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Stroking a Motor
https://ausmini.com/forums/viewtopic.php?f=5&t=5265		 Page 1 of 3
Author:  Chris [ Thu Mar 03, 2005 9:04 pm ]
Post subject:  Stroking a Motor
I was making enquiries today about boring my motor and the guy I was speaking to suggested i stroke it instead. I wanted to bore it from its present 1330 to 1360 but he suggested I leave it at +060 and stroke it to get the capacity thus leaving room to bore it in the future. It sounds like the price to do both would be similar. Anyone done this? How much does the stroking increase capaciy? BTW this guy knows heaps about Minis and has an immaculate black van.
Author:  CLUBMAN [ Thu Mar 03, 2005 9:08 pm ]
Post subject: 
the extra cost of the crank and rods,you could boar to 1360,and buy another block and bore it out again....
would b good but EXPENCIVE :cry:
Author:  Chris [ Thu Mar 03, 2005 9:15 pm ]
Post subject: 
CLUBMAN wrote:
the extra cost of the crank and rods,you could boar to 1360,and buy another block and bore it out again....
would b good but EXPENCIVE :cry:


Not by the quote I was given today. It would be only marginally more expensive.
Author:  CLUBMAN [ Thu Mar 03, 2005 9:16 pm ]
Post subject: 
im told the other thing wrong with em is that they rev slower due to the bore/stroke ratio
Author:  kazjim [ Thu Mar 03, 2005 9:28 pm ]
Post subject: 
But with the extra Torque, you can gear them higher so you dont NEED To rev them as hard .....

8)

J
Author:  Chris [ Thu Mar 03, 2005 9:31 pm ]
Post subject: 
kazjim wrote:
But with the extra Torque, you can gear them higher so you dont NEED To rev them as hard .....

8)

J


Thats the whole point of course. I want to run a 3.1 diff. Anyone got one or do I have to buy it OS?
Author:  drmini in aust [ Fri Mar 04, 2005 6:20 am ]
Post subject: 
Stroking by using a large journal crank offset ground to 1.625" does weaken them a bit. They are only EN16 material....

I considered doing my new one that way to get from 1360 to 1405 (I have a suitable crank already) but Graham Russell suggested as I have a good S crank & rods, as I want to rev it, use them. :wink:
So a high windin' 1360 it is. 8)
Author:  Chris [ Fri Mar 04, 2005 9:45 am ]
Post subject: 
drmini in aust wrote:
Stroking by using a large journal crank offset ground to 1.625" does weaken them a bit. They are only EN16 material....

I considered doing my new one that way to get from 1360 to 1405 (I have a suitable crank already) but Graham Russell suggested as I have a good S crank & rods, as I want to rev it, use them. :wink:
So a high windin' 1360 it is. 8)


After being involved in karting and 2 strokes I have gone right off revving motors hard. The piston speeds get to high and the wear rate goes through the roof. This is going to be driven every day so it has to last. Even if I do not stroke it I will put a low limit on the redline. I have a standard car which I drive everyday and it goes to 8000 rpm no worries so revs really have no fascination for me at all. The only good thing about revving a motor that I can see is it gives more flexibility in gearing and as this is not a racing car that is not an issue.
Author:  drmini in aust [ Fri Mar 04, 2005 11:28 am ]
Post subject: 
I've seen my share of busted cranks- mostly EN16 ones and that included a small crankpin 1100S one that went bang! 20,000 miles after a regrind.

S crank (EN40B material) is stronger and I've got 2 good ones, so I'll use it. :wink:
It ain't broke so I won't fix it. 8)
Author:  Chris [ Fri Mar 04, 2005 9:20 pm ]
Post subject: 
drmini in aust wrote:
I've seen my share of busted cranks- mostly EN16 ones and that included a small crankpin 1100S one that went bang! 20,000 miles after a regrind.

S crank (EN40B material) is stronger and I've got 2 good ones, so I'll use it. :wink:
It ain't broke so I won't fix it. 8)


Do you get your cranks crack tested Doc? A big problem is the regrind doesen't get a good radius on the journal or some dope drops it or hits it with something. People just do not understand the tender care cranks require.
Author:  drmini in aust [ Fri Mar 04, 2005 9:34 pm ]
Post subject: 
Chris wrote:
drmini in aust wrote:
I've seen my share of busted cranks- mostly EN16 ones and that included a small crankpin 1100S one that went bang! 20,000 miles after a regrind.

