Piers Bowlan Posted January 14, 2019 Share Posted January 14, 2019 What fuel were you using in your APS91 Steve? Quote Link to comment Share on other sites More sharing options...
Jon H Posted January 14, 2019 Share Posted January 14, 2019 I pressed the pin out of an ASP 52 crank once and found its not the same size all the way along. The actual crank pin is a small o/d than the part pressed into the shaft. I didnt measure the sizes, but the conrod would only fit on one end of the pin Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted January 14, 2019 Author Share Posted January 14, 2019 Ref the bust APS 61 crank The pin in the crank measures 0.228" ( pressed out ) the broken off pin conrod end 0.215" So yes the "pin " is stepped , by 13 thou and if a sharp edge would lead to a nice stress raiser sorry to you metric guys ! Pete W Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 14, 2019 Share Posted January 14, 2019 Posted by Piers Bowlan on 14/01/2019 09:30:50: What fuel were you using in your APS91 Steve? Southern Modelcraft MoGlow 5% has been my fuel of choice for many years Piers....it's 15% synthetic & 2% castor but I've recently bought some of their Laser mix which is just 15% (synthetic) oil. Not used it much as yet but I believe that a lower oil content fuel is the way to go....especially with the improvements in oils over the years.... I have fond memories of Model Techniques Dynaglo which I used many many years ago & is, I think, just 9% oil.....my engines used to go like stink on that stuff but everyone said "Ooooh that's not enough oil..." & I kind of got cold feet & switched away from it.... Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted January 22, 2019 Share Posted January 22, 2019 Posted by Pete Willbourn on 14/01/2019 11:52:25: Ref the bust APS 61 crank So yes the "pin " is stepped , by 13 thou and if a sharp edge would lead to a nice stress raiser sorry to you metric guys ! Pete W Very interesting to note . the step will of course increase the stress . I have replaced the crank with an OS 52 which is a straight swap but never had the broken part of the crank pin for comparison . I have replaced the crank pin in an ASP 61 two stroke and that was a straight pin . I would still look at replacing the pin with a straight pin and making the con rod fit the pin with a new bush . There looks to be enough metal to take the mod . Has anyone tried it ? ps. Don't have to apologise for imperial . "We are moving into the metric age inch by inch " PPS Have sent a PM re OS crank. Edited By Engine Doctor on 22/01/2019 10:50:19 Quote Link to comment Share on other sites More sharing options...
Jon H Posted January 22, 2019 Share Posted January 22, 2019 If you have managed to get the pin out i have that bent asp52 crank still kicking about. I can press the pin back out and send it? Quote Link to comment Share on other sites More sharing options...
brian sylvester 1 Posted February 11, 2019 Share Posted February 11, 2019 had broken crankpin on my asp 91 fourstroke now rebuilt with new crank not run the engine yet but it seems to turn over ok. so do i run it or put it on ebay? brian Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted February 11, 2019 Author Share Posted February 11, 2019 with the help of E.D. ,I have fitted an OS crank and it ran yesterday and was "Spot on "! I recon smoother ? so thanks to all for their help Pete Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted February 11, 2019 Author Share Posted February 11, 2019 and to Laser Jon , thanks for the offer of a crank pin , but see above , But bear in mind for the future that between us we have the solution , should someone else suffer from this problem . I am banking on the OS crank no failing , it is in fact a far better quality manufacture ! cheers Pete W Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted February 11, 2019 Share Posted February 11, 2019 Posted by Engine Doctor on 22/01/2019 10:47:04: Posted by Pete Willbourn on 14/01/2019 11:52:25: Ref the bust APS 61 crank So yes the "pin " is stepped , by 13 thou and if a sharp edge would lead to a nice stress raiser sorry to you metric guys ! Pete W Very interesting to note . the step will of course increase the stress . I have replaced the crank with an OS 52 which is a straight swap but never had the broken part of the crank pin for comparison . I have replaced the crank pin in an ASP 61 two stroke and that was a straight pin . I would still look at replacing the pin with a straight pin and making the con rod fit the pin with a new bush . There looks to be enough metal to take the mod . Has anyone tried it ? ps. Don't have to apologise for imperial . "We are moving into the metric age inch by inch " PPS Have sent a PM re OS crank. Edited By Engine Doctor on 22/01/2019 10:50:19 I was all set to poo poo the suggestion that the pin was stepped and suggest the difference was just wear but having just checked my bits, I'm forced to agree! The pressed in section on mine measures 0.2275" and will not fit into the big end - and there is definite evidence of a significant step at the point where it broke. What an odd design! I would think that there's sufficient bearing material to ream the existing bush, but 0.2275" is @ 5.78mm so the interference fit in the crankshaft must be compromised if using a 5.8mm pin...I think the minimum difference is 0.03 mm if I've interpreted the tolerance information for a light press fit correctly. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted February 11, 2019 Share Posted February 11, 2019 Posted by brian sylvester 1 on 11/02/2019 14:07:07: had broken crankpin on my asp 91 fourstroke now rebuilt with new crank ..... brian Blimey Brian that IS a coincidence.....I rebuilt MY ASP91 fourstroke that had suffered a similar fate this weekend.....new crank, con-rod & bearings (the ones in it felt OK but I can't help feeling the rear one was probably full of aluminium shavings) Not run as yet but turns over nicely.... Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.