Cylinder Honing 1960 Lark

[Mossman747]

I’ve checked the workshop manual and can’t find the answer for this.  What is the recommended grit for honing the cylinder in a 1960 40 HP Lark?  I am assuming but can’t confirm that the rings are cast iron which would call for something around 180 grit in a 4 stroke engine.  Whether that is different with a two stroke I can’t confirm.  I would appreciate some insight from someone who has done this before with good results.

 

Thanks in advance

[Bob Wight]

I’ve typically used a 240 grit flex hone on my motors with good results.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[Mossman747]

By flex hone do you mean a ball type hone or the kind with 3 stones on spring arms?  I am using an adjustable precision hone to take about .002” of oblong wear out of the cylinder in the process.

The odd thing is, the cylinder seems to be about .0025 to .004 undersize according to the manual which lists the bore size at 3.19 in the specification section.  Earlier in the textural description portion of the manual the bore is referred to as 3-3/16 which what I am reading as the larger measurement in the cylinder so I think I can still true it to 3-3/16.

[Bob Wight]

I’m referring to a ball type hone.   I generally use these just to take the glaze off a cylinder, but a ball type hone will not correct an out-of-round cylinder.  Perhaps the bore size of 3.19 listed in the manual might have just been rounded up from 3-3/16 (3.1875).

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[Pondrocket]

Mossman747,

I would agree with Bobw at 240 but check with your ring manufacturer. I also use a precision adjustable hone & get it close to finish size then finish off with a ball hone as bobw states to get the required cross hatch & finish dimension…

Travis
AOMCI VP Communications
AOMCI Webmaster
webmaster@aomci.org

[Bob Wight]

Finishing up with the flex hone also does a good job of taking off any rough edges around the cylinder ports.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[Mossman747]

I’ll pick up a ball home for finishing, I would have thought a ball hone would chew up the ports but it sounds like that’s not the case.  The rings are NOS OMC parts so I’m not sure if I can get any information from the manufacturer regarding ring composition and required surface finish unfortunately.

[fleetwin]

I am confused about your cylinder measurements. I really don’t think the bores are “undersize”. Please do not attempt to hone/bore the cylinders to the proper dimension. Make sure you have the proper service manual, and check your measurements again.

[Mossman747]

In the engine specification sheet in the service manual the bore is listed as 3.190.  My cylinders measure out at 3.1875 measured left to right and about 3.186 measured top to bottom, so very slightly out of round.  Even in it’s worn state these measurements are undersized based on the stated dimension of 3.190 in the specification section of the manual.  However, in a different part of the manual buried in a paragraph of text the bore is stated as 3-3/16” which seems more correct based on the measurements I am reading.  My plan is to use the rigid hone to true the bore to my larger measurement of 3.1875 then finish with a ball hone and nylon honing brush for a plateau honed finish at the smaller of the two dimensions stated in the manual.

[Tubs]

I read your post and had some thoughts.
Being able to precisely remove the material from
your cylinder, as you have describe using hones,
is unrealistic. By the time you’re done, including
the seating of the rings wearing the cylinder
smooth again its likely you have removed .002 or
.003 from the cylinder increasing the bore size
by .004 to .006. How are you going to make the
piston bigger? Back in the olden days, when new
replacement parts weren’t so accessible, knurling
the skirt was how we compensated for this.
I’m just another guy on the then internet so use
your best judgement.
Below is from Otto Gas Engine Work.
A piston ring manufacture.
Tubs
.

Honing-
The other thing people overdo is hone. They want to see a
pretty 350 chevy cross hatch pattern but that is not necessary in
our old engines. You are grinding away precious cylinder wall
material. The extra piston to cylinder wall clearance will allow the
piston to rock around in the cylinder and will break the seal of the
rings. If you can’t resist the extra honing get a piece of emery
paper and do it by hand. When your arm is tired you know that
you are done.
.

A "Boathouse Repair" is one that done without having tools or the skills to do it properly.

[Author]

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