S crank (EN40B material) is stronger and I've got 2 good ones, so I'll use it. :wink:
It ain't broke so I won't fix it. 8)


Do you get your cranks crack tested Doc? A big problem is the regrind doesen't get a good radius on the journal or some dope drops it or hits it with something. People just do not understand the tender care cranks require.

Yep that 1100S one was crack tested. You might be right about the radius though- it's real important and some crank grinders just don't care!

I used to magnaflux cranks (eons ago when I worked at the railways)- these days I `ring' test them (Graham Russell does this too) then dyechek them if any doubt.
If you stand a crank on end and tap one of the top webs lightly with a spanner, it will ring like a bell. IF it's not cracked... :shock:
repeat for other end.
If it sounds dull and flat, it's a dud. :wink:
Author:  TheMiniMan [ Sat Mar 05, 2005 10:46 am ]
Post subject: 
There`s absolutely no problem doin a stroker donk for revs,,, they are strong as & can handle 8000rpms all day every day (when built correctly)

we`ve been doin stroker donks since the first ever large journal crank hit Australia (That`s a long time)

not one of "OUR" cranks has given any trouble in all that time (& we`ve probly built more stroker mini donks than just about anyone in Aust), we road them, we rally them & we full race them, fark, my own race 1415cc donk qite regularly hit 9000rpms & there`s still nothing wrong with that crank to this day!!!!!!!!

They truely are a wonderfull, magnificent road donk & i still don`t recoment talling up the gearing, we still fit 3.7 or 3.6 ratios to our roadies, for a number of reasons,,,one of which is simple putting along the suburban streets with a 3.4 & you`re speeding,,, fit a 3.7 or 3.6 & youre just on the speed limit & happilly just putting along minding your own business,,,,if you want to get up & go, well, just push the pedal, no need for down shift at all,,,there are plenty of other reasons as well,,,EG: the word """accelleration""" & there`s even more reasons concerning the vibration factors at certain revs, i won`t go on & on about all that cause i could be here typing about it all day :-)

if people would bother to do their homework on the gearing of these little wonders of the motoring industry, then they`d realize by going tall,(EG:3.4,,,3.2,,,3.1,,,2.9 etc) they`re killing their torque & accelleration & are "DEFINATELY" not gaining any top speed by doing so.

with a well built 1415cc stroker (our own designed 73mm pistons & 1/8" stroker crank) will happilly run for literally years & years & years,,,we have customers that we`ve done strokers over 20 years ago & they`re still fangin around today.

Yes, long term exccessive revs can wear them out, but that`s the same with any car,,,"Exccessive" revs will wear any engine out quite quick,,,but 7500rpms in a road donk is not exccessive in my books as my 1510cc stroker has done so for over 8 years now...you only have to look at all the late jap cars , happy to hit 8000rpms for years & years, they`re no different.

proof is in the pudding boys & girls, you just need to know how to build em right :-)

we did one roady for a mate of mine back in the 70s & it regularly hit 8000rpms,,,addmittedly the road cam didn`t allow much power after 7000 but he continually hit 8000rpms & it`s still alive today & i actually took the 0-1600cc tourng car lap record at Echo valley hillclimb with it,,, pump fuel,,, 25/65 cam ,,,& all roady stuff with single carb & yep,,,8000rpms all day.

now someone else try to tell me that stroker mini donks don`t rev & see what happens!!!!!!!!!!!!!!!!!!!!!!!!!!! go on ,,,i dare you!!!!!!!!!!!!!!!!!

crickey!!!...now my fingers hurt :-)
Author:  drmini in aust [ Sat Mar 05, 2005 11:39 am ]
Post subject: 
I agree with you about the tall diff ratios Matt- I'm pulling the 3.4 out and fitting a 3.6 to the 1360 this time! :P
Author:  Chris [ Sat Mar 05, 2005 12:28 pm ]
Post subject: 
Matt, I am building a motor which will rarely see a suburban speed limit and will spend most of its life at 110-120. I live in the bush so to speak and never go into the metro area. If I do I can use another car. Can you give me the RPM per 10kph in top with a 3.44 on 10's using a mini k box? This car is going to be doing 20,000km a year and I want it to last. I am not into pulling motors out of cars if I don't have to. Any advice gratefully accepted.
Author:  drmini in aust [ Sat Mar 05, 2005 6:49 pm ]
Post subject: 
Chris,
Stock Oz Mini box (any) with 3.44 diff with 165/70-10 tyres = ~16.1 MPH/1000 = 25.91 KMH/1000.... 8)
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