Crankshaft tap

SIMPLEARKANSAN

SIMPLEARKANSAN

New Member
#1
#1
I have a great running tec 3.5 hp with at 5/8" crankshaft. I want to tap it to fit a 1/4" bolt to hold on my clutch. I bought a tap and die set from Lowe's. My question is to tap to fit a 1/4" bolt, do I use a 1/4" drill bit followed by a 1/4" tap? I know it sounds so basic, but I only want to do this once.:rolleyes:
 
Sixpac440

Sixpac440

#3
#3
Tapping advice:
Unless you have a reversible drill press and experience tapping it is best to hand tap.
Keep the tap well lubed and clean. If it offers too much resistance back it out, clean it, re-lube it, blow out the hole and tap some more.
Smaller taps are fairly easy to snap so keep even pressure on the handle when turning.

I would tap it 5/16-18 and use a 17/64 drill ....
Chamfering your hole after drilling will help guide the tap, give the bolt a guide when starting and keep the metal from puckering from the tap displacing metal when it starts.
 
ATKRIDER

ATKRIDER

New Member
#4
#4
I agree with Sixpac. I know for sure this can go bad real quick. Crankshafts are pretty tough. Personally I go with fine thread so the tap isn't taking too big of a "bite". Also the only want to do it once quote is probably better defined as you only have one shot at this. I suggest getting Cobalt drill bits and a super premium tap like a Greenlee or something US made. Just advice from someone that has done this.
 
Sixpac440

Sixpac440

#5
#5
I agree with ATKRIDER good drills and taps for cutting new holes are a good idea. Also fine thread will make the job a little less "risky" in terms of tap breaking.
 
K

kensmachine

New Member
#6
#6
If the taps are not HIGH SPEED STEEL don't use them to cut new threads I don't like carbon steel taps tip if the tap docent have HS or HIGH SPEED on it its mostly likely a carbon steel tap Ken
 
ole4

ole4

#7
#7
Three tips if you have never done this before.
1) Use a thread cutting lube
2) make sure tap is going into the hole straight. best to chuck in a lathe and put tap in the tailstock chuck.
3) Every few turns, back the tap out (counterclockwise/anticlockwise) to clear away chips of loose material. This is especially important in a blind hole, one that does not go all the way through the work piece like a crankshaft.
 
ATKRIDER

ATKRIDER

New Member
#9
#9
All I will say is there is a HUGE difference in tools such as this. For tapping some NC threads in a piece of 1/4" mild steel it is probably all good but what you are going to attempt honestly should be left to a competent machine shop BUT since we all like the feeling of achievement when we do things of this nature I really suggest kicking it up a few notches. A single quality tap for cast from say McMaster in 5/16 nf will run you about $35. And a Cobalt drill bit around $12. With shipping that's over 50 bucks.

If you start to drill the hole and the drill bit you have breaks-now what? Probably be looking for a crank for $75-$100. Than again maybe you are one of those people that just have real good luck with these things. I am NOT one of those people. Tapping a crankshaft is a tough nut even with the best tools. Again maybe some get lucky and it is easy as pie but for me-NEVER.

Just a thought-maybe the clutch has a couple of set screws running at 90degrees to the shaft length so you really don't need to mess with tapping it. That is probably wishful thinking but might solve this real easy. Seems like most clutches now a days all have set screws-that would allow you to just avoid this all together.

I am NOT trying to be all negative about this-just trying to save you from turning a good running engine into a possible door stop-:thumbsup:
 
KustomKartKid

KustomKartKid

Administrator
#11
#11
I don't think I own a 4 stroke minibike with a crank bolt...just set screws. You could leave the set screws out and it wouldn't fly off unless the chain broke.
 
we4amigos

we4amigos

Member
#13
#13
You'll be glad you did. Socket Set Screws exert a tremendous amount of pressure in a very small area. They are all made from alloy steel with tensile strengths around 180,000. Manufactures actually recommend tightening till the hex key (Allen wrench to some) breaks off flush. If your clutch has two,fat chance it would ever come off.
Best of luck
 
Sixpac440

Sixpac440

#14
#14
I'm kinda sad to see you were scared off of trying to tap the crank.
Sounds like if it all went south you could still use the set screws.
I'm a die maker and have tapped a lot of holes including at least 2 cranks.
The cranks are cast steel and when tapping feel like tapping cast iron which taps fairly easily.
The only way you learn to tap like most anything is to just jump in and do it!
I think with the sage advice offered here your first foray into tapping will be a success!
Take this from a guy who has broken a lot of taps!
So don't return the kit, drill/tap and take pics and post your experience!
 
H

Havasu Dave

Moderator
#15
#15
Max Torque no longer agrees:

"The standard clutch is no longer drilled and tapped for set screws because they are not needed. You never fix both sprockets in a locked position. Only the axle sprocket needs to be in a fixed position. A clutch must be able to float on the crankshaft so it can self align."
 
CarPlayLB

CarPlayLB

Well-Known Member
#16
#16
I use Hilliard clutches as they have the cheapest ($45) that can be adjusted. They include a crank bolt with their kit. I guess it depends upon whose clutch you are using Hilliard's Extreme Duty - 3/4" 12 Tooth #35 Clutch
I drill and tap my own. Have limited skills, and not the brightest bulb, but I do find it a very simple procedure. I cheated and bought the fixture that OMBW used to sell. It is the collar that goes over the crank and allows you to drill it straight. I don't think I would try it without it, but with the tool it is a snap!
 
H

Havasu Dave

Moderator
#17
#17
Sixpac440 said:
I'm kinda sad to see you were scared off of trying to tap the crank.
Sounds like if it all went south you could still use the set screws.
I'm a die maker and have tapped a lot of holes including at least 2 cranks.
The cranks are cast steel and when tapping feel like tapping cast iron which taps fairly easily.
The only way you learn to tap like most anything is to just jump in and do it!
I think with the sage advice offered here your first foray into tapping will be a success!
Take this from a guy who has broken a lot of taps!
So don't return the kit, drill/tap and take pics and post your experience!
Click to expand...
100% agree with this. I haven't seen a crank yet that didn't have a gear puller detent in the end, which makes a great guide for drilling. This is an easy one to tap. (I do now own some tap removal tools, since I have broke taps on other things)

I end up running a tap through everything I get that is old, especially tapped holes in aluminum wheels that have experienced galling. You probably have some great machining skills being a die maker!
 
SIMPLEARKANSAN

SIMPLEARKANSAN

New Member
#18
#18
Thanks for the input. I've already taken the tap and die set back to Lowe's. Took the money and bought a craftsman multi level rolling tool chest that a friend wanted to let go for real cheap. I may later decide to tackle the crankshaft project as you've all given great information and encouragement.
 
I

izzyizz

New Member
#19
#19
Tapping a crank is cake drill 17/64 hole about 3/4 deep using.oil an.keep the drill straight an.level adding oil.ad needed then tap 5/16 fine thread agian use the oilan dont spply to.much pressure an keep straight an level tsp a little back out oil keep going till reach end take out clean hole oil.an put bolt in....
 
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