Short Stroke - Project - Dyno-tastic
Turbo Mini Forums

A short stroke crank won't flex as much as a standard or long stroke crank so won't put as much strain on the centre main.

Just a guess.

Belts and braces tho, relatively inexpensive mod for the reassurance surely.

I have no experience with the sa crank, but on researching crank strength in general I am sure the sa crank is considered one of the strongest cranks for two reasons.

With the large diameter bearing sizes and the short stroke there is considerable main bearing to big end overlap. (If you look down the length of the crank you should see this). This provides a lot of strength and stiffness to the crank.

So the shorter stroke and overlap of the bearing diameters mean the crank is strong.

Personally I would also run a centre main strap too, as mentioned it is a cheap modification designed to strop the centre man cap flexing.

I was thinking the same, but i suspect V also thinks that my charger will run out of puff before any super high RPM's are reached, but lets see :)

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

cant that be solved with a different size pulley? maybe less effectief in the low revs then but think the short stroke would make up for this?

you can do anything if you set your mind to it...
i rather blow it up winning than keep it together losing.

finish date set for project 1... march 2018

personally I don't fit straps on any engines. Why would milling a bunch of material of the centre main and adding some steel bar make things stronger? Steel caps yes, but a strap? Old gospel.
Those who preach the gains of a strap say it's because the long stroke of the 1275 flexing of the crank. The SA crank doesn't flex.
Ask Dave Wells of SH how many of his engines that uses main straps? Who's winning Miglias and FIA races? His engines.

Just sayin'

When that is said, I ALWAYS fit these.

https://www.ebay.co.uk/itm/291409493605

Edited by Vegard on 7th Jan, 2017.

So I had a couple of hours in the garage this evening. I stripped down a spare gearbox casing that I had. I had driven this gearbox for a short period of time and it was very crunchy.

You could tell it had been stripped previously, the gears and bearings all looked good as it came apart, I was thinking it was strange until I found this...

and then realised the previous person had left out the bearing that fits in the first motion shaft... pisser, needs a new shaft as its now a bit chewed up.

check this bulk ring out..

Edited by gr4h4m on 7th Jan, 2017.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Regarding the main strap. Why not fit some proper high tensile bolts and washers to the centre main cap ?
I think the main issue with failures is usually when the standard bolts are used without washers or soft washers. The bolts chew into the cap or washers and lose tension/torque, allowing the cap to shuffle at high rpm.
What do others think ?

Phil.

WWW.TURBO-MINI.COM

I must admit I have ordered the set of washers that V posted.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Well, things move on, I have the block back from the Headshop Uk in Warrington. The block has been bored to +40, new cam bearings, decked, 11 stud and main cap machined for a strap. All looks nice.

The spare gearbox casing has been soaking and had a bit of a scrub.



I also had a little chat with our very own Fast Carl, who has made me a set of St10's however, these are not sandwich mount... I must admit I love the way they have turned out!

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Glad to see it coming together mate. You going to Bingley ?

Phil.

WWW.TURBO-MINI.COM

yep, shotgun with Colin. See you there?

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Yes mate.

Phil.

WWW.TURBO-MINI.COM

Very nice.

Look forward to seeing the wheels all built up.

Got a bench top parts cleaner today, does a great job with the small parts!

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

ok as an update. I have been cleaning, cleaning, and more cleaning the gearbox case.
I forgot how much time you need to clean stuff.
I also forgot how much checking and selecting parts, when building a new engine, its a pain in the ass....

Anyhow, I need to get the head off the old engine, hand it over to Turbophil to tickle it ready for the new application. i.e more revs.

As for the budget, its past don't tell the wife phase and firmly into the I don't even want to know phase, thats getting close to the bank manager not wanting to know phase...

Luckily (if you can call it that) I have had a security incident on my card so that I cant use it online, well thats what the bank said I think they were trying to reduce the spend on this build...

