OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines 19.5 briggs

Have a 19.5 briggs single piston on zero turn. Starter got to where it would not spin motor. Changed battery, and starter (twice). Still locks up on compression stroke.

I was told these new briggs has a decompression lobe on the cam. But I bought a manual and it does not say anything about that. I took the valve cover and drilled a small hole over the exhaust valve. I can stick a small screw driver and hold the valve down just a little. I have to hold it open till the engine starts trying to fir when I release the valve the engine will start and run fine till I kill it then have to depress the valve to start it.

Doe anyone know if there is a decompression valve on it and where it is located.

Thanks.

Hi Alton, welcome to Outdoorking.

The only 19.5 hp single cylinder Briggs I know of, is an Intek. If you post the Model, Type and Code numbers which will be on the engine top cover or cowl, we can identify it specifically and make use of the Briggs tech manual.

The Intek does have a compression release, and it is likely to be the cause of your problem. The starter motor does not have enough torque output to crank your engine through the compression stroke unless the decompressor is working. However the decompressor works by bumping the exhaust valve open momentarily in the middle of the compression stroke at cranking speed. Above cranking speed, it disengages and the engine has full compression. Unfortunately this means that the adjustment of the valve clearance is very critical: a slightly loose exhaust tappet will prevent it from working, and the result will be a burned out starter motor. This is why the Briggs operator's manual says you must adjust the valve clearance once every year: a small amount of wear in, for example, the rocker pivot, increases the clearance and leaves the decompressor not working. Furthermore after a substantial amount of use of the engine, the decompressor's operating mechanism on the camshaft wears down, and the valve clearance adjustment becomes more and more critical, until it stops working altogether, even at minimum specified valve clearance. When that happens, it is necessary to replace the camshaft since the decompressor cannot be replaced separately.

So, please do these things:
1. Post the Model, Type and Code numbers so we can make use of the tech manual in this matter.
2. Measure the valve clearances for both valves, and post them. If you are not clear on the procedure for this, I will explain it. Note that not all Inteks have the same specified valve clearances, so we need the Model, Type and Code to explain it.
3. If the clearances are not within specification, adjust them carefully to correct this. Once again, I'm happy to explain the process.
4. If the engine will still not crank over the compression stroke when the clearances are correct, we can further discuss the implications.

This is all I can find on the engine

BRIGGS & STRATTON PPROFESSIONAL SERIES 500cc 19.5 hp

then on a white strip on front of engine

engine family ABSXS.5002VP 279222
EU e11*97/68SA*2004/26*0333*03
Displacement: 500cc ECS: EM
EPA Compliance Period CAT: C
DOM: February 1010

I had adjusted the valves according to the manual, but the manual did not list any professional series. Should not have made a difference. There are not many hours on the engine.

Hope this helps

Thanks
Alton

Alton, please take a look at this video:
http://www.jackssmallengines.com/jacks-parts-lookup/briggs-stratton-model-locator.aspx

I think the Model is probably 31P677, and your mower might be a John Deere, but we need the Type as well as the Model to find the parts list, so please run through that video and see if you can supply all three numbers. (The Code tells us the date of manufacture of the engine.)

I'm not really clear on how many hours it takes to wear out the camshaft so it needs replacement - it is hundreds of hours, not thousands though, this is not a car engine. What is probably more relevant here, is that the slight wear on the moving parts that increases the valve clearance and causes a problem, can happen right from the start, as the parts bed themselves in.

Sorry the motor in on a husqvarna zero turn

model type code
E1Q677 124B1 100210zd

these were on the tappet cover.

hope this helps.

Thanks again
Alton

There are anomalies in those numbers, Alton. The first two digits of the Model number are normally the engine's displacement in cubic inches, which I think is 31 for yours, not E1. More importantly, the Type needs an extra digit. There are four numbers for the type, then usually a hyphen, and two numbers or letters for the trim. The hyphen may be omitted, but there should be six numbers or letters altogether for the Type/Trim, so there is one missing in what you posted.

Incidentally the Code tells us your engine was made on 10 February 2010, so as you said, it isn't all that old.

you were right took the tappet cover so I could see it better.

model
31Q677

TYPE
0124 B1

CODE
100210ZD

maybe these numbers will give you more info, sorry I got them wrong.

Thanks

Alton

Thanks Alton, now we are getting there. Here is your Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/iorvDKJU0HCjhJvcv4.pdf

Here is your Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/18kvuCXNnfBhU7y.pdf

I suggest you download this manual - it is free, and is the official Briggs overhaul manual for all the single cylinder Intek engines:
http://www.ccdist.com/_serviceManuals/briggs/276781.pdf

Your engine is referred to as the 310000 throughout: you can find all the specific references to your engine just by searching for that number in Acrobat. Here is an illustration of your compression release, from page 140 of 179, in the manual:



You can see that there is a piece of stamped sheet metal attached to the camshaft, and pivoted so that when the engine is rotating very slowly (cranking), the stamped piece is edge-on beside the cam, and projects so that it stands up slightly higher than the cam. As the cam rotates, the edge of the piece of metal strikes the cam follower and lifts it up until the stamped piece has rotated far enough to be past the cam follower. This is the decompressor action: the exhaust valve is bumped open momentarily about halfway through the compression stroke, so the compression process has to start again for the second half of the stroke, and only a relatively low pressure is developed in the cylinder: about 80 psi. When the engine starts running, a centrifugal weight moves and allows the piece of stamped metal to pivot out of the way, so the exhaust valve is not bumped open during the compression stroke, and the full compression pressure of about 150 psi develops in the cylinder.

The problem is that the stamped metal does not stick up very far above the camshaft, so if the exhaust valve has slightly more clearance than it should have, the valve will not be bumped open at all, and the starter motor will be trying to crank the engine against a compression pressure of 150 psi. It will fail at that task, and if you keep trying, it will burn out. Note that the edge of a piece of stamped metal is not a very durable object, so after a time, it wears down and the decompressor doesn't work anyway.

So, it is critically important that you set the valve clearances precisely accurately. Now, if you go to page 175 of 179 in the manual, you will see that for the 310000 engine series, the required valve clearance is 0.003-0.005" for the intake valve, and 0.005-0.007" for the exhaust valve. Please check the actual clearances you have, very carefully with the engine cold, and report back. You should be aware that the problem you have is a very well known one, and a lot of servicemen set both intake and exhaust clearances to 0.004". I do not recommend that, since it is below the minimum specified clearance for the exhaust valve, and could in theory result in a burned valve. However given the very common problem with decompressors, it is easy to understand why they do what they do.