance and thay is alot a mechanic feller can do by just gittin' that preasure readin' !!!!

Thats good to Know DA, I hope you get the issues worked out.
And Brooks your statement makes alot of sense too. Most people reccomene when getting mods to get head work done. If you are getting so much improvement out of the engine from some porting, polishing and decking, it goes to show how Well the heads are