Long stroke cranks and their materials/limits.

[In the shed]

Hello fellow enthusiasts.

I'll resist the temptation to waffle too much.

My 1430 has a bit of a crap bottom end. It runs an EN16 A series crank with 84mm stroke. This ran a "holey" lightweight flywheel, cooper s backplate (normal) and rally clutch. It was balanced, but not worked in any other way. The centre main cap was as standard. The engine has done 3 races and has it's bores still hatched. S rods

I have picked up a Farndon 86mm fully worked crank....wedged, bladed, backdrilled, cross drilled, EN40B, the real bizz.

I am currently considering what flywheel to go for and in the interests of high revs and longevity (nothing else) I was considering something "extra ultralight". I am also interested in the subject of how fast I can spin this, what bearings I should use and what to look out for.

The internet is quite short of people talking about high performance long stroke engines and I suppose they are old hat.

I have virtually learned the yellow bible, what I am interested in are people's real world anecdotes and wisdom.

[Jono]

have a word with Lance Foster or Ian Sandwith at Green and White Mini Spares.

[ianh1968]

In the shed, please post back if you get some answers...

I have a 74 x 86 and have asked myself the same questions.

Ian

[Red Mist]

I too have a 74 x 86 set up.

It revs happilly to 8k, but it is an all steel bottom end and has the all important 4-bolt centre main strap which I'm told is essential if you want high revs.

My flywheel is just a regular lightweight item and seems perfect for the job.

Will need to have look to see what bearings we used as I can't remember!

[Vegard]

Swiftune have built many 310cammed 1460s, maybe they could shed some light on this?

[Oldskoolbaby]

As far as I'm aware, LynxAE produce the lightest flywheel and clutch setup. It isn't cheap but the life of the crank tail is heavily improved on compared to almost all others. Something that is well worth considering on an expensive, non original crank.

[251 ENG]

The swiftune DC5 is by far the best setup for long stroke cranks .

[wantafaster1]

My standard stroke is making me feel inadequate, not to mention all the chat about rods elsewhere!

[wantafaster1]

On a more serious level, a friend used to rallycross a 1600 a series. The build sounds frightening, with the block well ground away inside, araldite on the outside of the box to retain oil, bits ground off the rods etc.
Everyone advised him not to bother with it, but it ended up a successful car. Enough power to get off the line in second, and he says he just revved it until a big vibration came into it and then changed gear.
After a few years another guy bought it. It never grenaded.

[In the shed]

The whole concept of asbo is that it isn't a £15000 car and it's not a £10000 engine/box. It's an old tuned mini.

I will probably go for a swifty featherweight flywheel, because it speaks the same language as the car.

I don't know why anyone in their right mind would bend £4k on a crank, rods and pistons in a mini. That's like taking Dawn French and spending £100k on plastic surgery for her. You'd be better off starting with a Kate Moss and buying her some lipstick......if you catch my drift.

I've read some things about big engines in vizard's bible. I think it's probably an idea to revisit them. I've also read some stuff about cranks coming apart in full bore situations.

It would be good to say "a forged EN40B crank ran in my car regularly up to 9000rpm and was fine after 20000 miles, but wore it's widger shortly after".

The name of the game with this thing is to select parts properly (at the right price) build it carefully, maintain it well and enjoy it for a long time. I don't want to open the taps only for the flywheel to chop my foot off.

[ianh1968]

The swiftune DC5 is by far the best setup for long stroke cranks .

Yes, but they are not cheap and come as a set which includes
special rods and special pistons. You either have to have the
whole setup, or none of it!

I looked at the pictures and saw that the pistons were very short
and wondered how long these would last in a road-going engine.

With the '60's Hillman Imp + 1098 = 1216cc setup, the pistons are
short and because of "piston rock", the bores would wear quite quickly.
When I saw the Swiftune kit, I wondered if this would be the case here,
as well.

This is what I have...

