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wfopete

Help on Poking around a B&S

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wfopete

Recap:

On the first cutting of the year my C-111 died on me yesterday while mowing. It acted like it was running out of fuel, even though it had a full tank and was getting fuel to the carb. The B&S carb looked pretty grungy so I removed it to check it out. Surprisingly the carb was remarkably clean.

The latest:

Ok so I put everything together checked for spark and it was good. Then I put my thumb over the spark plug hole for a poor man's compression test and got a weak puff. So I put a gage on it; 30 PSI <_<

The motor is a Briggs:

Model: 252417

Type: 0245-01

Code: 81021711

I don't know why it died the way it did, maybe a broken valve spring?

Any suggustions? Is it worth pulling the head for a look or is it time for a Kohler?

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W9JAB

:D

30psi is very low. I would see if I

could adj. the valves, and recheck

the comp.

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wfopete

The thing is it took about 15min for this to happen from starting the engine to having the engine quit and not restart even when cold. Would a valve adjustment issues have these indicators or does it sound like sumpin' done broke?

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W9JAB

:D Well if say, the intake valve hangs

open you would drop compresion, and

would not be able to start the motor.

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wfopete

I'm kinda suspecting something in the valve train, I just find it strange that a valve would "stick" while the motor was running. Never know though, stranger things have happened.

I guess I'll pull the head and have a look.

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KC9KAS

The B&S doesn't have an automatic compression release like a Kohler resulting is a low compression reading, does it?

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rick

Briggs have a compression release feature, but I tend to think maybe a valve isn't sealing, either stuck, as has been mentioned, or maybe carbon on the seat.

Time to squirt some oil in the cylinder and check compression again. If the oil doesn't raise compression much, I wold remove the head and check the valves.

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KB9LOR

I had a Briggs do the very same thing, ran fine, then no power, turns out one of the valve guides was trashed, and there is no way to fix them, once those guides go it is junk.

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linen beige

one of the valve guides was trashed, and there is no way to fix them, once those guides go it is junk.

:D

Time to find a mechanic instead of an engine salesman.

Pages 141 and 142 of this http://www.scribd.com/doc/9379684/How-To-R...tratton-Engines manual walks you through it. Note they list Briggs and Stratton tools for this operation.

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wfopete

Well a little bit of SAE 30wt got me to 50 psi on the compression gage. So off with it's head and

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rick

Rotate the crankshaft with the head off, be sure the valves are moving up and down.

It's time to remove the breather, and check the valve/tappet clearance. Intake .005" to .007", exhaust .009" to .011".

If that checks out the next step would be to remove the valves and inspect them, and their seats carefully.

Finding nothing obviously amiss, I would lap the valves to be sure they are seating properly.

If the top end checks out, the problem is in the cylinder.....

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wfopete

The valves were moving up/down fine but it will be next week before I can go further on checking adjustment or condition of the valves.

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Horse Fanatic

I have an 18 hp 2 cylinder Briggs which had low compression on one cylinder. The engine ran but poorly (only on one cylinder). All I had to do was lap the valves on that cylinder and adjust them and the compression came up to within 10% of the other cylinder.

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wfopete

Well, I popped the breather cover off to check the valve clearance. The exhaust valve had a retainer and collar while the intake valve simply had a one-piece retainer holding the spring in place. :D

Upon measuring the clearance I found the exhaust valve clearance to be .016; way too much clearance (over twice the recommended spec. of .005

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rick

Pete, the valve set up sounds correct. The excessive gap you describe will not keep you from running, but the zero gap will. If it were mine, I would remove the intake valve and take a little off the stem end on the side of a grinding wheel or a disc sander

checking frequently until you get the correct clearance. Lap the valve and seat, recheck the clearance, put it together and see what happens. Please don't go Chinese!

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wfopete

Excuse my ignorance on this subject but how do you go about correcting for the excessive clearance (.016

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rick

Short and sweet, you buy a new valve....

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TT

Grinding the valve and/or cutting the seat deeper works too. :D

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rick

True, TT, if you have a Neway set or a valve grinder handy.....wish I did sometimes.

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Save Old Iron

I have used leakdown testers with success to locate fairly large leaks in the combustion area.

If you hear air hissing thru the carb - a leaky intake valve

If you hear air hissing thru the exhaust - leaky exhaust valve

If you hear air hissing thru the oil filler tube - leaky rings / cylinder area

If you hear air hissing around the head / cylinder area - leaky head gasket

Its a quick check but surprising accurate on a Briggs w/o the compression release. Just did one the other day on generator with a Briggs and found a leaky head gasket.

The 1/16th side play on the valves is evidence enough for an R & R of that area.

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linen beige

I would remove the intake valve and take a little off the stem end on the side of a grinding wheel or a disc sander

checking frequently until you get the correct clearance.

If you do go this route try your best to keep the cut end as close as possible to absolutely square to the stem and perfectly flat. It wouldn't be a bad idea to make your first cut a little shy of the mark and finish it down to final length with a flat stone, actually polishing the stem end so it doesn't chew up the lifter / cam.

But I do have to agree that with some of the other symptoms you've mentioned it's time for a rebuild.

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rick

I was sure that holding the valve stem square to the stone/sanding disc would be obvious. It is easy to make a simple guide with a piece of wood. While not 100%

exact, it is certainly sufficient to the task.

I assumed from the first we were trying to get the man's engine running again so he could cut grass, not do a complete engine overhaul. Even replacing/installing valve guides does not require a tear down any further than it would to lap the valves, which still must be done after guide

replacement.

It would be beneficial for anyone contemplating small engine repair to

first acquire the engine manufacturer's manual. They are available at reasonable cost

for most, if not all makes. A perusal of the pertinent manual would allow an individual to decide if the repairs needed are within his abilities regarding knowledge, mechanical aptitude and contents of his toolbox.

Some of us actually do this work to make a living, or as an interesting and profitable avocation, and have seen the costly results of "home mechanickin'".

I'm going to shut up now, and just go back to lurking.

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wfopete

I'll get after that pesky intake valve in a day or so and bring the valve clearance back in spec.

This motor went from hero to zero within 15minutes. No knocking, no smoking, no signs of any trouble just a short period (1 minute) when it sounded like it was "running out of fuel" and then zip. The head gasket looked good with no evidance of a leak. So at this point I'm just interested in seeing if a bit of valve work is what the motor needs to bring it back to life or if it just leads to the next no-run problem. I've never had much experiance with these small engines so I'm curious as to what led to the expedited no run condition. :D

I likely will replace the engine unless it recovers signifcantly with a little valve work. If I do replace it, it will probably not be with another Briggs and Stratton unit. More likely I would go with a 12 HP or bigger Kohler or a far eastern unit as I'll bet a Kohler replacements will be a lot more $.

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wfopete

Ok, I lapped and adjusted the valves, threw on the old head gasket snugged the head down to 25 ft/lbs (which may be too much, does anyone know the correct torque for the head bolts? I didn't find it in the online manual) and ran a compression test:

Dry: It went from 30 to 105psi.

Wet: It went from 50 to 125psi

For a 6:1 compression motor I'd say that's good enough to go buy a fresh head and breather gaskets, put her together and see if she'll start doing some internal combustin'

Hell, I might even pop for a new sparkplug for the old girl.

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rick

Hell, Pete, it'll run now! Best to get the new gaskets, though. Head bolt torque is 165 inch pounds, I do in three stages; 50, 100, and then 165 inch pounds. There is a recommended sequence, but I am not good enough with a computer to put it up here.

It's in the manual, though.

You can cut your grass again!

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