High Performance Mods for my 1.75hp flathead Briggs

#21
what is the taper of the cylinder? i would measure it at two spots 90 degrees apart top, midway, and, bottom. nice job! use a soluble coolant on your final cuts.
 
#22
what is the taper of the cylinder? i would measure it at two spots 90 degrees apart top, midway, and, bottom. nice job! use a soluble coolant on your final cuts.
Well, at most, I'd say my current taper is a narrowing toward the bottom, by about 0.0005".

The standard bore was 2.3125" (ie: 2 5/16"). And right now the top and middle are about 2.3215" -- while the bottom is still around 2.3210.

I may be fussing too much about a totally uniform +0.010" -- top to bottom. I do realize 5/16 is .3125", but aiming for an exact oversizing means chasing a half thousandth of an inch (ie: to 2.3225").

So I'll probably bury the difference and just go large on that last half thousandth -- to 2.323". I'm afraid to go narrow for fear the new piston wouldn't have enough clearance.

Thanks for the coolant tip. You mean like honing oil? I had mixed my own cutting oil last night after running out of WD-40. (3-in-1 oil and mineral spirits).
 
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#23
you don't want a taper but its good to make sure you dont have one that is significant. yours sounds fine. if your hone job is within a few thousandths you will be fine. a person much wiser than myself once said "people should need to get a license to get a micrometer or caliper that measures tenths!"

:D
 
#24
you don't want a taper but its good to make sure you dont have one that is significant. yours sounds fine. if your hone job is within a few thousandths you will be fine. a person much wiser than myself once said "people should need to get a license to get a micrometer or caliper that measures tenths!"

:D
That's my thinking too -- to not overthink it. My Briggs repair manual was explicit that you should oversize to exactly the next size up, and then to go an extra half thousand ("to allow for cooling"). I figure I'm doing just about that -- taking 312 thousands of an inch and making it bigger, to around 322 or 323 thousandths.
 
#25
The cylinder is perfect.

I still had to take off a thou from the bottom, and half a thou from mid and top, and this "Glaze Breaker" hone just made easy work of it.

I oiled up and weighted down the block under the spindle just like the day before... Spun up the drill press to give those heavier spots a little extra attention and feathering... Stopped twice to measure, and I was done.

Now I'm dialed in at half a thou over plus ten just about everywhere, and I couldn't be happier.

I saved the hand drilling for the ball hone and just about 5 to 7 strokes gave me such great hash marks I think even the block enjoyed it :cool: See pics...
 

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#26
After days of honing with stones and ball hone and batches of homemade honing oil, a good washing is important this time and I want to make sure not to leave any grit behind -- like stuck within the fresh crosshatching. Next time I'll try a soluble cutting fluid to reduce the chance of this.

Thanks Phil1958 for the soluble advice ;)

PXL_20220922_194716859~2.jpg
 

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#31
I'm measuring for clearance between the valves and the head, before shaving or even leveling any head or deck material...

Valve lift requirements

Valve face above deck:
1.05mm

Cam lobes, open minus closed:
23mm - 19mm = 4mm

Thus, total valve rise:
4mm + 1.05mm = 5.05mm*
*(Disregarding valve lash)

Head ceiling height

Head ceiling above gasket face:
5.7mm

Copper head gasket**:
1.15mm

Thus, total head ceiling height:
5.7mm + 1.15mm = 6.85mm

Therefore, head/gasket height from deck is 6.85mm, minus valve rise of 5.05mm = 1.8mm clearance

**Note the OEM gasket measures 1.75mm. This means installing the copper head gasket (which is thinner, at only 1.15mm) is equivalent to having already shaved 0.6mm (or, 0.0394") from the stock head.

And because 40 thousandths ain't no chump change, I'll figure out compression next.

Once I have the piston installed...
 

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