Author Topic: McCoy .35 RH crankshaft-case bearing clearence fit????? (Read 1101 times)

frank mccune · « **on:** February 23, 2019, 02:39:44 PM »

Hello All:

How tight should the above fit be? I am attempting to fit a"new" crankshaft to this engine but it will not enter the case with ease after polishing with 1200 paper. I do have a bit or fine lapping grit that I may use but what I need to know is how freely must the crankshaft spin in the case to be proper.

Tia,

Frank McCune

Dan McEntee · « **Reply #1 on:** February 23, 2019, 03:01:00 PM »

Make sure that there is no burr or "mushroom" on the end of the crank shaft first. Measure the old shaft. If it's clean. measure the new shaft and the bushing to see what you have. Given the nature of McCoy quality control, I'm surprised that it doesn't fit. Try the new shaft in another engine if you have one. Some fine lapping compound, or gentle reaming may be in order, but I'm still curious as to what things measure out at.
Type at you later,
Dan McEntee

RandySmith · « **Reply #2 on:** February 23, 2019, 04:40:52 PM »

Quote from: Dan McEntee on February 23, 2019, 03:01:00 PM

Make sure that there is no burr or "mushroom" on the end of the crank shaft first. Measure the old shaft. If it's clean. measure the new shaft and the bushing to see what you have. Given the nature of McCoy quality control, I'm surprised that it doesn't fit. Try the new shaft in another engine if you have one. Some fine lapping compound, or gentle reaming may be in order, but I'm still curious as to what things measure out at.
Type at you later,
Dan McEntee

You will also need to check the bushing in the case for a ding or ring around the edge, Easy way to check if this is a problem is put the crank in the front to check the fit, Rear should be the same, If it is OK then you will need a good bit of lapping to fit, Use at least .002 thou clearance minimum to start

frank mccune · « **Reply #3 on:** February 23, 2019, 06:06:40 PM »

Hello Dan and Randy:

Thanks for the prompt and informative replies.

I measured the two shafts and found that they are different in diameter. When measured on the end where the threads begin the new one measured .4380" and right in front of the intake port it measured .4381". The original shaft measured .4375" at both places. I interpret this to indicate the shaft has a bulge of .0006" in front of the intake port. I did insert the shafts into the case from both ends to determine where the problem may lie as Randy suggested.

I guess that the best method to remove the bulge is to place the shaft in a chuck and apply some fine paper and oil. However, I doubt that I have a chuck that will hold the shaft true enough for this process to be accurate. Perhaps a light lapping to the case may solve the problem, but I will be using the bulge to lap a "ring" in the crankshaft bearing at the tight spot. On the other hand, what would the harm be if there is a ring in the bearing?

What grit of paper would you suggest for this polishing of shaft? The lapping compound is a powder that is mixed with oil to lap pistons to cylinders. It works very well.

Be well friends,

Frank McCune

Brett Buck · « **Reply #4 on:** February 23, 2019, 09:11:03 PM »

Quote from: frank mccune on February 23, 2019, 06:06:40 PM

I measured the two shafts and found that they are different in diameter. When measured on the end where the threads begin the new one measured .4380" and right in front of the intake port it measured .4381". The original shaft measured .4375" at both places. I interpret this to indicate the shaft has a bulge of .0006" in front of the intake port. I did insert the shafts into the case from both ends to determine where the problem may lie as Randy suggested.

I guess that the best method to remove the bulge is to place the shaft in a chuck and apply some fine paper and oil. However, I doubt that I have a chuck that will hold the shaft true enough for this process to be accurate. Perhaps a light lapping to the case may solve the problem, but I will be using the bulge to lap a "ring" in the crankshaft bearing at the tight spot. On the other hand, what would the harm be if there is a ring in the bearing?

What grit of paper would you suggest for this polishing of shaft? The lapping compound is a powder that is mixed with oil to lap pistons to cylinders. It works very well.

Where does the .0006 come from? Is the new shaft .4375 in the rear?

The problem I see is taht you are going to have to try to take off .003 at least, preferably more, off a steel (and possibly hardened) shaft. That's a little beyond just polishing it lightly with sandpaper. .0006 (or .0001) of "bulge" is moot in comparison. It can be done but will have to be very aggressive.

Brett

RandySmith · « **Reply #5 on:** February 23, 2019, 10:23:06 PM »

Quote from: frank mccune on February 23, 2019, 06:06:40 PM

Hello Dan and Randy:

Thanks for the prompt and informative replies.

