The International Cessna 170 Association

I just had my O-300A rebuilt. After getting it hung, I notice the clearance on the oil quick drain valve is no longer there.
So you can no longer push the quick drain up to lock it open. It appears that the engine is now a little more aft then before.

The engine shop did replace the engine case during the overhaul. Can anyone provide an opinion on how this might have happen or a fix? I would prefer not to go back to an oil plug.


See attached pictures (right side has no clearance)

You gave a few clues. Replacing engine crankcase halves is major.

Does your current engine still have the orig data number plate attached?

I will hazard a guess as to what may have happened.

The split halves of crankcase were milled flat because of slight fretting. Then the halves were joined and an Align Bore precision performed to restore the original clearances for Crank and Camshaft assembly.

Now your engine may be hung .020 off center from where it spent the last 50 years!

I may be 100% Wrong Just an observant bystander!

Otis, it’s not clear to me in your pic what the obstruction is. Can you clarify this?

George, it is the back crossbar. See picture.

Gerry,
I would look closely at how the shock mount bushings, p/n 23411, are installed. Were new ones installed with the overhaul? Are the front ones sagging? My front ones measures 0.174" between the shock mount flange to the adjacent engine mount tang. The flange should be on the bottom. Are the front bushing clamped in too low or the back ones too high? The only other thing I see that would affect the position of the drain to the mount crossbar is how the engine mount brackets (fig. 3-20 & 3-29) are mounted to the case. Does someone here know if there is any play which would allow the brackets to be mounted or rotated slightly further aft? I'd be surprised if there was play.

I have the same quick drain, the knurled collar is rotated, pushed up and rotated to the lock position. In your case, you're saying the tubing prevents the knurled ring from happening and if so, you can no longer split hairs and make it work or previously there was much clearance ?

First, the quick drain had clearance before the rebuild.
New shock mount bushings were installed at the engine shop.
I will check the flange location tomorrow. Just got back in town.

Thank you for your input.

Gerry

Gerry,
I know it doesn't get to the root of your problem but if nothing else fixes the clearance problem it looks to me like the Safe-Air S1000 may have a little more clearance than your oil drain valve.

I don’t have my engine manual with me and I can’t look at my plane so this is just a guess but, could the motor mount legs be reversed side to side or front to back and locate the engine further aft?

I thought the same thing Richard but I couldn’t fathom a shop doing that, the p/n’s are embossed in large numbers on the side each mount leg.

The front and rear motor mounts have different bolt patterns so it is not possible to swap the front to rear and the left and right are mirror images it shouldn't be possible to swap left to right.
Took this picture my drain valve yesterday for comparison. The blue knurled piece has about 3/4" clearance from the cross bar.

As stated, the motor mounts can not be switch. The engine shop said “there may be a slight geometrically difference
than the original engine block. The sump is the same one.”

My quick drain is aft 1/2” (+ or -) from where it was before the overhaul. We are going to install the original plug and move on with the install.

Should we have any concerns?

If your engine is aft 1/2", will the spinner clear the cowl would be my question. Also how does this effect CG and off course how are you going to document that change? Is the entire engine back 1/2"?

I really can't see how this can be. The mounts are keyed to the case halves. They can not be installed incorrectly. There is no machining that should or could have taken place to move the location. You can not bolt the sump on 1/2" back cause the mount holes won't line up and of course it is fitted to the accessory case which is flush to the aft of the case.

There is something else amiss here.

That’a Great pic Bruce ; maybe it’s dimensional check time for the mount.

lowNslow wrote:The front and rear motor mounts have different bolt patterns so it is not possible to swap the front to rear and the left and right are mirror images it shouldn't be possible to swap left to right. ...

Karl, while what you say is true, there are only two leg part numbers. The right front is the same as the rear left (p/n 40043) and the left front is the same as the right rear (p/n 40044). I loosened the three bolts holding the front right leg to the case on my engine to see how much play was present. I got approximately 1/16” fore and aft play — not enough to cause the difference Gerry is seeing.