Over Bore on a K301A?

XanderGear · #1 07-27-2011, 11:13 PM

I have a '67 122 with the stock K301A. The cub has had a lot of use over the years (I’ve been mowing with it for over 20 years myself) and is still a great machine. Over the last couple years I have grown accustom to mowing in a cloud of smoke. I think I have two options. One, bore and rebuild it. Or (hopefully) two, pull the head and check it to see it its warped.

The last time I had the head off I saw that the piston was stamped .030. My first question is, can I bore it out again? Is there a larger piston/ring set available? If so where? If not, what options do I have for a over bore?

My second question is, if the head or deck are warped how can I check to see if they have ever been fixed in the past and how much is left so I don’t take too much off?

Thanks

R Bedell · #2 07-28-2011, 06:52 AM

Boring options: .010", .020", & .030"

Lay the head on a piece of heavy sheet glass and check to see if there are gaps. I highly doubt the deck of the motor is warped but one could check with a piece of glass also or a good straight edge.

A Machine Shop could true up both if not too severe.

ol'George · #3 07-28-2011, 07:04 AM

If you have a real affection for the block, most can be re sleeved to standard bore.
I once found an engine that had been “rebuilt” and burned oil quite badly.
Upon inspection, I found someone had installed std rings on a .010 over bore/piston.
Needless to say a new set of correct size rings solved the problem. It might be worth a look.
Also the bore/piston might be ok and just rings will cure the problem, or alleviate it substantially.

XanderGear · #4 07-28-2011, 10:15 AM

Thanks Guys, I was figuring on checking the head that way and I'll take a look at the rings. Is there any way to figure out how much or the head has already been removed? Do I have any options for boreing it more than .030 or are the cylinder walls just not thick enough?

ol'George · #5 07-29-2011, 08:24 AM

You could probably go a little more than .030 but no piston is available unless custom made ----read, big $$$$
A lot of old engines made before 1960 could safely go .125 over,--- BTDT

Now if it were mine, I would remove the head and look @ the bore,
if I see no big scores or other obvious problems, scuff it lightly with a deglazer and install new rings.
That will reduce the oil consumption.
Of course while it is torn down you want to check the rod/crank condition as well as other notable items etc.etc.
As far as the head gasket, if it isn’t blown or leaking, replacing it will not improve the oil consumption problem.

jsoluna · #6 07-29-2011, 09:15 AM

I have the same problem with mine, and when I pulled the head, I could move the piston side-to-side slightly in the bore. Looking closely at it, I could see the rings between the wall and piston.

Still runs like a champ, just have to keep throwing oil at er until I can get the money for a rebuild/replacement. I have found a that replacement engines can be almost as expensive, if not more, than a good rebuild.

Expect 450-500.00 for a good rebuild.

westofb · #7 07-29-2011, 09:17 AM

The two I've been in (301 & 321) would not have much room for boring very much. The cylinder wall that extends downward toward the crank is pretty thin. The 321 I am rebuilding was in the same shape as yours, .030 piston already in it, and bore was worn. Mine is at the machine shop right now, it is being sleeved back to standard bore.

XanderGear · #8 07-29-2011, 02:18 PM

If it is too far gone for rings to help... how much could I expect to spend resleeving it?

ol'George · #9 07-29-2011, 03:33 PM

Quote:

Originally Posted by jsoluna

I have the same problem with mine, and when I pulled the head, I could move the piston side-to-side slightly in the bore. Looking closely at it, I could see the rings between the wall and piston.

Still runs like a champ, just have to keep throwing oil at er until I can get the money for a rebuild/replacement. I have found a that replacement engines can be almost as expensive, if not more, than a good rebuild.

Expect 450-500.00 for a good rebuild.

It is normal to move the piston slightly in the bore as they run maybe .005 clearance and the piston does rock on the pin making it look more.
but granted if you are cosuming oil, things ar worn a bit.
A precision measurement is the only way to tell what you really have.

ol'George · #10 07-29-2011, 03:41 PM

Quote:

Originally Posted by XanderGear

If it is too far gone for rings to help... how much could I expect to spend resleeving it?

Best to talk to a reputable machine shop, not a "down the street type fixit shop" also if you give them a clean empty block it will be less $$$ than if you are paying a wrench to take it apart/clean it.
Prices do vary according to location and they welcome such work in the off season.