Briggs & Stratton Crank

[creia]

In regards to checking the rod to crank condition/clearance on all of our small engines my son and I have always used a combination of visual, micrometer, and finally - plastiguage as a means to determine. To determine the clearance (and which Plastiguage to use) we subtract the Briggs specs for the crank OD from the Briggs specs for the rod ID.
Michael

[Arkie]

He could use plastigauge 1-3 thousands size to check his crankshaft even using a rod from a equivalent used engine of same make.
We/HE knows he has a trashed rod.
.001 clearance and or out of round is easier to detect using plasti gauge instead of constantly using mic's to check oil clearances when you know what you are doing .

[KE4AVB]

The L-head engines are no longer available from Briggs, adapting an ohv is probably not worthwhile unless you have a donor mower. If you really want the project replace the crank if garbaged.

Then that strange as my Briggs distributor is still selling the 650, 675 and 725 series L-heads. Matter of fact the 126M02-1025-F1 which is the direct replacement for OPs motor is listed at 336.30 but you can find one on a new mower for less, buy it and part out the mower. And I know for sure that Husqvarna was still selling them on the HU675HWT trimmers as of last Fall.

When I worked for a dealer we at times buy new equipment and use it top service warranty repairs and sell new parts at a discount as take-offs.

[KE4AVB]

.001 clearance and or out of round is easier to detect using plasti gauge instead of constantly using mic's to check oil clearances when you know what you are doing .

Or even an old style calipers like you use while turning round stock can when set at correctly as they will catch on the high spots and float on the low spots.

[lefty]

Probably. Some have used straight muriatic acid dabbed on the aluminum transferred spots to remove it. The ol' stainless toothbrush helps things along.Then polish with some crocus cloth.

Do you think it wound work on this Fulltilt? Here's a couple picks. You can see the lines, which are not palpable. I thought I could grab something with my nail originally but I was mistaken.

I know to do the job right is to replace the crank. I'm just wondering if it is at all possible to salvage. I know that the longevity of the equipment may be compromised by doing it but this machine was given to me.

[Arkie]

AND
I've seen couple of rods that were out of round and surprised the crank was still with in specs and no signs of any scoring at the rod throw and re-useable.
Both times it was on outboard motors (Johnson/Evinrude types) and could hear a harmonic knock.

Suspect a needle bearing would start sliding instead of rolling and ruin the rod and the problem was found before the rod ruined the crank or the rod cap broke. (and piston not be scored)

Scored piston on a 2 cycle outboard usually indicates the block overheated and most generally due to a weak or bad water pump. Sometimes you can see the paint charred at the piston jug area as a indicator of overheating and piston has been scrubbing the cylinder wall before tear down.

[lefty]

So aside from the condition of the journal, scoring, transfer and so forth, I should be concerned with and check for out of round?

[bgsengine]

If it is just for you and you are not worried about how long it will last, I would say just polish it lightly with crocus cloth (3/4 inch wide you can get from auto part stores, etc) and just polish it until you get a nice shiny finish and then take a close look at the journal on either side of the rod (a few millimeters) where the rod chamfer will be and see if you can detect a wear ridge and how deep it is - if it is out of round or worn heavily you can usually see it - but if it is not too bad, you can slap a new rod in and run 'er til it throws the rod - assuming again that it is yours and it's gonna be for personal use - It could last for many more years with maintenance, or it could throw your new rod in the first hour. I have done them myself just that way , taking no measurements , and had myself a walk behind mower that I used for 3 more years of life out of it til the deck rusted out.

[lefty]

Thanks BG. Yes, this machine is just for me and I already have a Toro Z-turn so to be honest, I won't be beating on her too badly. And I take very good care of my equipment with regular maintenance.

Just a quick question regarding the crocus cloth. Is it the fine grit we're after or is there something special about it. The reason I ask is that I have an enormous amount of abrasive at my place. I have enough sand paper, scotch pads and other to last a lifetime and more. I have paper from 40 grit up to 2000. I have micromesh up to 12,000 and a slew of cutting compounds. I also have a leather belt I'll often use.

Is there anyway I can make do with what I have in house or is the crocus cloth your hard and fast recommendation?

Thanks

[Arkie]

So aside from the condition of the journal, scoring, transfer and so forth, I should be concerned with and check for out of round?

Try to clean up the crank first removing the aluminum transfer so as to see the condition of the metal throw and then check for out of round, then see if you can find specs. If you can find the Briggs crank rod throw specs and you do not have a micrometer, take the crank to a machine shop and ask for the SERVIVR manager or owner) and have them mic the crank per the spec's you give them. (you need to tell them what the specs are so as they are not wasting valuable time messing around with it and they will be more friendly with you, usually.) They know they are most generally not going to make any money repairing a single cylinder Briggs crank and they are doing you a favor for possible other future work and public relations because they are working on larger stuff for profit most generally.
That is one reason ($$ and time and time is money) in modern times it's most generally a throw away and replace world instead of trying to repair UNLESS you have the time and can do it for yourself and/or want the re-build experience.
If you find the crank within specs and you get a rod, new, or a used rod from a donor motor then use plastigauge to check your clearance while the crank is on the workbench. (plastigauge is the final check fittament showing you the real world oil clearances and confirms that you have at least the proper fit rod for that crank)

AND don't feel depressed if you put it together and it explodes, even new OEM motors fail.
You then know you overlooked something, like maybe not torqueing the rod bolts or maybe spilled some OLD Milwaukee acidic green beer in the block or you had too much beer while putting it together.