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ASP 61FS Just Stopped !!

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GrahamWh13/01/2019 20:40:59
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Thanks Pete.

Engine Doctor13/01/2019 20:44:07
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Posted by Martin Harris on 12/01/2019 19:32:16:

Thanks ED - I'd already checked them as they are my first call for bearings (they've already supplied the bearings for this engine!) but they don't list anything in 5.8mm diameter. I have found one place but the postage charges are a bit unreasonable so, with the slight doubt over the measurement, I'm wondering whether to bother at the moment (engine saved from the club bonfire and no home waiting with an empty engine bay). It was a useful exercise pressing out the pin which will definitely be borne in mind if I have a similar problem with one of my "working" engines...or find a need for a 61.

Edited By Martin Harris on 12/01/2019 19:44:04

Hi Martin couldn't you drill/ream the crank to a tight interference fit for a 6 mm roller ? the big end should have enough metal to be reamed to 6 mm .

Engine Doctor13/01/2019 21:02:28
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hello Martin just found this supplier . They list a 5.8 mm roller cost £1-73

Jonathan W13/01/2019 21:59:31
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You can also get HSS drill blanks in pretty much any size. I'm not sure if HSS is suitable for the cyclic loading experienced by a crank pin, but maybe worth a shot. Try a local engineer's supplies, or the usual online search.

Try these guys: https://www.tracytools.com/high-speed-drill-blanks

Edited By Jonathan W on 13/01/2019 22:01:31

Edited By Jonathan W on 13/01/2019 22:02:11

Martin Harris13/01/2019 22:43:30
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Thanks for the interest ED (and Jonathan) - I'd already filed them under the (with apologies to Ken Anderson) "when I need a 61 I'll give it a punt" department as postage from this supplier is "from" £5.45 and plus VAT on both prices and I have slight doubt about the old pin size - odd that an interference fit pin measures 0.015 mm under 5.8 mm diameter...but perhaps both my micrometers are wrong!

Simply Bearings, on the other hand, have a terrific free (has always been next day) delivery policy which is why I normally use them - shame they don't stock them...

Edited By Martin Harris on 13/01/2019 22:45:16

Piers Bowlan14/01/2019 09:30:50
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What fuel were you using in your APS91 Steve?

Jon - Laser Engines14/01/2019 11:05:21
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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

Stuphedd14/01/2019 11:52:25
610 forum posts
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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

Steve Hargreaves - Moderator14/01/2019 20:00:32
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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....

Engine Doctor22/01/2019 10:47:04
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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

Jon - Laser Engines22/01/2019 12:15:17
4312 forum posts
159 photos

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?

brian sylvester 111/02/2019 14:07:07
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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

Stuphedd11/02/2019 17:03:53
610 forum posts
320 photos

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 yes

Pete

Stuphedd11/02/2019 17:09:22
610 forum posts
320 photos

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

Martin Harris11/02/2019 17:10:50
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8162 forum posts
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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.

Steve Hargreaves - Moderator11/02/2019 19:46:31
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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....

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