7mm

[blowit]

You can hold the webs in a set of prismatic vice jaws and support it with a set of parallels. Pressing the crank together shouldn't need a special fixture if you take your time doing it and measure the distance between the thrust pads on the webs as you go.

 

Your problem is going to be that once you have machined the first web, you will have dial indicate in all of the subsequent parts. There are many ways to do this, but the least difficult methods are also the least accurate (example: a coaxial dial indicator is only good for +/-.001" no matter what its rated for). Now you could make a fixture with a center and a dowl pin on it to take any positional variance acroos the four parts out of the equation, but that requires adding a small manufacturing feature to all of the webs and you may wind up being just as accurate doing that as you were if you dialed each part in individually. Either way it's alot of work. The forgings are a mixed blessing because of all this in this particular application.

 

It actually takes alot less time if you are making small quantities of thi type of crankshaft to make the webs from billet. If you have access to a CNC mill, it also winds up being cheaper to do if you convert hours spent working to dollars. :geek:

 

 

I really figured that someone would have chimed in that you need an ID grinder to do this correctly. We build our own stroker cranks and the true position of those journal bores must be tight!! .0005 unless you want it to vibrate apart and want it to true in at all. Truing the crank is one thing, locating the journals, not easy and we have jigs to do it. We even buy the cranks at times.

 

I would say it can be done several ways as long as severe amounts of time are taken to ensure accuracy. The bore head may work but they have big issues with the spring passes in steel and making them repeat to the tight tolerance needed may not work so well. They can remove .0005 by accident. Typical bore heads are graduated to .001 offset meaning .002 in the diameter. Trying to hold .0005 in steel, all the way through the bore, CNC is a minimum because feeds/speeds must maintain constant to repeat the cycle for the next web if you get it right.

 

My only advice, if someone dives in, consider boring the holes to -.001 and have them ID ground to spec. You would need to take the pins for verification because you never go that precise and not consider temperature and type of measuring tool used. Their methods will be much better for an accurate fit.

 

Now why does this have to be so perfect since you are welding it? Well, the crank web was never engineered for a +10mm or even +14mm. These forces can actually take a welded crank apart. Rod speed is way up there thus reducing engine life by about 60% anyway. By holding tight interference fits, you can reduce the chance of a crank breaking the welds and separating. Hope that helps. I am not trying to detour, only inform on this. It is tricky, this the reason most mom and pop shops don't do there own crank stroking. Now THAT just sounds perverse.

 

B

[FireHead]

I really figured that someone would have chimed in that you need an ID grinder to do this correctly. We build our own stroker cranks and the true position of those journal bores must be tight!! .0005 unless you want it to vibrate apart and want it to true in at all. Truing the crank is one thing, locating the journals, not easy and we have jigs to do it. We even buy the cranks at times.

 

I would say it can be done several ways as long as severe amounts of time are taken to ensure accuracy. The bore head may work but they have big issues with the spring passes in steel and making them repeat to the tight tolerance needed may not work so well. They can remove .0005 by accident. Typical bore heads are graduated to .001 offset meaning .002 in the diameter. Trying to hold .0005 in steel, all the way through the bore, CNC is a minimum because feeds/speeds must maintain constant to repeat the cycle for the next web if you get it right.

 

My only advice, if someone dives in, consider boring the holes to -.001 and have them ID ground to spec. You would need to take the pins for verification because you never go that precise and not consider temperature and type of measuring tool used. Their methods will be much better for an accurate fit.

 

Now why does this have to be so perfect since you are welding it? Well, the crank web was never engineered for a +10mm or even +14mm. These forces can actually take a welded crank apart. Rod speed is way up there thus reducing engine life by about 60% anyway. By holding tight interference fits, you can reduce the chance of a crank breaking the welds and separating. Hope that helps. I am not trying to detour, only inform on this. It is tricky, this the reason most mom and pop shops don't do there own crank stroking. Now THAT just sounds perverse.

 

B

 

The ID grinding is what I was getting at with my jig grinding statement in my previous post. 10 microns true position is usually what I will wind up with for a tolerance if I am recreationally making a Banshee crank. I could probably do better, but I'm lazy.

 

I disagree that a CNC mill is 100% necessary to get this project done, but it does give you a much better chance of creating a good crankshaft. Furthermore, if what you say is true about your boring heads, you need to buy a better boring head(s). My Sandvik heads repeat to 1 micron. As you point out a constant 20 degree celsius is a must for accurate machining of steel like we are talking about, as well as control of humidity and temperature.

