I would try to decarbon the head, top of the piston, and around the valves real good, inspect the bore, and bore to piston clearances ( this should tell you if you have excess wear in the bore), clean up the head gasket and retorgue the head or heads and check compression again see if it come up.

Clean with the piston to the top so you don't get the bore dirty and wash out with carb. cleaner before you let the piston rotate down. Wipe the bore out and bring the piston back up. Same with the valve wash out with carb. cleaner and check the valve seats, and valve to seat fit.

You did not mention the engine model. After years of service, the engine may have experience some erosion on the valve face. This results in reduced valve clearance and reduced compression. Generally, it is cost effective to service engine valves adjust valve clearance.

Rebuilding a complete engine is not normally cost effective - unless this is something you want to do.

Does this engine have a ACR ? If so,do a "leak down"test. JMHO

B&S 12 HP electric start ...model # 281707 type 0137-01 code #88052011

Unless you ran the thing low on oil and it got hot probably don't have that much wear. Probably just carboned up, head bolts have loosen, Valves carboned up and not seating. take the head off, what have you got to loose except maybe a finger nail.

Maybe it's the compression tester?

It's possible. I've seen readings of 55lbs to 155lbs posted lately. ;^)

Any luck?

Ted

I would never start any kind of 4 stroke gas engine without first checking the oil level.... infact mine is overfilled....the oil is too clean to get an exact reading....better to too much than too less I know it says not to overfill past the full mark....and when I first start it lots of blue smoke comes out the exhaust..I know the oil is probley gettin' into the carb from the side valve cover....someone mentioned the compression tester may be off on its reading....right now up in this north country its gettin' too cold to be workin' outside on this ridin' mower...I have attached a 42" snowblade to it including new tires and chains...I really want to try it out this winter see how it does with the snow blade....cause it does a good job cuttin' the grass....just like to make it an all season machine...I also keep it outside no room in the shed for it...anyway I really appreciate all the help as this rider is goin' on 20 years old bein' an MTD built mower ....I guess it don't owe me anything even if it blows up tomorrow...I'll just be out the $270.00 I paid for it....Thanks very much for all the input....Ampa

The same company that makes PB Blaster also makes a product for cleaning up the combustion chamber and valves for small engines (I believe its called Lawn Mower Tuneup or something like that) Anyway, its supposed to boost compression in tired engines (whether temporary or long term i have no idea). I have had pretty good results with it using it my 20hp Kohler and a couple small Briggs engines. The stuff seemed to really do a good job of cleaning the exhaust valves and combustion chamber (from what i could see thru the spark plug hole). I can see how compression would be boosted if its cleaning the valves and sealing up the chamber. Worth 5$ for the can? I think so, might be worth a try for your 12hp Briggs.

A cold compression test will yield a lower reading because nothing has expanded from heat. All compression tests should be done with the throttle plate of carb held wide open. A minimum of 4 compression strokes or impulses should be counted (watch the gauge face and/or feel the impulse. 2 types of compression tests need to be done. The first test should be done "dry", just position the tester to the spark plug hole (or screw it in if you have a good tester) and crank the engine over for 4 compression strokes. Record your results on paper. Second test (wet test), add about 2 teaspoons of clean motor oil into the spark plug hole. Rotate the engine by hand a couple of revolutions to distribute the oil around the piston and cylinder. Reattach the compression tester and crank the engine over for 4 more compression strokes. Record this reading above the dry test reading. If the pressure increases by at least 5 PSI higher than the dry test reading, it indicates the rings are worn and are contributing to the compression loss (because the oil helps to seal the rings so they can "inflate" like they are intended to). If the pressure does not increase at all, the loss of compression is due to something other than worn piston rings. Cylinder leakage tests using compressed air are now considered the best method of determining who the culprit is causing the incontinence.

Decarbonization of combustion chambers on inefficent old engines is routine maintenance. That is if you expect them to last for 10 to 30 years providing you done the minimum routine pre-ventive maintenance. Small gas engine that are flooded regularly, seldom started, air filters rarely cleaned and oil not checked or changed (Ampa this is a general statement not directed at you) aggrevates the problem and causes most small engines an early death.

I got a 37 year old tiller thats had the head and carb.off atleast 8 times. I have never changed a gasket on it. It probably has less than 150 hours on it but if I didn't routinely do a system clean up it would of been trash 25 years ago. Only thing I replaced on this is the starter rope and last year a set of points and condenser cause it would not fire after setting out for 2 years.

