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My Push Mower:
Yard Machine; 4HP 22"

Engine:
Briggs & Straton
Model: 10A902
Type: 2171B1
Code: 00032955

Air gap: .010
Plug gap: .030"


Last time I ran it - this year - it was hard to start, but seemed to run okay and finished lawn (didn't die, as I recall).

I removed air filter - for testing purposes.
I push primer bulb 3 times (gas squirts) - and engine only pops 3 or 4 times.
I spray starting fluid in carb and the engine only pops 3 or 4 times.
I remove plug and spray fluid directly into plug hole - same result

I have spark.
Dip Stick - shows oil full.
New spark plug.
New / rebuilt magneto
Cleaned fuel tank assembly.
Cleaned carburetor.
Replaced carburetor gasket and diaphragm.

So, I removed head - see photos:



It will be easier to see the difference if you open each image in it's own window and view side-by-side.



- only one of the valves opens and closes when I pull on the start cord. Is this my problem?

Yep, that's a problem.

Can you tell if carbon is holding the intake valve open? You might be able to clean it out but from the looks of things, it may be time for a rebuild or a new engine. Or new mower. Looks like it burns a lot of oil.

Thanks Cpurvis.

So, maybe that's why it "pops"? no compression because that upper valve is staying open?

I've never taken an engine apart before, but I've got the head off - so I guess I'll just keep tearing into it (not sure what I'm doing, but it's either that or junk it).

As far as burning oil, not really sure; I think the plug does get a bit fouled. It smokes small amount at start up sometimes, but not after running for a minute or so.

cpurvis said:

Yep, that's a problem.

Can you tell if carbon is holding the intake valve open? You might be able to clean it out but from the looks of things, it may be time for a rebuild or a new engine. Or new mower. Looks like it burns a lot of oil.

Click to expand...

That's a lot of carbon on the piston and valves. I would imagine the valve guide or rings (or both) are shot.

You're right in that you have nothing to lose by digging deeper at this point. Have you ever overhauled a small engine? You could use a few specialty tools, such as ring compressor and valve spring compressor but some people can get the job done without them.

As a plan 'B', you might check out the Briggs website and look on their 'repower' section to see if there is a bolt-up replacement for you engine.

Lots of small engine sellers online, too...Tulsa Engine Warehouse, Jack's Small Engine, Surplus Center are a few.

Thanks Cpurvis,

No real experience rebuilding engines, but I have some automotive repair background and I'm just going to "go for it" (otherwise I have a tendency to get bogged down in studying a problem and thinking about - - and so less likely to even try).

Thanks for the good info.

cpurvis said:

That's a lot of carbon on the piston and valves. I would imagine the valve guide or rings (or both) are shot.

You're right in that you have nothing to lose by digging deeper at this point. Have you ever overhauled a small engine? You could use a few specialty tools, such as ring compressor and valve spring compressor but some people can get the job done without them.

As a plan 'B', you might check out the Briggs website and look on their 'repower' section to see if there is a bolt-up replacement for you engine.

Lots of small engine sellers online, too...Tulsa Engine Warehouse, Jack's Small Engine, Surplus Center are a few.

Click to expand...

Okay, finally got a chance to get back at it.

I began dismantling, but ran into a problem sliding this base-plate off the drive shaft (sorry, don't know the nomenclature) - see photo.




I watched a video and the guy dismantled and slid that plate off the shaft with very little difficulty.

I don't see a key in any keyway - so I'm guessing the seal (bushing?) is just really tight? I will wire-brush shaft down to shinny metal and spray with penetrating oil - let is sit in the sun for a half hour or so and then see if I can connect one of my pullers.

Any other suggestions on gaining access to the guts of this engine? how to slide this plate off the shaft?

thanks

WilburKlick said:

My Push Mower:
Yard Machine; 4HP 22"

Engine:
Briggs & Straton
Model: 10A902
Type: 2171B1
Code: 00032955

Air gap: .010
Plug gap: .030"


Last time I ran it - this year - it was hard to start, but seemed to run okay and finished lawn (didn't die, as I recall).

I removed air filter - for testing purposes.
I push primer bulb 3 times (gas squirts) - and engine only pops 3 or 4 times.
I spray starting fluid in carb and the engine only pops 3 or 4 times.
I remove plug and spray fluid directly into plug hole - same result

I have spark.
Dip Stick - shows oil full.
New spark plug.
New / rebuilt magneto
Cleaned fuel tank assembly.
Cleaned carburetor.
Replaced carburetor gasket and diaphragm.

So, I removed head - see photos:

View attachment 32365

It will be easier to see the difference if you open each image in it's own window and view side-by-side.

