Lycoming GT/226cu in motor + other 8 in lines

[John Gelfer]

I know this motor was used in the 1927 Auburn model 8-77. The 8 cylinder Lycoming 4HM, 4H, GS & GT were used in other Auburns from '26 through '29. I have the GT in my 1928 Gardner. I'm trying to locate the TDC mark on the flywheel through the peep hole near the starter at the rear of the engine. I'm seeing many numbers on the flywheel like 15, 27, 18, 27, 36, 45. There may be more, but it seems like TDC is where the 45 shows up. Isn't there supposed to be a punch mark or arrow to indicate TDC? I want to make sure I have it right.

[John Gelfer]

I figured it out using the "bubble method". I put a fitting in #1 cylinder, attached a hose, and put some soap suds on the end of the hose. As it came up on compression, I watched the size of the bubble growing. If you go to far, the exhaust valve opens and the bubble deflates. After several tries, I was sure where TDC was. The number 18 was showing on the flywheel peep hole. This still makes no sense, but at least I now know where the TDC mark is.

[Curti]

John, I am most familiar with the 1934 - 1936 Auburns. However the 1/8 means cylinders 1 & 8 are on tdc.

Prehaps the other numbers are from a replaced ring gear.

I have never heard of the bubble method, interesting.

[Guest Silverghost]

The flywheel marking positions sound odd indeed !

Do you think the flywheel was removed from the crankshaft in the distant past and re-installed in the improper position ? Perhapps to be resurfaced or to have a ring gear replaced ?

There should be a TDC mark I would think ?

[mdsbob]

I'm seeing many numbers on the flywheel like 15, 27, 18, 27, 36, 45. There may be more, but it seems like TDC is where the 45 shows up. Isn't there supposed to be a punch mark or arrow to indicate TDC? I want to make sure I have it right.

As Curt mentioned the 18 would means those cylinders are on TDC...However, they both can't be on TDC at the same time. When either the 1 or 8 is on TDC the other cylinder (1 or 8) has just finished the exhaust stroke. It takes one complete revolution of the crankshaft to get the other cylinder to TDC.

The other 2 number sequences 27, 45, etc. would be for the other cylinders. I see you have 5 number sequences listed in your post, I believe there should only be four, 18, 27, 36, 45 or something similar to that. Also, the number sequences should be a quarter (1/4th) of a rotation on the perimiter of the flywheel from each other. It will take two rotations of the crankshaft to cycle each cylinder to TDC.

Isn't there supposed to be a punch mark or arrow to indicate TDC? I want to make sure I have it right.

Make sure there isn't another location for viewing these numbers, it could be that another peep hole is under some bracket or something that is bolted to the flywheel cover, block, etc. And, yes I think there should be some sort of pointer.

I was sure where TDC was. The number 18 was showing on the flywheel peep hole. This still makes no sense, but at least I now know where the TDC mark is.

This is indicating that you have No. 1 cylinder @ TDC. Move your bubble tester to No. 8 cylinder and with one complete revolution of the crank you should get the same results on No. 8 cylinder.

You can use your firing order (starting @ No.1 cyl.) and with 1/4 turn of the crankshaft progress through TDC on each cylinder.