I measured the two shafts and found that they are different in diameter. When measured on the end where the threads begin the new one measured .4380" and right in front of the intake port it measured .4381". The original shaft measured .4375" at both places. I interpret this to indicate the shaft has a bulge of .0006" in front of the intake port. I did insert the shafts into the case from both ends to determine where the problem may lie as Randy suggested.

I guess that the best method to remove the bulge is to place the shaft in a chuck and apply some fine paper and oil. However, I doubt that I have a chuck that will hold the shaft true enough for this process to be accurate. Perhaps a light lapping to the case may solve the problem, but I will be using the bulge to lap a "ring" in the crankshaft bearing at the tight spot. On the other hand, what would the harm be if there is a ring in the bearing?

What grit of paper would you suggest for this polishing of shaft? The lapping compound is a powder that is mixed with oil to lap pistons to cylinders. It works very well.

Be well friends,

Frank McCune

Hi Frank
Tough job, and not really something you should try, You should either ream the bushing out to fit, .003 to .004 thou larger, or find someone with a tool post grinder on their lathe that can grind the crank, They sell an adjustable reamer, that is not real expensive that you could use to open the case out to fit the crank

Randy

Brett Buck · « **Reply #6 on:** February 24, 2019, 12:30:05 PM »

Quote from: RandySmith on February 23, 2019, 10:23:06 PM

Hi Frank
Tough job, and not really something you should try, You should either ream the bushing out to fit, .003 to .004 thou larger, or find someone with a tool post grinder on their lathe that can grind the crank, They sell an adjustable reamer, that is not real expensive that you could use to open the case out to fit the crank

Randy

And it would definitely have to be a grinder, there's no way that you would be able to get .003 off of it by cutting with regular tool. I wold think that would be bare minimum clearance.

The reamer sounds like a much better idea, and much easier to control the results than trying to use sandpaper (or as might be tempting, a *file*).

Brett

Air Ministry . · « **Reply #7 on:** February 24, 2019, 08:24:08 PM »

https://www.amazon.com/4380-11-125mm-Straight-Chucking-Reamer/dp/B07DWJ81C1

Cor, gee wilikers . they want 15 bucks .

Was going to suggest skinflint method , wheras if a drill bit ( metric ) was within a gnats dick of korekt ,
it'd open it out . To far if you didnt get it wright .

As your 4380 = 11.1252 mm , a 11 mm drillbit , if you got out of the right side of bed etc
should get it spot on . Seeing a 7.65 drill threw a OS alumn. intake gave .290 , using a drill press . Which is about what I wanted !

Id use a Tap Handle ( Tap & die type ) on the drill bit . It'd want to feed in easy , or youd be stuffed .
The Reamer would be the decadent option , and presumeably failsafe .

Just thow your .4380 in. on google search , to find them by the million .

Air Ministry . · « **Reply #8 on:** February 24, 2019, 09:16:27 PM »

A good used run in bit would be preferable to new

bob whitney · « **Reply #9 on:** February 24, 2019, 09:34:36 PM »

I have a .437 crank u are welcome to

Brett Buck · « **Reply #10 on:** February 24, 2019, 09:49:39 PM »

Quote from: RandySmith on February 23, 2019, 10:23:06 PM

Hi Frank
Tough job, and not really something you should try, You should either ream the bushing out to fit, .003 to .004 thou larger, or find someone with a tool post grinder on their lathe that can grind the crank, They sell an adjustable reamer, that is not real expensive that you could use to open the case out to fit the crank

Fixed, but oversize (by about the right amount to get it started) - https://www.mcmaster.com/3087a36 $30

Brett

Author Topic: McCoy .35 RH crankshaft-case bearing clearence fit????? (Read 1101 times)

frank mccune

McCoy .35 RH crankshaft-case bearing clearence fit?????

Dan McEntee

Re: McCoy .35 RH crankshaft-case bearing clearence fit?????

RandySmith

Re: McCoy .35 RH crankshaft-case bearing clearence fit?????

frank mccune

Re: McCoy .35 RH crankshaft-case bearing clearence fit?????

Brett Buck

Re: McCoy .35 RH crankshaft-case bearing clearence fit?????

RandySmith

Re: McCoy .35 RH crankshaft-case bearing clearence fit?????

Brett Buck

Re: McCoy .35 RH crankshaft-case bearing clearence fit?????

Air Ministry .

Re: McCoy .35 RH crankshaft-case bearing clearence fit?????

Air Ministry .

Re: McCoy .35 RH crankshaft-case bearing clearence fit?????

bob whitney

Re: McCoy .35 RH crankshaft-case bearing clearence fit?????

Brett Buck

Re: McCoy .35 RH crankshaft-case bearing clearence fit?????