View attachment 32364

- only one of the valves opens and closes when I pull on the start cord. Is this my problem?

Click to expand...

Once you get all that rusty crap off the crankshaft, the crankcase should slide off without too much trouble.

Keep in mind, other parts may come off with it, such as cam and oil pump. Take a peek inside now and see if it looks like other stuff is coming off with the crankcase.

edit: Don't use a puller on this unless you absolutely have to. You'll be risking damaging the crankshaft "bearing", which is nothing more than a bored hole in an aluminum housing, if you do.

I pulled it off.

First, I cleaned up the shaft with a wire-brush wheel, but I couldn't get to the rust on the shaft inside the bearing/bushing/seal, so I heeded your caution and used minimal force with my puller. Instead of using a wrench, I just used my hand to turn the nut on the puller - a little bit at a time, spraying penetrating oil a couple times more and it finally slid free; cleaned the rust off that section as well.

2 Questions topics:


Carbon
At some point, I'm going to remove the valves and piston to clean off that black gunk. So, what's the best way to clean this "carbon", etc? Soak in kerosene; kerosene mixture? wire brush? steel wool?


Rings
I guess I'm going to try and remove the rings too to get in there and get things clean. I don't have specific tools, but I'll improvise.
Should I be able to remove the rings without breaking them? and then put the used rings back in place?

thanks

ps Anybody can jump in here on this conversation. Just to clarify, I'm not trying to do this job "perfectly". I can be a sort of a perfectionist, but that sometimes gets in the way of my even getting started. So, I'm just diving in; learning as I go ("shade-tree mechanic"). I bought this old machine, second-hand about 8 years ago and it would be cool if I get it running, but not the end of the world - if I scrap it and buy a replacement engine to bolt on in it's place.

cpurvis said:

Once you get all that rusty crap off the crankshaft, the crankcase should slide off without too much trouble.

Keep in mind, other parts may come off with it, such as cam and oil pump. Take a peek inside now and see if it looks like other stuff is coming off with the crankcase.

edit: Don't use a puller on this unless you absolutely have to. You'll be risking damaging the crankshaft "bearing", which is nothing more than a bored hole in an aluminum housing, if you do.

Click to expand...

Carbon: I don't know of an easy way to remove it. I suppose some kind of bead blaster would work well but I've never had access to one, so don't really know. I don't know of any chemical means to remove it, either. The only way I've removed it is scraping and brushing, being careful not to scratch the head gasket sealing surface. Hopefully someone else will chime in with a better way.

Rings: Yes, they can be removed without breaking but I wouldn't reuse them.

Problem Solved - Re: B&S - Won't Start, Valve?

Thanks Cpurvis,

I held off posting until I ran the mower a few times to make sure I was good to go (and then procrastinated posting again).

And I seem to be okay.

So, what I did: I cleaned up that bottom plate and managed to slide it off to gain access to the guts.
I removed the valves and found that the valves were "stuck" because the shafts were kind of caked with a sort of hardened oily clay looking material. I'm pretty sure this was dirt that got by the filter over the many years of mowing in a dry dirty environment (I tend to kick up a lot of dust) even though I use a filter and clean it.

I'm no expert - obviously - but the machined surfaces look surprisingly clean, smooth and un-scarred. I didn't buy new rings; just cleaned and reused (minor pain getting them back on).

I was really frustrated trying to get the valve springs back in and then eventually I remembered a youtube video where a guy used a vice. First - be sure to wear eye protection - I compressed springs in a vice - all the way and then used two cable ties on each spring to keep them compressed. That kept them compressed while I re-installed the valves.

This old machine now runs very well - seems to burn pretty clean. I'm glad I took on this challenge - confirmed what I suspected all along - that I really could take my small engine apart and make most repairs on my own. I saved myself some money too.

Thanks Cpurvis and thanks LawnWorld

Congrats !

On an inexpensive push mower , I always try to compare the cost of repair to the cost of a new mower , on sale .

I worked maintenance years ago , at a local hospital . The grounds department would get several , purchased on sale , push mowers at the start of the spring . About 1/2 way through the mowing season , they would receive some more purchased on sale push mowers .

They said it was cheaper in the long run , than doing / paying people , to do major repairs .

Now , when I work on my mowers , I always think , how much are the parts going to cost me , on a used / several years old mower ? Not figuring in my time .

The more expensive the mower is , may change the cost analysis .

Best wishes ,
Wyr
God bless

You're very welcome, WilburKlick! Glad to be of assistance.

When you removed the rings from the piston, did you pay attention to which ring came out of which groove and which way they were facing? The oil ring is not a problem, but many times compression rings have a bevel or a step on the ID of the ring. New rings come with an instruction sheet telling which way they go.