(UPDATE) My Vintage Briggs Flathead is getting low on Compression.

[7394]

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.

 

[gainestruk]

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.

 

[bertsmobile1]

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.

 

[7394]

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),..

 

[Fish]

Here.

Briggs and Stratton Valve Clearances

outdoorpowerinfo.com

 

[7394]

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.

 

[Scrubcadet10]

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

 

[7394]

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,..

 

[7394]

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

Like I have in my Favorite Flatty..

 

[bertsmobile1]

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 .