Export thread

My vintage B&S Flathead push mower is getting low on compression. Since it does not burn oil & plug is clean, I suspect the valves, in particular the Exhaust.

There is no valve lash adjustment in the conventional sense on this Flathead. Mow season is possibly close to over, So when done, I'll remove the head, rotate crank to .250" past TDC & see if the valves are closed tightly.

Likely not, so I'll have to remove each valve (only 2) & grind / file a few thou off the valve head (tip) & recheck, till I get .005 -.007 for Intake, & .007-.009 for Exhaust. Then close her back up. Flattys use a metal composite head gasket, so it is re-usable in most cases.. The side door to the valve springs & tips gasket will need replaced, & I'll just make a new one.

So I wanna find some torque specs.

I've had pretty good luck with lapping compound, as long a seats are solid in block try removing springs and lap them in, i have a suction cup tool i had for aircraft engines that works very well after cleaning top of valve.

The gaskets are not reusable
Usually only the exhaust will need attention
You lap the seat then shorten the stem to compensate for the valve being further down the block
Very common to find the valve not closing at all
Inlets very rarely need any attention.
The B & S book has lash measurements for both spring in & spring out but I have never had any luck using the spring out measurements.
Set them right up to the maximum because they will get tighter with use as the seat wears.

Thanks Guys- Yes I am equipped & experienced w/ lapping valves. I did plan to lap the Exhaust at least.
Which is the ones I suspected for the low compression.. Funny mower still runs smooth. Just not near as powerful.

It sure looks to be a tiny place to get to valve springs.. But I"ll have to use my forceps or similar..

Yes I'll set them to max lash, (Thanks Bert),..

Here.

Thanks Fish, I found mine, which is an "L" Aluminum Head Flatty, & Model Series 10T502, Thanks for the link, That I've saved (of course) it will get me real close..
Have my valve lash specs in the original owners manual.

This works excellent for flathead valve springs, https://www.amazon.com/gp/product/B001OK9TRK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
a little pricey, i think, but it saves my knuckles using a flathead screwdriver to pop the keepers in place

Scrub- Thank You, that does look like it is worth alleviating a lot of aggravation.

Not gonna tear this mower down till end of mow season. it still runs smooth.. Just not as strong as it should be,..

How about a source for a COPPER head gasket for my "L" head Briggs ?

Like I have in my Favorite Flatty..

contact Lanni at copper gaskets unlimited from memory he has patterns for all of the common mower engines .
I think he does your gasket as a stock item or will cut one at any thickness of standard USA copper sheet gauges
The Intek gaskets put an end to repeatidly replacing those gaskets forever .

Thanks Bert, I will get with them. That will save me from shaving the head a bit anyhow.

I have copper ones in my 45 Harley Flatty, that I Bored & Stroked to 59"....... Plus about every other mod I could think of.,.

Lanni is a really great person to deal with .
I send him over scans of obsecure gaskets and in a month a perfectly cut set arrives in the post.
Nothing has ever phased him.
HE will go to the effort of working out the maximum number of gaskets he can send without jumping up to the next post price bracket .

I think that is the place to get what I want.. Mine may not be so obsolete, but want copper about 1/2 the thickness of the oe ones..

Thanks again for the link to him..

OK, getting more serious about this Engine, I was assuming it was just valves. Which shows what assuming gets me...

But did cold Compression Test today... Air cleaner off & throttle WFO.

Cold & Dry: 50 psi

Cold & Wet: 80 psi

By wet I mean I added a spoonful of oil in spark plug hole & re-tested.

Quite a Big difference. Rings seem to be getting weak as well.. I know I should have done my testing before I even started this thread. My bad..

Appreciate any & all input..

Hope you don't see this on teardown. I found out the hard way that today's oil is not so good for old aluminum bore Briggs engines. Look close and see that the top where the rings still run is ok. Down lower the bore is not only scored but metal is actually being pulled off from the piston contact. Motor was running decent but using some oil.

Yeoww, !!! Thanks for reply & that is shocking ! ! ! Never thought it "might" be aluminum bore. Mine uses "0" oil, but has lost power.

I've only run Castrol HD 30 in it. I'm not sure it is worth total rebuild. It was only a $149. mower when I bought it new in early 2006

It is model: 10T502 0457 E1 & Code: 06053152

PartsTree shows .020 rings available but not the piston, Std rings and piston are available $108 for a std ringset and piston.

I'd say you got your money's worth on that mower. If really damaged you might do a Surplus Center or Harbor Freight motor swap and get another 14 years?

Tom- Why do you suspect oil did your damage shown ? I am extremely curious.

Wife hit a rock about 5 yrs ago on mine, crank got slightly bent, I got it straight as I could. I didn't think it would last this long after that.

I wouldn't mind re-powering it tho.. Or getting something w / Honda power.

Scrub- Appreciate the parts & prices, it is not worth a full rebuild.

Shortblock is available for $158 PN 398210 of course then you have to swap stuff over...
Might look at smallenginewharehouse.com, they have filters so you can search for specific crank lengths, diameter, HP, etc. and they'll show a compatible engine.

Scrub- Thanks man. & after all that, I still will have an old deck with bad wheels (again).. I re-bush them. But that only lasts so long.

I wouldn't mind some new pusher. Probably Honda powered.

7394 said:

Tom- Why do you suspect oil did your damage shown ? I am extremely curious.

Click to expand...

That topic has been beat to death these days. Barrier lubrication, eliminated from most current oils, extremely important with flat tappet cams and here with the untreated unsleeved aluminum bore motors.

Yep, I'm on board with Good oil for my Flat tappet Kawasaki.

But musta missed info on the un-treated unsleeved aluminum bore engines..

Thanks..