Questing about a flywheel casting issue.

[Clarksville Don]

I am working on a Red Wing water cooled kit from PM Research. I had an issue getting a drill to run true when drilling the flywheel hub prior to boring and reaming. On the second flywheel I noticed a strange pattern on the face of the hub after I took a facing cut. There is a light colored disk about 70% of the diameter of the hub that is offset from the center of the hub. there are 6 small diameter dark spots inside of the light area. If these spots are of a different hardness it could explain the issue with drilling. I asked PM Research and they stated it was from part of the casting process but did not provide any explanation of the process that gives this issue. Does anyone have any info?

 

[johnmcc69]

Weird. I wonder if originally they had a core there & was out of location (obviously), removed the core on the cast flywheel & "filled" the cored hole in afterwards...

Dunno....

John

 

[Jack3M]

Bizarre, if it were not for that perfect offset circle I would have said hard spots from chilling.
Coming back to your drill bit wandering, I find that using cobalt bits will resolve that unless there are very unequal hard spots.

 

[WOB]

If it is some sort of chilled iron from making the casting, it will likely be impossible to machine it with HSS tools. A plunge cut with a carbide end mill will make the initial hole and then a carbide boring bar will allow you to size the hole accurately. Reaming should not be necessary.

WOB

 

[Clarksville Don]

If it is some sort of chilled iron from making the casting, it will likely be impossible to machine it with HSS tools. A plunge cut with a carbide end mill will make the initial hole and then a carbide boring bar will allow you to size the hole accurately. Reaming should not be necessary.

WOB

WOB
Thanks fo your input. I do have a small carbide tipped boring bar and used it to finish the bore of the first flywheel. Your suggestion of starting with a carbide end mill sounds good. Thanks
Don

 

[larryg]

I think I'd be inclined to reverse the flywheel in the chuck and face the other side to see if the 'plug' goes all the way through. It does look way to round to be a casting flaw.

lg
no neat sig line

 

[Philipintexas]

Do the “circles” correspond to, or align with the spokes? Could they be some kind of harmonic caused by them????
I built that same engine and all my castings were of the highest order.
Either that or they are caused by the same thing that creates “Crop Circles”! Really strange.

 

[Jack3M]

I think I'd be inclined to reverse the flywheel in the chuck and face the other side to see if the 'plug' goes all the way through. It does look way to round to be a casting flaw.

Interesting point. Once I screwed up a flywheel so I made a plug for it that was a press fit. This reminds me of that.
I will be most interested to hear how the hole process went and if that also shows on the other side if faced. Very curious one here indeed.

 

[TonyM]

Did you flip it round and skim the opposite side to see if its the same

 

[jlchapman]

I had the same question earlier this year. So this was the response from PM Research:

That is how the casting is made. The center core is placed in there to keep the flywheel from collapsing at the foundry. That is a good flywheel.

Jerry

 

[Clarksville Don]

Thanks for all the input. I did flip the flywheel and do a face cut and the pattern does go through. It does not have the 6 small dots on the second side (first photo). I also faced the first side to final size by taking another .o25 facing cut. The pattern looked like it was starting to go away?( second photo). I did manage to get a 5/16 drill through the hub with a small amount of wobble. I trued the hole by using a 3/8 end mill and will now be able to bore to final size.

Don

 

[TonyM]

I had the same question earlier this year. So this was the response from PM Research:

That is how the casting is made. The center core is placed in there to keep the flywheel from collapsing at the foundry. That is a good flywheel.

Jerry

That's interesting.
I guess it is just a PM solution for a specific problematic mould although I would assume there is a big risk of hard spots around the join.
It would be nice to know if the core showed up on the casting before machining as I can't quite see how it would be located in the mould unless it does.

 

[Clarksville Don]

The pattern could not be seen before the facing cut. From the way drills and the end mill reacted, there were hard spots in the casting.
Don

 

[TonyM]

OK so I am not familiar with casting processes. It would be great if someone anyone who is knowlegeable about casting could throw some light on how this 'included core' process might be done and why it doesn't show up externally on the casting?

 

[Philipintexas]

Ditto to that! My understanding of a “core” is that they usually leave a recess in a part. IE: the water-jacket of a Corliss

 

[MachineTom]

Odd that they left a piece to hold the 2 mold halfs apart. As the flywheel is split, would not seem to be needed.

 

[Fogey]

I had the same issue in my Redwing. When facing the hub there was no doubt something was in there. Harder than Hades! Changed to finish with carbide. Also spoke to PM at the NAMES show, they gave me the same answer about the core in the casting. It looks to me like they placed some odd metal in the mould as filler.

 

[tjwal]

My guess is that it serves as a chill so the hub cools quicker. In general when casting it is best to have the parts of the mold furthest from the sprue to cool first.