201309MiniEngine-160.jpg

The rod bolts are ARP.
The centre main cap was milled, then surface ground flat.
The centre main strap was also surface ground flat.
The studs are some kind of generic "High Tensile" ones.
The nuts are ARP.
The front and rear bearings have standard type bolts as I
could not get the ARP studs/nuts to go in without 'box mods.
(Needed to get it going quickly, so that's a "one-day" job)
The flywheel is a MiniSport 4.4Kg one (MiniSpares were "Out-of-Stock")
The flywheel was balanced, then the diaphragm and backplate were
added with spacers - The backplate was then "corrected".
The bearings are Vandervell (Is there anything else?)
They are also the later/Turbo type that have one grooved shell
and one plain one for each pair. Needed to file a "tag" for each.
The rods have been done to the much derided "same weight of
sections" method. Despite them being "not balanced" the engine
runs very smoothly at all RPM up to my self-imposed normal limit
of 6500RPM. Mostly this limit was decided because I haven't
dyno'd it yet as I've only just got a sensible 11:1 "low compression"
head on it. The 13:1 I had before was a serious spec-mismatch
with the cam...
The pulley is the two piece 'S' type one, which has also been balanced.

Once I've had a session on the dyno, I expect that 7000RPM would
be OK.

Ian

[minibitz]

I don't know why anyone in their right mind would bend £4k on a crank, rods and pistons in a mini. That's like taking Dawn French and spending £100k on plastic surgery for her. You'd be better off starting with a Kate Moss and buying her some lipstick......if you catch my drift.

I'm not sure this analogy adds up. I mean, on the face of it your Dawn French crank might not seem like a hot bet. However, far less likely to have been raced or rallied so still has a bit of life left whereas your Kate Moss crank has seen more than a few seasons of hard action and could let go on you at any moment.

[Oldskoolbaby]

The reason people spend £4k on a bottom end isn't for pub talk figures but because thats what they are prepared to shell out to get higher up the grid on a reliable basis. Not only that but if you are looking for a high revving engine, everything has a knock on effect so the costs spiral ie fit a 4 bolt center main, then price in for line boring. Want a stroked crank, then price for S or after market rods, then price for pistons that sit correctly at deck height. Want a better rod ratio, then its new rods and pistons. All of which adds to better reliability which in turn may save you in the long run and keep you on ghe grid more regulary.

[Vegard]

What I cannot understand is why all long strokes have got 1.625" journals. Wouldn't it be MUCH better to use the 1.75" ones?
I mean the billet cranks, not the offset ground ones of course.

[rich@minispares.com]

What I cannot understand is why all long strokes have got 1.625" journals. Wouldn't it be MUCH better to use the 1.75" ones?
I mean the billet cranks, not the offset ground ones of course.

wouldn't the big journals just chew through the block and gearcase though?

[69k1100]

Also greater surface area so more drag.

[Vegard]

What I cannot understand is why all long strokes have got 1.625" journals. Wouldn't it be MUCH better to use the 1.75" ones?
I mean the billet cranks, not the offset ground ones of course.

wouldn't the big journals just chew through the block and gearcase though?

With a proper new H-profile rod, the OD isn't that much bigger??

Also greater surface area so more drag.

Well theoreticly, but a 1.75" journal is not large viewed against the 81mm stroke, compared to other engines. And, the stock 1275 has got it

[Oldskoolbaby]

I should imagine the reason the aftermarket cranks don't have the bigger bearings is because they are made of better, stronger material so don't require bigger crank pins. You will also have more weight with bigger pins along with the added distance from the cranks center line. Neither of which is beneficial apart from obviously increasing the capacity. Stock S rods are fine for the job in hand though.

[In the shed]

I think I'm going to chuck some H beam rods on it and probably a steel featherweight flywheel. I might have a rethink of the current cam/S rockers situation as well. Will go for a strap, rather than a cap. My hunch says that the centre of mass of the featherweight is more central than the KAD alloy, thus having less inertia and leverage when/if it starts precessing.

I dug my Vizard bible out last night and had a read. I am no further forward. Although it will be exciting.

DCOE will be on ebay at some point (early italian one needing a proper rebuild - with kit)

[251 ENG]

The point of the SwiftuneDC5 is to have a long stroke crank and keep the rod ratio to something reliable .

Short rods with long stroke cranks tend to try and punch the rod / piston out of the side of the block.

MED does a long stroke , long rod , short compression height but without the false main crank and still has the offset big end rods .

These are all good idea,s for reliably big mini engine,s .

We do a lot of machining on imps and the rod ratio is crap.

Basically if you can,t get a taller block or want the hassle of a spacer plate it,s the way to go.