Scottydog Posted December 17, 2012 Report Share Posted December 17, 2012 Here's a question for some machinist / engineers out there! So I've got a full circle crankshaft which I need to add an extra 8mm to the total diameter to make it useful for my project. I was thinking if I had 2, 4mm thick rings made with an interference fit I could shrink fit them in place. Are there any considerations I should make in the process? Will the rings stay in place or would small evenly spaced TIG welds be worth considering? I was thinking I should be able to put them on without disassembling the crankshaft. The other option is to make aluminum rings and loctite into the casings, but the inertia might be lacking some. On the inertia front, are there any rules or calculations in that regard. cheers for your thoughts! Link to comment Share on other sites More sharing options...
porter_jamie Posted December 17, 2012 Report Share Posted December 17, 2012 Is it a stroker? Will the piston still clear? You trying to reduce ccase volume I guess. Anything is possible, but what are you trying to achieve? Link to comment Share on other sites More sharing options...
speedy sie Posted December 17, 2012 Report Share Posted December 17, 2012 yep crank case packing seen this done before in some of the nsa sprint bikes engines. Link to comment Share on other sites More sharing options...
Scottydog Posted December 18, 2012 Author Report Share Posted December 18, 2012 Hey thanks guys. Just looking to fit a superior crankshaft which comes with a smaller diameter. There is no high performance option to drop straight in so next best option is using a smaller diameter race crank and add the extra diameter needed to bring dimensions back to standard. Link to comment Share on other sites More sharing options...
blur1 Posted December 18, 2012 Report Share Posted December 18, 2012 Is there no option for a bigger one you could machine down? Always preferable to 'adding' material. Link to comment Share on other sites More sharing options...
Scottydog Posted December 18, 2012 Author Report Share Posted December 18, 2012 Only choice is to add unfortunately. Chatting to the machinist at work, he thinks should be no issue and would stay in place without any welds, as the rings would expand alot being largish diameter. I want to get some additional input and advice from those also experienced in similar work. Link to comment Share on other sites More sharing options...
Romski Posted December 18, 2012 Report Share Posted December 18, 2012 I would also check if there is any hardening on the crank. Link to comment Share on other sites More sharing options...
Scottydog Posted December 18, 2012 Author Report Share Posted December 18, 2012 I would also check if there is any hardening on the crank. Why is that, is there any concerns for the ring securing to it? There is no plan to machine it at all. Idea is to not need any machining on the circumference after. There might be a slight growth on the ring after being fitted. Link to comment Share on other sites More sharing options...
Gregorious77 Posted December 18, 2012 Report Share Posted December 18, 2012 moment of inertia pg4 http://www.freestudy.co.uk/engineering%20science%20h1/outcome%202%20%20t1.pdf other stuff http://www.freestudy.co.uk/mechprinc+2007/3t1.pdf You best calculate the rings interferance at the worst case point i.e. fully warmed up and at full rev limit. There will be some large forces involved I would imagine. Link to comment Share on other sites More sharing options...
Scottydog Posted December 18, 2012 Author Report Share Posted December 18, 2012 Hey thanks for the links. I wanted to look into some of that as would be good to know what's at stake! I was thinking of how much would the crankwebs grow at full revs and how much would the ring grow, do they grow in unison? Both will be at same temp, so should grow thermally together. I'm sure there are many other applications with rings on wheels, trains for example. My gut feeling is it'll be fine, but still would be good to see for sure what theory says. Link to comment Share on other sites More sharing options...
Romski Posted December 18, 2012 Report Share Posted December 18, 2012 Why is that, is there any concerns for the ring securing to it? There is no plan to machine it at all. Idea is to not need any machining on the circumference after. There might be a slight growth on the ring after being fitted. If the ring is extending the circumference of the crank, then this might require hardening the same as the crank, if the crank is harden that is. Only wondering that's all really. Link to comment Share on other sites More sharing options...
krazyk Posted December 18, 2012 Report Share Posted December 18, 2012 What about stiffing the cases? Link to comment Share on other sites More sharing options...
Scottydog Posted December 18, 2012 Author Report Share Posted December 18, 2012 Stuffing is another option, could even partially cover like some race engines do. This was an idea originally, but with everyone going for high inertia cranks it might be a backwards method of tuning? I can still test this option out though as it's easier to do really. Link to comment Share on other sites More sharing options...
