Tight crank gear

2

2speed

Senior Member
In replacing the timing gear with aluminum, I am installing a new crank gear. The new gear is tight. I know they are supposed to be tight because of harmonic reasons.


I was going to deep fry the gear to make it easier to go on, but before I did that I measured things up.


Crank: 1.351"
Old Gear: 1.350"
New Gear: 1.349/1.3485


.001" press fit I get, .002+ is tons, like literally. I don't want to put force the gear on and then have it split or something stupid down the line. Anyone have the drawings/measurements of what everything is supposed to be? Crank snout and gear bore?
 
Heat the gear with a oxy/acet or blow torch. Heat it quite but not enough to show any color on it. It should then slip on, at least part way, then gently pound it on all the way. I made a driver out of iron pipe, with a notch cut out in it to clear the keyway.
 
For applications like this, I wait until my bride is elsewhere, then heat the oven up to 450-500 and put the gear/race/bearing/whatever in for a half hour or so after the temperature stabilizes. Bearings that are pre-greased tend to leave a telltale odor in the kitchen...
 
JayJay said:
For applications like this, I wait until my bride is elsewhere, then heat the oven up to 450-500 and put the gear/race/bearing/whatever in for a half hour or so after the temperature stabilizes. Bearings that are pre-greased tend to leave a telltale odor in the kitchen...
Click to expand...

And experienced Husband! LOL Can't ya put the grease on the crankshaft surface instead? Seems like a helper with 2 pair of heavy leather gloves and a big pair of channel-locks would be handy.
 
I have used the propane powered grill outside to heat things. Avoid pounding on the gear put use a series of bolts and washers to press it on. Pounding may damage the trust bearing in the engine. The ball bearings used for wheelbarrow wheels will avoid turning the gear that has to be carefully aligned. Put the transmission in high gear and put on the parking brake and block the wheels. You can use the pulley instead of a section of pipe.
 

Attachments

  • Bolts.jpg
    Bolts.jpg
    40.4 KB · Views: 16
Last edited:
The new gear looks like it's a cast blank, with a stress riser in the keyway with a sharp corner, doing an almost .003 press fit seems wrong. I realize that heating the gear will make it easier to put on, but I'm trying to find out if the new gear is too tight/not to spec, considering it doesn't match the old gear.
 
I would replace the gear if you think that gear is a cast blank and not machined the concentricity won't be correct you don't wanna find this out once you get the engine assembled and running!
 
Your gear bore should be somewhere in the neighborhood of 1.3745"

Heating the gear is good advice. A CI gear may not change color enough to help you here. Welding supplies sell temperature indicating crayons that work well. As above 400-450 F is about as high as you want to go and should be enough for the gear to slide on.
 
Contact whoever you bought it from and get them to replace it for you

Alternatively, take it down to your local shop and have them bore it to the size you're looking for
 
Yes, 0.0025 seems excessively tight. Cast iron is brittle. I would not chance it. Cast iron will expand if it goes through a heat cycle. You could try heating it to 500 F then cooling it and them re measuring the bore. A few heat cycles like that may expand it enough.

I am breaking in a new antique engine that has a steel cylinder and a cast iron piston. No rings. The instructions say to go through a series of heat cycles to "hone" the piston to the cylinder. Many heat cycles. The piston wears a little but also expands a little. At the end there are mirror finishes on the bore and piston with the correct line to line fit.
 
There has already been one Burtz engine shredded a cast crank gear. Photos should be on the Facebook page.
 
You must log in or register to reply here.
Back
Top