0-300 tear down.

[Tom-D]

Here is the backside view of an O-300 case:

That's actually a very early C-125 case. It works as a C-145 0-300-A and D but not the -B or C

 

[Stan Cooper]

If you have too much slop....the valves won't open all the way....and you'll lose power.

Thank you.

 

[Tom-D]

Right, and based on Kent Felkins' recollection and the O-300 overhaul manual table of limits, that range is .030" to .110".

The clearance with the original pushrods and rockers collapsed after installing the ECi cylinders was ~.120", so I needed a longer pushrod to get the clearance in the spec'd range. I'm not saying the original pushrods wouldn't have worked, but having that extra slop when the specs say it's too much isn't my idea of doing the job right. YMMV.

O-300 Overhaul Manual Table of Limits

When you do this check, and get over .110" Some thing is wrong at the cam to lifter junction, either the cam is too small, or the lifter is too short.To properly correct for that requires a lot more than a longer push rod.And you are right .110" is what the designer wanted as max, but the lifter will expand more than that and take up the slack.
MHO some body removed too much from the rocker arm when they reworked the rocker arm, You did rework the arm when you replaced the cylinder? Because if you didn't the extra .010" you got came from the wear of the rocker arm bushing.

 

[Tom-D]

In auto circles, the semicircle that the bearing sits in on the engine block is called the saddle. The crank has half the bearing surface in the block and the other half in the caps (like a connecting rod).

I've always heard that referred to as the "bearing cap" , like in 4 bolt mainbearing cap.

 

[Stan Cooper]

It seems strange to me that several other CPA members with O-300 powered 172s who switched from Continental cylinders to ECi cylinders all had the same difference in pushrod to rocker clearance; measured before and after switching cylinders the extra clearance was there. To me that says there's a difference between the cylinders. EOT

 

[455 Bravo Uniform]

In auto circles, the semicircle that the bearing sits in on the engine block is called the saddle. The crank has half the bearing surface in the block and the other half in the caps (like a connecting rod).

455-If memory serves the reason a shorter cam chain is needed is that when they align-bore, they take most of the material out of the block side of the journal and not the caps, thus moving the crank centerline higher (closer to the cam). On the flat aircraft engine with the case split vertically, the issue is not present.

Yes, you are correct.

As for the main caps, in big block Buicks, the caps are plenty beefy to take material off, as the weak link is the block webbing where the main bolts/studs thread into. The engine block cracks around the saddle, sometimes right where the main’s oil galley is drilled. I never had to worry about that, never made that much power. They made block girdles as a bandaid and now have a new aftermarket alum block for the boys making 1000+ hp (I stopped at 700hp and stayed below 6k rpm). Glory days...

 

[455 Bravo Uniform]

I've always heard that referred to as the "bearing cap" , like in 4 bolt mainbearing cap.

The 180 degree bottom portion is the main cap.
The 180 degree upper portion in the block is the saddle.

 

[455 Bravo Uniform]

455 Buick block upside down view.

Main bearing saddles with oil hole at the top (bottom in pic).

Thrust bearing goes in the #3 main.

You can see the cam bore (unlike aero, you have to feed the cam through the cam bearings, and the cam bearing is a 360 circle that has to be “pressed” in).

This particular engine made over 550 ft-lbs torque until I swapped it out for another.

 

[Tom-D]

It seems strange to me that several other CPA members with O-300 powered 172s who switched from Continental cylinders to ECi cylinders all had the same difference in pushrod to rocker clearance; measured before and after switching cylinders the extra clearance was there. To me that says there's a difference between the cylinders. EOT

There are a large number of 0-300 that have way too much valve clearance, If there were a speck of difference in design of the ECI cylinders there would be paper on it. (there ain't)

Did you in fact rebush the rocker arm? Many don't they yank one old cylinder, put the new one on with the same old worn out rocker arms and wonder why they have too much clearance?

 

[Tom-D]

The engine that I tore down this week, had 1100 hours since major by G&N the lifters were flat even dished a bit, cam was a reground at major, lifters were reground at major. and the check measured between .080" and .090" and the rocker arm bushing was .0015? out of round.
So knowing there is no difference between TCM cylinders and ECIs tell me why your getting .120" inches dry tappet clearance?

 

[Stan Cooper]

There are a large number of 0-300 that have way too much valve clearance, If there were a speck of difference in design of the ECI cylinders there would be paper on it. (there ain't)

Did you in fact rebush the rocker arm? Many don't they yank one old cylinder, put the new one on with the same old worn out rocker arms and wonder why they have too much clearance?

I don't think we rebushed the rocker arms, but that was thirteen years ago so I'm not sure.

 

[Tom-D]

View attachment 61717

Big ugly dirty paper weight

 

[BiffJ]

Frank- it’s not journals (not the cam, not the crank) it’s the saddles (the case where the cam and crank and/or bearings sit) that when align (line) bored (honed) brings the cam and crank closer.

Like Dan Thomas noted and pictured, nothing changes the distance between the shafts so no change in gears other then replacement for wear like any other gear. Line boring doesn't move the hole, it only opens it back up after facing off the mating surfaces of the case.

Frank

 

[455 Bravo Uniform]

Like Dan Thomas noted and pictured, nothing changes the distance between the shafts so no change in gears other then replacement for wear like any other gear. Line boring doesn't move the hole, it only opens it back up after facing off the mating surfaces of the case.

Frank

Yes, I was wrong.

 

[Tom-D]

Yes, I was wrong.

Not wrong, didn't know, there is a difference.

I once took an engraver pen and placed a line of dots on the case seam on both sides of the case below the front main bearing, and sent the case to Divco. they came back the dots were still there. Two cases prior to this leaked like a sieve. I then changed to Chuck Ney he did them very nice. then I found he was sending them to Crankcase services, So now I do too. (Chuck Ney has passed)
So,,, what doesn't kill ya should make ya smarter. Ya live you learn. Hopefully.

 

[flyingbrit]

case will go out to be reworked, (lapped and line bored)

How do you determine that the case needs lapping?

 

[Tom-D]

How do you determine that the case needs lapping?

I simply have it done as a precaution.
I do not have the equipment to determine if it is needed or not or not.