 

As you say, welding the crank is only done to preserve the press fit. There seem to be a current of folks on the HQ that like to disagree with me on this. For what reason I have no idea, but they usually cite a source such as some undisclosed big name builder told them so or they heard it from their sister's(actually mother) boyfriend (actually brother).

[blowit]

The ID grinding is what I was getting at with my jig grinding statement in my previous post. 10 microns true position is usually what I will wind up with for a tolerance if I am recreationally making a Banshee crank. I could probably do better, but I'm lazy.

 

I disagree that a CNC mill is 100% necessary to get this project done, but it does give you a much better chance of creating a good crankshaft. Furthermore, if what you say is true about your boring heads, you need to buy a better boring head(s). My Sandvik heads repeat to 1 micron. As you point out a constant 20 degree celsius is a must for accurate machining of steel like we are talking about, as well as control of humidity and temperature.

 

As you say, welding the crank is only done to preserve the press fit. There seem to be a current of folks on the HQ that like to disagree with me on this. For what reason I have no idea, but they usually cite a source such as some undisclosed big name builder told them so or they heard it from their sister's(actually mother) boyfriend (actually brother).

 

 

 

There again Firehead, I was generalizing in that "most" boring heads will indicate at .001. So just how much did you pay for that boring head? As much as it would cost to buy a crank or close to. We have them and rarely use them. TOO slow. we both know, a new tool holder, precision head, carbide bar, are all a must to repeat a hole but we know better than to mess around with a bore head because a grinder can just do it much faster and more accurate. Now I am not tryin to be rude at all but more or less curious as to your profession in which you can or need to actually hold a 1 micron tolerance with a bore head?

 

It is one thing to make a hole within 1 micron but another to do it in a repeatable fashion. One small chip in the tool holder during ATC, and you now have substantial runout in the bore head which will make a nice, oversized hole. I guess all I am saying is 1 micron is tough stuff, period.

[FireHead]

There again Firehead, I was generalizing in that "most" boring heads will indicate at .001. So just how much did you pay for that boring head? As much as it would cost to buy a crank or close to. We have them and rarely use them. TOO slow. we both know, a new tool holder, precision head, carbide bar, are all a must to repeat a hole but we know better than to mess around with a bore head because a grinder can just do it much faster and more accurate. Now I am not tryin to be rude at all but more or less curious as to your profession in which you can or need to actually hold a 1 micron tolerance with a bore head?

 

It is one thing to make a hole within 1 micron but another to do it in a repeatable fashion. One small chip in the tool holder during ATC, and you now have substantial runout in the bore head which will make a nice, oversized hole. I guess all I am saying is 1 micron is tough stuff, period.

 

Just so we're on the same page, I know you were being general and I was just flipping you shit. :thumbsup:

 

The particular Sandvik head that I was speaking of cost around $4500 for the head and another $1000 for the HSK63A back end. I should also clarify that the bar belongs to my company and not me. Of course that is just for a bar that has a 10mm dia. range of adjustment that covers the size of a Banshee pin dia. When I bought that particular boring set up I also purchase heads an back ends to cover a bore from 5mm dia. to 6" in dia. in various depths and increments. Including inserts and such I think the P.O. I signed was about $100k.

 

1 micron true position is easily reapeatable witha good mill, probe, tooling, fixture, and operator. The secret (not really a secret) to our success with holes of this tolerance is in our probing routines. Even with a hole bored to that tolerance, you probably still need to jig grind the hole to get a good surface finish, to facilitate the best press fit, and eliminate any taper. Like you said, 1 micron is tough stuff, even if you grind the bored hole.

 

If you look in my signature you might be able to guess what I do for a living or atleast who I work for. :thumbsup:

[dajogejr]

If you look in my signature you might be able to guess what I do for a living or atleast who I work for. :thumbsup:

 

You guys totally lost me at Sadnvik....

 

If you look even closer, you will see the company firehead works for spelled backwards on the valve cover...

[FireHead]

You guys totally lost me at Sadnvik....

 

If you look even closer, you will see the company firehead works for spelled backwards on the valve cover...

 

The backwards spelling is the unfotunate side effect of making the my signature look better (mirriored that engine). Dinner made it for me. I kinda like it. :smile:

 

If there is any interest for those who don't know what or who Sandvik is: www.sandvik.com

[Toybreaker]

Yeah i have a good bridgeport a full set of carbide boring bars and a decent boring head. adjusts in .0001 increments. I am confident in holding .0005 true position with my tooling and equipment

[FireHead]

Yeah i have a good bridgeport a full set of carbide boring bars and a decent boring head. adjusts in .0001 increments. I am confident in holding .0005 true position with my tooling and equipment

 

I don't know how you are going to hold .0005" across all four webs, but I learn something new every day. I just realized you were in San Diego, if you need help or get in a bind with this project, give me a shout.

