Ironhead ‘72 Pinion gear question

[NP72Iron]

Hey all,
I’m building up a ‘72 XLCH motor and pressed on the pinion gear today, but it does not fully seat against the spiral gear when it’s 5/16” outside of the cam case mid-line.
When I got the motor the pinion gear was installed, but not in the correct timing position, so I had to remove it and install in the correct position. Prior to me removing it, the gear was all the way against the spiral gear. So is it okay for there to be a gap between the two as shown in the photos or should I press it all the way back up against the spiral gear?
Thank you in advance.


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[Scuba10jdl]

Yes, that's ok. Use the 5/16" measurement, as that's the important measurement to center the pinion for the cam drives.

[NP72Iron]

Thanks [mention]Scuba10jdl [/mention]!


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[72 Ironhead XLH]

I beleive all the cam bushings are all the same height so does the protruding pinion affect that dimention?

[brucstoudt]

your picture shows the gasket still in place?you're not measuring 5/16''off the gasket face are you?

[sungod]

Originally Posted by brucstoudt

your picture shows the gasket still in place?you're not measuring 5/16''off the gasket face are you?

Bingo!

[NP72Iron]

Originally Posted by brucstoudt

your picture shows the gasket still in place?you're not measuring 5/16''off the gasket face are you?

Good catch, though I didn’t measure the gasket, I measured from just above it.


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[mrmom9r]

The pinion gear can't be "out of time".

It only goes on one way.

You cannot leave a gap between it and the spiral gear as that will affect the

breather timing.

[needspeed]

Hi Mrmom, I never thought I would disagree with you on anything related to engine assembly, but In this case I do.

Yes, the position left to right of the spiral gear does affect breather timing. As you know, altering it's position is one of the ways to precisely dial in the opening event with a degree wheel.

Normally it's just a matter of aligning the dot in the slot with the flywheel advance mark showing. From one engine to another the dot doesn't always end up dead center in the slot. Given manufacturing tolerances in the gears and parts, the average builder doesn't know whether the timing is best with the gear forced all the way towards the flywheel or taking up the endplay the other way, with it pressing against the pinion gear set at 5/16 proud to the case. That's where it will always be with the engine running.

IF the dot/slot lineup happens to look better in that position it makes sense to run it there.

So which position is the breather timing more accurate? How would anyone know without checking with a degree wheel.

The OP can do it what ever way he chooses to. I 'm sure it will run fine either way.

For me, I put the pinion gear on per the manual (5/16 out)and accept that there will be spiral gear end play.

[NP72Iron]

Originally Posted by mrmom9r

The pinion gear can't be "out of time".

It only goes on one way.

You cannot leave a gap between it and the spiral gear as that will affect the

breather timing.

Thank you for your reply. I should clarify…the oil hole was not in the correct position when the cam gears were all lined up, thus I needed to remove the pinion gear and line everything up correctly.

I’ve got a couple of guys telling me that a gap between the cam gear and the spiral gear is okay, and now you’re telling me it isn’t. I’ve searched for an answer in my HD service manual, in the Clymer, and online. All I’ve been able to find out is that the face of the pinion gear is supposed to measure 5/16” out from the case gasket surface face which is what mine measures. Can anyone else weigh in on this?


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