Rebuilt engine hard to turn over, but then loosens up?

[Tommy Mckeown]

If the engine is not hard to turn with the plugs pulled out your problem has nothing to do with the bottom end or anything attached to the engine. It's a compression issue. Either an exhaust valve is not opening when it should or an intake valve is not opening when it should. (think compression release)

 

[TobyU]

I'm the OP.

You really need to read the posts from the beginning. As I've state three times already the problem has been solved.

I replaced #1 connect rod and the engine is back in the mower and running.

Bob

Now this confuses things even more. Unless you had the number one connecting rod somehow installed incorrectly or had a two flipped over and placed in that spot or something weird like that there's no way changing a connecting rod would magically make an engine that's hard to turn over start turning over easily and running properly.
If the number one rod snapped which is all too common when these twins run down even a touch below the ad mark and sometimes even in the safe area then it would be easier to turn over or occasionally but turn over at all due to parts hitting inside.
But the statement that you tried a connecting rod and it's fine now is odd.

 

[Tom O']

I have a JD D140 lawn tractor with a B&S 22 hp V Twin engine. I just over hauled then engine and replace the rings because of oil loss. I reinstalled the engine and cranked it over a number of time trying to start it. Wouldn't start got that figured out and started it and ran for a while at varying speeds to break it in. I tried to start it yesterday and it wouldn't turn over. Thought the battery was low on charge. Put a booster battery on and it would crank over. To the top off so I could get to the flywheel. I put a socket on it and it was hard to turn over for a couple of revolutions then got easy. Cranked it over and it started right up. Today it did the same thing. Runs good once I get it started. Any suggestions on what I should do? The first thing I thought was I got the wrong rings, but the end gap was within specs and it cranks over easy after a couple of revolutions. Is it just that tight and will loosen up over time?

Bob

Possibly try adjusting the carb idle speed and mixture adjustments

 

[Hammermechanicman]

 

[unioncreek]

There are a few concerns that I have. 1) did you fit an oversize ring? If you did, did you deglaze the cylinders with your ring gap being equal at the top, middle and bottom. 2) if you did number 1 correct, are the timing marks lined up correctly on the crankshaft and the camshaft? 3) if 1 and 2 are done correct, did you set the values just after the compression stroke (so at the beginning of the power stroke) on each cylinder? You might have one cylinder correct, but incorrect on the other cylinder. The fact that it runs, tells me that you did 1 and 2 correct, but your valves are not right

1) No to oversize rings, cylinder measurements didn't warrant it. Cylinder was honed. Rings endgaps we're equal top to bottom.
2) Timing marks were lined up, that's not hard to do.

Procedure for setting the valves were the same for both cylinders according to the B&S repair manual.


If people would read the entire thread they would see that the engine has been fixed and back in the mower and running like new.

 

[TobyU]

1) No to oversize rings, cylinder measurements didn't warrant it. Cylinder was honed. Rings endgaps we're equal top to bottom.
2) Timing marks were lined up, that's not hard to do.

Procedure for setting the valves were the same for both cylinders according to the B&S repair manual.


If people would read the entire thread they would see that the engine has been fixed and back in the mower and running like new.

And if the forum wasn't set up or displayed and or emailed notifications oddly on mobile device..... A we wouldn't have this issue.

 

[electech2]

Not terribly familiar with this particular engine but, in the days gone by, Briggs Connecting rods could be installed upside down and would cause this problem. There was a small projection on the end that goes inside the piston that must face the bottom of the engine to prevent the rod from dropping at an angle to cause binding. Installed correctly, the projection would insure that the rod remained straight. I don't know if that is even possible with this engine.

 

[Minguen]

I had a similar problem with my 20 hp v twin when starting from rest. I thought it was the battery too, but I checked valve clearances and they were too tight. Adjusted to spec. and not had any issues since.

 

[unioncreek]

there's no way changing a connecting rod would magically make an engine that's hard to turn over start turning over easily and running properly.


Read the entire post and you will see that the connecting rod was over torqued.

there's no way changing a connecting rod would magically make an engine that's hard to turn over start turning over easily and running properly.

And yet that exactly the way it turned out. The old rod had a clearance of 0.0015 and when torqued the rod was would not move on the cranks. The new rod clearance was 0.002" and moved freely on the crank. I put Dykem on the rod and torqued it down to 50 in-lbs so I could move it a little. There was only shiny spot the size of a pin point that was shiny and it could have been a air bubble.

All I know is I installed a new rod and the engine is running good started up the last 6 time I tried starting it over three days.

And yes the original rods were installed correctly.

Bob

 

[TobyU]

And yet that exactly the way it turned out. The old rod had a clearance of 0.0015 and when torqued the rod was would not move on the cranks. The new rod clearance was 0.002" and moved freely on the crank. I put Dykem on the rod and torqued it down to 50 in-lbs so I could move it a little. There was only shiny spot the size of a pin point that was shiny and it could have been a air bubble.

All I know is I installed a new rod and the engine is running good started up the last 6 time I tried starting it over three days.

And yes the original rods were installed correctly.

Bob

Do you have a history with this engine? You simply can't have an engine that's running fine for 3 years let's say and then it gets hard to crank over and then you find the rod clearance tight and then change the rod and it's okay.
The only way this could be possibly possible is it it had been around the world and that rod was starting to weld itself to the crane but then you would have said and should take the metal off the crank with muriatic acid or whatever else and normally this wouldn't occur anyway as normally just to continue well the metal together and snap the rod.
I always said if you do this that long enough you will find something that's not possible that has occurred right in front so never say things can't be certain ways but this certainly doesn't make sense.
And frankly all this is way too Overkill and in debt and sounds like an engineer is doing it.. lol.
Changing comes my way, I simply see if it's mechanically sound with an external fuel source and if it runs or if it has been then I don't worry about that. I'm never going to turn it to the internals of it unless it snapped a rod or something like that and even then it's not worth it because I can just swap something else more quickly and cheaper.
I'm never going to bother to use plastic edge or two micrometer a rod on a mower.
Torque wrench is fine but anything past that is overkill.