Ampa

If yours is like mine then the dipstick tube is held to the blower housing with a sheetmetal screw. If you remove the screw you can lift the tube out of the sump area where the drain plug is. Any gross overfill will then flow out of the old style oil fill on the case right above the drain plug.

Am I making sense? When you remove the tube you will find the (3/8"?) NPT threads for the old style standard fill cap. Let me know if you don't get it and I'll try to post a picture of mine.

Ted

I've seen none unless I go back through the old archives.....thanks Ted for the info...it may take me awhile to find the dicussion on this issue but I have lots of time to spare now days

Actually the buildup of carbon would give you a higher compression ratio, but the buildup of carbon on valve
faces and seats would cause leakage. Compression readings
are seldom of any value on lawn mower engines.
Doing a complete proper valve job on an engine with a lot
of wear will boost the compression, but it will also
boost oil consumption. If it starts and runs with some
smoke, I would run it and keep an eye on the oil level.

Fish

I purchased this rider used ....and also it was night time...anyhow I needed a rider so bad ...I'm gettin' up in age now and I can't do things I done 20 years ago....and I didn't want to miss out on this as I missed out on a three year old Murry for another $30 more a month before I bought this one..I'm still kicking myself in the rear for bein' so slow....anyhow I've spent a lot of money on this rider so I may as well continue to do so....anyhow guys I really appreciate the input maybe all your suggestions will save me in thelong run...I know these ol' B&S are hard to kill and this seems repairable....good idea of the screw in compression tester as I do have one of those as well......and a dry test is what I done but not too sure I had the throttle wide open....I did read one time shooting oil through the plug opening and valves were leaking around the valve seats...of course I'm talking a car/truck engine....getting all these good suggestions makes me feel a lot better...if I can get through the winter with it I'll be happy once again thanks ever so much for the great input take care ...Ampa

Hi xpostech...I noticed you read my post on over filling my B&S 12HP engine....your answer on getting the extra oil is what I needed to know of all the push mowers I've owned in the past they had the old plug type so it was not too easy to over fill these engines...I guess I'm just not to familar with the long plastic dip stick tube...I'd just be afraid of messin' up the oil ring..unless these come out real easy....as it's been so far with me workin' on this machine.....I've broke quite a few bolts and what have you...I'm lucky I bought the old Canadian Tire Mastercraft for the parts....anyhow I didn't get to keep the old engine off this parts rider as the guy only bought it for the old frozen up engine nothing else....I just happed to need the transaxle and the mowin' deck so he gave me the whole unit....anyhow I needed to find out how to get the extra oil out....your suggestion is the best...Thanks ever so much and take care...Ampa

But compression readings are really useless on lawn mowers.
If it starts and runs, then leave it alone.

One other suggestion to remove excess oil in engines and trannies: I went to my local pet shop and purchased a hypodermic syringe and some air hose for an aquarium that would fit on the tip of the syringe. I cut the air hose for the length I needed to suction out excess oil in hard to get at places. Just stick the hose on the syringe, and stick the other end in the hole for refilling, etc. Pull the plunger up and watch the syringe fill with oil, etc. It works real well. I've also done the same thing with a flavor injector syringe, but make sure momma doesn't know about it. It has a tendency to leave a strange taste in the food. :)

I removed the long plastic tube with the dip stick attached a couple of days ago...as instructed....I put a oil drain container under it to catch the oil....to my surprise...not too much really came out....so maybe it's not as over filled as I thought...and then I put the oil tube back....and started it up.....and this time it did'nt smoke at all...but today when Istarted althoughit started fairly easy...plumes of blue smoke came out...and taperd off as it warmed up as it normaly does...I know for one thing the top of the piston is gettin' lubercated....I was reading a post about B&S engines where a fella drained all the oil out and run it full throttle for about 20 minutes and nothin' blew....he said that this engine was knockin' and he had no use for it...just wanted to see how long it would take to throw the rod....he let it run full trottle and the only reason it stopped was t run out of gas...he then filled back up with fresh oil...and used it for...another few years...and finally gave it to a neighbour who still uses it to this day....I don't know kind of hard to believe don't you think ?..makes me think maybe I should take the advice of the post from Bill Kapaun and just run it till it dies.... if it ever does...It probley will just run out of gas it does guzzle it down pretty good.....thanks guys take care Ampa

yea bill is usually right.........................

To draw excess oil out of crankcase,a turkey baster is much more efficient/faster.Find them at yard sales for$.25 more,or less.tbk