CRMotard Posted December 18, 2012 Report Share Posted December 18, 2012 If the crank ring is the way you want to go, it shouldn't move EVER as long as its a very tight fit once cooled down. but always remember that there is a big difference between adding weight and increasing inertia. why dont you just modify you current crank to be 'superior' Im assuming that your trying to install at TZ crank into an RGV or something like that? Link to comment Share on other sites More sharing options...
Ducsenna Posted December 18, 2012 Report Share Posted December 18, 2012 I had a crank refurbed, with material added, rather than replace it with a new one on my 748 RS . It ended in tears, mine, the shells seamed to spin on the crank and tear the added metal from the crank, like a peeled banana? I still have two old ones and am interested in how you get on! Link to comment Share on other sites More sharing options...
Scottydog Posted December 19, 2012 Author Report Share Posted December 19, 2012 If the crank ring is the way you want to go, it shouldn't move EVER as long as its a very tight fit once cooled down. I'm glad you say this. I was talking about the plan to a friend and we discussed. The thinking was hell if the press fit crank pin holds, then this should be fine. So the plan is to get the new crank and go with this method. The stock crank isn't really suited to be improved to be honest, so this is the best option. Wish me luck, I'll let you know how it goes next year. Link to comment Share on other sites More sharing options...
ronenige Posted December 19, 2012 Report Share Posted December 19, 2012 What bike is it ? Link to comment Share on other sites More sharing options...
Scottydog Posted December 19, 2012 Author Report Share Posted December 19, 2012 Derbi GPR moped. Link to comment Share on other sites More sharing options...
Scottydog Posted December 20, 2012 Author Report Share Posted December 20, 2012 So yeah basically the version I have runs a larger diameter crank and aftermarket wise no one makes racing items. When you look at the other version, must be at least 10 - 15 variations of full circle race ones with various degrees of increased stroke and rod lengths. So figured one way to upgrade is to slip rings on the outside an suddenly my choice gets pretty massive! Link to comment Share on other sites More sharing options...
Damnthistinleg Posted December 20, 2012 Report Share Posted December 20, 2012 Are none of these cranks any good? http://www.adrenalin-pedstop.co.uk/Products/List.aspx?page=4&CategoryID=4655 Does the Derbi use the Minarelli AM6? Link to comment Share on other sites More sharing options...
Scottydog Posted December 21, 2012 Author Report Share Posted December 21, 2012 Are none of these cranks any good? http://www.adrenalin...CategoryID=4655 Does the Derbi use the Minarelli AM6? Exactly those cranks are perfect, but I'll need to add to the diameter. They'll be 77mm dia, I need to bring them up to 83mm I think it is. All other dimensions will be fine. Link to comment Share on other sites More sharing options...
Damnthistinleg Posted December 21, 2012 Report Share Posted December 21, 2012 I can't remember which manufacturer of crank I bought to fit into my DT50 supermoto but yes, it made a surprisingly large difference to the power. I must rescue that little tiddler from the back garden and have a bit of fun with it! Link to comment Share on other sites More sharing options...
2T Institue Posted December 21, 2012 Report Share Posted December 21, 2012 Make a nylon stuffer for the cases you will find that's much easier. Link to comment Share on other sites More sharing options...
Scottydog Posted December 21, 2012 Author Report Share Posted December 21, 2012 Make a nylon stuffer for the cases you will find that's much easier. Nylon apposed to aluminium insert I mentioned earlier you're suggesting? We have a fair bit of that around the job, easier and cheaper than to bring in aluminium. Sounds like a good option, as I was looking at it but kinda dismissed it because it was plastic. Not sure if there are calculations or rules regarding ideal mass for a crankshaft, but if the unmodified crank is happy, or at least happy in a race setup then saves a bit of effort. For the street version, might still be worth running the extra mass. Plan to run a 53mm piston on a 94mm rod with a 44mm stroke. Seen some aftermarket setups running 55mm piston on a 46mm stroke on the smaller mass flywheel, so some designers felt it was okay. Link to comment Share on other sites More sharing options...
kaighn80 Posted March 8, 2013 Report Share Posted March 8, 2013 If this was a con rod the option would have been to have the caps machined down and then line bore the whole thing so that the con rods bolted up in a similar fashion to how the factory intended iyswim, could this not be done? Of course there would still be the extra material that would need to be accounted for but it wold be easier I think and safer seeing as that's how you would do it conventionally. Link to comment Share on other sites More sharing options...
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