446 Engine

[Vivala446]

I think probably the situation is that I bit off more than I can chew and now I need to consider the financial aspect of things. What’s going to be A.) cheapest, and B.) quickest to get the machine running so I can take care of my property

[Eugen]

Your options are roughly either re-power the tractor, or fix this engine. If you can find a good 10-14HP Kohler from another Case you'd get at least an engine that you can use the attachments you have because the engine comes with the right shaft for the PTO.

To fix the engine you have, without some tools, is next to impossible. As I said, you need to find out the state of the engine, dimension of the cylinder bore, dimension of the pistons you got, and what shape the rings are in. I think everyone around here agrees that a proper rebuild of the Onan B43M is rather expensive, compared to a Kohler for instance. This is the reason I myself got only a Case 446 and several Case tractors with the Kohler 14HP.

From what you've said so far it seems that the most likely scenario is that the pistons you got now are undersized for the cylinder bore you have. A rough measurement without taking the engine out would be to take one head off, bring the piston all the way up, and see what a feeler gauge says for clearance between piston and cylinder. If it's way big you'll know for sure these are not the right pistons.

[Harry]

I'm a little late coming to the party Vivala446. From what I just read you replaced the pistons from some you purchased from Ebay. You also said you read up on how to do things before you jump into doing it. So, my question to you is did you check the ring gaps on the rings in the cylinders before installing them?
If everything is the same as before you replaced the pistons there is a leakage somewhere in the cylinders and a leak down test would confirm where, as one of the members suggested.

Keep the Peace
Harry

[Spike188]

@Vivala446 Please don't step on your bottom lip and walk away. You have been peppered with a lot of information in the preceding post.

Of all the advice given @DavidBarkey is my choice of where to start. You have had the engine a part so doing an in-frame test should be clean and easy. Here is Dave's advice in a step by step form.

1) Take both head tins off
2) Remove both spark plugs
3) Remove breathe assembly and air hose to fan shroud
4) Look down large hole in shroud with flash light , rotate crank shaft to top dead center marked on flywheel (fan) ,
5) Pull dip stick out
6) Open choke and throttle,
a) Using compressed air and blower with rubber tip to seal around the plug hole, blow air into a spark plug hole and take note of where the
air comes out on that cylinder.
- ring problem, air will come out dipstick tube.
- head gasket, air will come out where head and block meet .most likely the top
- valve problem, air will come out carb or exhaust or both
b) Rotate flywheel 1 turn, apply air pressure to the second cylinder and repeat step (a)

The cylinder that is on compression stroke will leak air out of the fault and if not on compression stroke it will leak out which ever valve is open .

Note: Engine can be turned over by engaging the clutch and turning the pto pulley

If anyone has any more steps to add please chime in.

Spike.

[Vivala446]

I had a stroke of good luck last night… I found that I had set one of the old pistons and rods that I took out of the engine— the one that was in good shape out beside my garage. It had STD stamped in it. I’m going to verify probably this weekend, but I feel just by looking that the replacement pistons I bought are in fact a little smaller. If that’s the case that could be the issue.

[DavidBarkey]

http://www.enginemastersinc.com/onanreb ... mation.htm

Onan twins only come in 2 bores sizes Small block 16-20 hp and BIG blocks 24-25 hp . The stroke changes the hp. If the pistons coming out are std. over sized could not go in the hole . at this point I feel since it ran on one cylinder prior and the pistons came flush with the block . The valve system not touched . We are down to 2 things . The head gaskets on backwards (almost did it my self once) . Or the rings in the "new pistons" are stuck in the grooves .

Leak down test will tell all

Dave

[Eugen]

Dave, did you forget the BF-MS?

16HP twin Onan BF-MS bore is 3-1/8
16HP twin Onan B43M bore is 3-1/4



The good news is that you found the old piston. All hope is not lost!

[Vivala446]

Upon review of my receipt for the “new pistons”, they were for a BF-MS. My engine is a B43M

[propane1]

Ah ha, now we’re getting somewhere. You’ll get it fixed now. Get the right pistons and your in business.

Noel

[Eugen]

Mystery solved! Hey, it could be worse, right?

Now at least you can make some more informed decisions. You know your bore is STD, and that you need B43 pistons. Wish you had joined us sooner before you did all the work and got the BF-MS. Oh well, as my wife says often, sometimes you win and sometimes you learn.