 

There is a guy in our engine shop that can group piston by weight just by picking them up. Most the time he is right within a tenth of a gram. Our QC dept. are the folks that actually do the component matching, but the weighing by hand thing is a damn cool bar trick. I am not sure why I just told that story.............it's not really the same thing as holding a tolerance on a true position dimension. :shoothead:

[Toybreaker]

That is a totally cool skill to have though. I have the demon tweak with holley (4150 4160) and quadrajet carbs. Just need to learn the demon tweak for the banshee carbs, I am getting there. When i start this project i will be in the indian ocean or northern arabian gulf.

I am going nowhere off the ship for 3 months at least so if it takes me a month to get everything "perfect" before I get a bead laid down that is fine by me. :biggrin:

[Toybreaker]

ok now i have a clear understanding that i should just save the money from drinking in one port and buy the crank. But i still need to trench the cases. Any info on that?

[FireHead]

ok now i have a clear understanding that i should just save the money from drinking in one port and buy the crank. But i still need to trench the cases. Any info on that?

 

If I were you, I would save the beer money and buy a crankshaft from someone like Twister. To add a bit of scale to this discussion, you don't see me offering to do the machine work for you, which I would do if it were an easy task.

 

You will need to have your cases trenched /clearanced / machined (take you pick of terms) inorder to run anything larger than 4mm additional stroke. What sort of info are you looking for in regards to this?

 

I hate to ask an off topic question, but what was the Demon tweak you were talking about in regards to Holley carbs? I apologize if it's a dumb question. I am not much of a car guy. :geek:

[Toybreaker]

Provided the carb is in good repair (doesn't leak air around the throttle shafts) I can usually make it run better with just a few minor adjusments.

Provided the jetting, secondaries open when they should(holley 4160 and quadrajet), accelerator pump squirters and cam are correct. If they aren't i can tune those in too.

2 strokes are a completely different animal. different learning curve all together.

 

As far as what is needed for trenching/clearancing. do you line bore the cases or lay it out and grind the clearance?

Edited March 16, 2007 by Toybreaker

[FireHead]

Provided the carb is in good repair (doesn't leak air around the throttle shafts) I can usually make it run better with just a few minor adjusments.

Provided the jetting, secondaries open when they should, accelerator pump squirters and cam are correct. If they aren't i can tune those in too.

2 strokes are a completely different animal. different learning curve all together.

 

As far as what is needed for trenching/clearancing. do you line bore the cases or lay it out and grind the clearance?

 

I guess I am a little in the dark about what is actually modified on the Holley carbs. I know Demon had fotten into some patent issues with Holley awhile back. You can get as technical as you want. I was trying to make a joke when I said I wasn't much of a car guy. :ohmy:

 

Whit regard to the case trenching (which is a silly term, but that is what folks use around here), there are several ways to do it. Most people use a die grinder with a carbide rotary burr or a cyclinder head porting tool (originally made for the jewelry industry) that is commonly made by Fordom (Foredom?) with a similair carbide burr to what you might put in a die grinder. Ipersonally use a 5-axis CNC mill, but I am an extreme exception. You can also get away with doingit on a 3-axis, CNC, vertical mill if you do the programing with CAM package.

 

You should never have to line bore the cases unless you are fooling with the bearing pockets, which ypu shouldn't be if you're just trenching the cases for a stroker crankshaft. The trick wind up being that you generally have to remove enough material for a +10mm cranks that you break through the top case half behind the cylinder mounting surface. You then have to add material by welding (usually before you break through) or with epoxy. :thumbsup:

[Toybreaker]

my prefered term would be clearancing but it seems that most people on the board refer to it as trenching.

I have a foredom deburr motor and a full set of rasps and burrs. So if i take this project on i will do it that way.

I am not going to do any weld build up so 10mm is out. need it for 7mm?

[FireHead]

my prefered term would be clearancing but it seems that most people on the board refer to it as trenching.

I have a foredom deburr motor and a full set of rasps and burrs. So if i take this project on i will do it that way.

I am not going to do any weld build up so 10mm is out. need it for 7mm?

 

You have to do the same amount of clearancing for 7mm and 10mm stroker crankshafts. The is because the 7mm and 10mm crankshafts are generally made from the same web forging.

 

If you buy a billet web crankshaft then you may not have to clearance the cases for a 7mm crank as much as for a 10mm crank. I don't know that for sure though, maybe someone else can verify that.