Gotta crankpin question.

[Z.hb71]

Sooooooo I'm having a hard time finding a rod with a 14mm pin, most have 16 or 18mm so my question is, can I lathe down the ends that go into the crank down to 14mm but the center is still 16 or 18 ? Bassically make it look like this. Will this have any bad effects ?
This is for the 70cc build BTW

 

[crucialRC]

I think it would depend on the thickness of the rod. No matter what, taking another 2mm of material away will weaken it from its original engineered purpose. The question would be if the removed material and horsepower/torque of the engine will not be enough for detrimental damage.

 

[Seandonato73]

The real question will be if it's been hardened and if so how deep the the harness goes. And what type of material that is made of. It may be easier to get a new bar made. Imo tool steel would hold up well. We used to make custom wrist pins at the machine shop for a guy that tractor pulled out of tool steel. It held up very well. This is something a competent crank machinist should be able to make up for you.

 

[Z.hb71]

The real question will be if it's been hardened and if so how deep the the harness goes. And what type of material that is made of. It may be easier to get a new bar made. Imo tool steel would hold up well. We used to make custom wrist pins at the machine shop for a guy that tractor pulled out of tool steel. It held up very well. This is something a competent crank machinist should be able to make up for you.

So I should get a pin made VS modding the pin the rod comes with ? Really would love to get a custom rod made but that's probably gunna b really expensive and time consuming. Maye b I will get a custom made but who knows. Also isn't titanium stronger than tool steal ? If so why not make one outa titanium ?

 

[Seandonato73]

I'd just get a new crank pin made up that's fits your rod. Tool steel should be plenty strong. We didn't use titanium much so I cant say. I know it's very difficult to machine and I recall something about smearing. But like I said we didn't use it much.

 

[Z.hb71]

I'd just get a new crank pin made up that's fits your rod. Tool steel should be plenty strong. We didn't use titanium much so I cant say. I know it's very difficult to machine and I recall something about smearing. But like I said we didn't use it much.

Kay I guess that's what I'll do ? I'll try to find more info on titanium, if it's a PITA I'll go tool steel. Thx fir the info, u saved the day once again lol
EDIT: I'll probably end up using steel cuz I've read that Titanium sucks for a sliding surface and will wear fast which is not ideal ? for a crankpin so probably will use steel afterall ?

 

[crucialRC]

Z, why not go and talk to a machine shop and tell them your plans? A good machinist will give you good info on what he would do. Machine shops are built off reputation and word of mouth. I have one near me that I use for all my full scale engine builds and he's straight up with me and I take his suggestions.

 

[Z.hb71]

Z, why not go and talk to a machine shop and tell them your plans? A good machinist will give you good info on what he would do. Machine shops are built off reputation and word of mouth. I have one near me that I use for all my full scale engine builds and he's straight up with me and I take his suggestions.

Well I'm not sure if there's any good machine shops/engine building shops near me but if there is I'll definitely do that ?
EDIT: there's a bunch of shops near me but I need to know if they can do anything for me so I'll email them once I'm ready ? or I could see if the guy who I get the crank rebuilded by can do it, either way, ill make it happen ?

 

[crucialRC]

Can you Google the shops near by to see any reviews? Or possible go to a drag strip or cruise night and ask the guys where they get work done. I know my machinist wouldn't answer an email quickly. He's an older gentleman and technology isn't his thing but he can build a bulletproof engine block. Might be easier to go talk to them and gauge their knowledge.

 

[Top Dead Center]

You could have a rod journal machined out of 4340 steel. Spec sheet for 13mm. If I was building this, I would stay with the 14mm crank pin and buy the rod with 18mm large end and use needle roller bearings to make up the difference.
https://www.ntnglobal.com/en/products/catalog/pdf/2300E_03.pdf

 

[Z.hb71]

Can you Google the shops near by to see any reviews? Or possible go to a drag strip or cruise night and ask the guys where they get work done. I know my machinist wouldn't answer an email quickly. He's an older gentleman and technology isn't his thing but he can build a bulletproof engine block. Might be easier to go talk to them and gauge their knowledge.

Yeah most of them have 4-5 stars which is great but still don't know if they can do 2 stroke stuff, probably can. No cruise nights or drag nights happen here unfortunately. ?

You could have a rod journal machined out of 4340 steel. Spec sheet for 13mm. If I was building this, I would stay with the 14mm crank pin and buy the rod with 18mm large end and use needle roller bearings to make up the difference.
https://www.ntnglobal.com/en/products/catalog/pdf/2300E_03.pdf

I could do that also.

 

[1Coopgt]

Sooooooo I'm having a hard time finding a rod with a 14mm pin, most have 16 or 18mm so my question is, can I lathe down the ends that go into the crank down to 14mm but the center is still 16 or 18 ? Bassically make it look like this. Will this have any bad effects ? View attachment 48341
This is for the 70cc build BTW

So what is the bearing thickness ? You didn't mention it that I noticed. Ya got to have bearings between the rod and crank . I'm guessing the Crank web area rides in ball bearings . Normally the rod rides on some type of brass bearing ,guessing 2 piece that comes in from the sides .

 

[Z.hb71]

So what is the bearing thickness ? You didn't mention it that I noticed. Ya got to have bearings between the rod and crank . I'm guessing the Crank web area rides in ball bearings .