I stopped short of ordering a new cam and I will use the existing. I will also use the existing 4 pin diff. I was trying to keep the old engine complete so that I could maybe sell it on. I think now I will just keep the old lump in case this one ends up on the dyno floor or ceiling....

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Oh cock....

After scrubbing the shit out of the case it's no good.
I put the main shaft together tonight and thought I would install it in the case, all was going well then I went to install the bearing and the bugger slipped straight in.... and then spun in the hole.. balls...

Need a new case

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Hey Graham, first-up--> great choice of eng design BTW it`s one we have been procuring & sourcing parts & designing for a long time now, i`ll get to finish it one day

& on the auto-to-manual oil pump adapt plate, it looks like one of mine yeah?

& on the center main strap thing,,, we rarely use them, only if the customer demands it (even tho we do try to talk people out of using them) the theory is that the cranks flex (yes, obviously) but the problem becomes where the web of the crank works on the thrusts, which in-turn fatigues the bolts,,, so a machined cap & longer bolts isn`t really the answer as a longer bolt is weaker & a machined cap is also weaker (imo)

so what we do is--> fit std cap, decent quality std-length bolts, but then we make the lower thrusts really thin, simply there to hold the upper thrusts in place, but thinning them right down makes sure that the crank (when it flexes) will not touch the lower thrusts, therefor the bolts wont be worked-on & fatigue. simple.

my dad started doing things this way back in about 1965 & wev`e built every engine since just like that. . . & so far (touch-wood) we havn`t had a center main failure nor have we had any center main bolt problem. & we have rev`d some of our full race engines to 10,000rpms for quite a long time (especially in our 1415cc stroker speedway donks)

so please don`t believe too many people when it comes to revs (or a lack therfor) if long stroke engines can go past 10, then short =stroke donks can too again-> simple

keep up the good work mate

& if anyone wants any auto-to-manual oil pump adaptor plates we have had hundreds of them machined up

we also make thicker primary gear thrusts

we also make Cooper "S" fuel pump breather rivets

oh what am i talking about--> we make heaps n heaps of stuff here at ReadSpeed Mini Mecca Pty/Ltd
cheers
Matt
Bne, Aust

www.miniman.com.au

"""LazyGoodForNothingSmartArseKnowItAllBackYardMiniMechanic"""

Hi Matt I did order it from Aus. So it must be one of yours.
In the end I have got hold of a new block so the auto is sat on the garage floor.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Has anyone had issues with the retaining plate fitting into a new minispares layshaft? I would have thought it would be an easy fit as it's will have worn a little?

Scrap that I have just found out its a standard shaft. Last time I created my own rebuild kit rather than buying the off the shelf and it works out much better value....

Edited by gr4h4m on 5th Feb, 2017.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

So I have got to the dry build and have a big issue, the Rods I have been sent have the wrong BE size. They are for the CooperS from what I can tell, I think the trader had an issue with his original order. I have emailed him to see if he can help., but with the issue I had with the wrong piston fitment and having to get the pistons machined I should have checked the BE but the crank was at the first machine shop! Fingers crossed.

What to people advise on endfloat for a short stroke? with the std thrusts I have 0.115mm so just over 4 thou?

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Shouldnt be to hard to source std rods tho, at least you got the ones worth more so by the time you've swapped them you should be in profit.

Cant remember the endfloat being any different from standard

So I have had a few setbacks, stuff not fitting, wrong stuff being sent etc..

I have swapped the rods, and the layshaft, sent a cometic gasket back to MED after ringing up and ordering a +60 to be sent a a +40 when I called and said they had sent the wrong one I was told they sell them to fit the overbore but all the same thickness. I did point out most people order these gaskets in thickness, but either wya I have sent it back for a refund, which they have been slow with!

I have the gearbox together and the gearkit in the new gearbox case. The speedo side cover cracked when I torqued it down.. more cleaning then.. I have also ordered a new trust washer for the idler gear as I need some more clearance after trying the thick green gasket but still no good.

I managed to get the diff in and ready to go...

So I have a few days off next week so hopefully I have get it all together and in the car...

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!