It rides on roller needle bearings, what do u mean by bearing thickness? Like the wall of it? If so probably somewhere near 2mm but I haven't decided on the rod exactly

 

[1Coopgt]

Well you kind of need to decide all that . The inside dia of the bearing needs to be pretty tight to the crank od . The the od of the bearing needs to fit the ID of the crank rod end .

So your crank journal is 14mm ? the bearing id/od's going to take up the space between the crank and rod . If the bearing is 2MM then I'd guess you need a rod with 16mm ID. Pretty simple but you need to work with the tolerances. To loose and you'll destroy the crank and possible the rod too.

when you decided to build your own engine you bit off a really big chunk . Tons of research to be done . You should be in constant contact with the folks you bought that engine from. They should be able to tell you every thing you need to build it . If not .....

 

[Z.hb71]

Well you kind of need to decide all that . The inside dia of the bearing needs to be pretty tight to the crank od . The the od of the bearing needs to fit the ID of the crank rod end .

So your crank journal is 14mm ? the bearing id/od's going to take up the space between the crank and rod . If the bearing is 2MM then I'd guess you need a rod with 16mm ID. Pretty simple but you need to work with the tolerances. To loose and you'll destroy the crank and possible the rod too.

Yup I'm figuring that out, btw yes my crank journal is 14mm, I need a rod with 13-13.50m width and prefferably a 16 mm pin and 100-105mm length. So basically what your saying is don't mess with the pin (like mod or make a new one) and just make up the difference with a 16-18mm od bearing to fit the 16-18mm Id of the rod with a 14mm Id on the bearing correct ? Hope that made any sort of sense.

when you decided to build your own engine you bit off a really big chunk . Tons of research to be done . You should be in constant contact with the folks you bought that engine from. They should be able to tell you every thing you need to build it . If not .....

Yeah well, I doubt ALX would help me build there own engine. Nor do they like to respond to emails. RCMAX helped me a bit, tho they didn't know much about ALX cuz it's not their engine obviously, also sum owners helped me abit. I had to pretty much design it by myself but once it's said and done thats another throphy in my opinion

 

[1Coopgt]

Why aren't you sourcing the parts (rod, bearings, wrist pin and I'm guessing the piston) from the folks that sold you the engine ? They should have everything you need . I can't tell you what you need . I do know what i'm talking about but even I only have a general understanding of how it should be put together . Last time I worked on an engine it was a Dodge 340ci and even then I didn't dig into the internals . I let my buddy do that it was his car . Last thing I would want to do is mess up someone else's engine ,

 

[TODD]

Make your ouwn out of tool steel . Not hard to do and than harden it. We did a lot of this in our first engines. The other thing you can do if the crank wheel has enough wall thickness on the wheels from the edge of the crank pin hole? Is bore it bigger to the 16mm size. Just keep in mind you need a good press fit and wall thickness so it does not bulge out and take away the press fit.

 

[Z.hb71]

Why aren't you sourcing the parts (rod, bearings, wrist pin and I'm guessing the piston) from the folks that sold you the engine ? They should have everything you need . I can't tell you what you need . I do know what i'm talking about but even I only have a general understanding of how it should be put together . Last time I worked on an engine it was a Dodge 340ci and even then I didn't dig into the internals . I let my buddy do that it was his car . Last thing I would want to do is mess up someone else's engine ,

The Piston is the same as they use, I think ALX has a custom rod which they will probably over charge and it's all the way in Italy, theyre probably not willing to share they're secrets but even if I tried they won't respond!!

Make your ouwn out of tool steel . Not hard to do and than harden it. We did a lot of this in our first engines. The other thing you can do if the crank wheel has enough wall thickness on the wheels from the edge of the crank pin hole? Is bore it bigger to the 16mm size. Just keep in mind you need a good press fit and wall thickness so it does not bulge out and take away the press fit.

Can't drill the crank cuz Ive got to remove meterial from
The inside of the crank so if I drill it, it will be really weak. I personally can't make a rod myself cuz I'm not experienced and don't have the resources. I prefer to buy a rod but if it comes to it, I'll splurge and get me made a billet aluminum rod

Make your ouwn out of tool steel . Not hard to do and than harden it. We did a lot of this in our first engines. The other thing you can do if the crank wheel has enough wall thickness on the wheels from the edge of the crank pin hole? Is bore it bigger to the 16mm size. Just keep in mind you need a good press fit and wall thickness so it does not bulge out and take away the press fit.

Can't drill the crank cuz Ive got to remove meterial from
The inside of the crank so if I drill it, it will be really weak. I personally can't make a rod myself cuz I'm not experienced and don't have the resources. I prefer to buy a rod but if it comes to it, I'll splurge and get me made a billet aluminum rod

 

[1Coopgt]

The Piston is the same as they use, I think ALX has a custom rod which they will probably over charge and it's all the way in Italy, theyre probably not willing to share they're secrets but even if I tried they won't respond!!

Sorry to hear that . The last thing I wan't to do is tell you the wrong info. I don't want to be the one that gives you bad info that messes up your engine .

 

[Z.hb71]

Sorry to hear that . The last thing I wan't to do is tell you the wrong info. I don't want to be the one that gives you bad info that messes up your engine .

Yup, I understand ?