[Mk2] [Turbo] 3SGTE Toughened Crank ?!

[Dangerous]

Don't know if it's any help or relation but FYI.... When my engine build was being specced they modified the block (deleted the the oem water- oil cooler) some how to give better oil pressure in the bottom end thus keeping big ends and crank more lubricated at higher stressed loads... For reliability.... Pretty sure they got the idea from fennys celica.... Just an idea??....

Also had the crank polish/lightened,knife edged and balanced...

[^Trickster^]

If you want higher pressure just shim the oil pump. A lot of people think it doesn't make a difference, there used to be a company that made a high flow/volume pump, think it was toga or something. Anyway I shim my pump with a 1mm shim for higher pressure and never have a problem.

Graeme

[Dangerous]

If you want higher pressure just shim the oil pump. A lot of people think it doesn't make a difference, there used to be a company that made a high flow/volume pump, think it was toga or something. Anyway I shim my pump with a 1mm shim for higher pressure and never have a problem.

Graeme

Yeah I know you can get higher oil pressure pumps and stuff.. My engine builder said that shimming the oem pump wasn't the way to go.. Just his opinion... Glad it works ok for you... Can u see the point I'm trying to make..??? Better lubrication/less stress wear on internals...???...food for thought??.. I though I was a good idea anyway....But then again I am on my 3rd block!!

[ashley]

Would lightening/ knife edging a crank make it more or less likely to fail?

On one hand I can imagine removing material might weaken it...

But on the other hand...would reducing it's mass, and so it's inertia, reduce the stresses on it at higher rpm? One of my concerns using a 5S crank is the increased mass, and so the higher forces involved than a standard crank at higher rpms.

And likewise there would be less mass to be accelerated as boost kicks in hard, and so presumably less stress across the crank if it's lighter...?


Or am I talking complete guff

[Dangerous]

Would lightening/ knife edging a crank make it more or less likely to fail?

On one hand I can imagine removing material might weaken it...

But on the other hand...would reducing it's mass, and so it's inertia, reduce the stresses on it at higher rpm? One of my concerns using a 5S crank is the increased mass, and so the higher forces involved than a standard crank at higher rpms.

And likewise there would be less mass to be accelerated as boost kicks in hard, and so presumably less stress across the crank if it's lighter...?


Or am I talking complete guff

I think the general idea of knife edging is to help how the crank spins through the oil... Lightning and balancing come together...with polishing.. Metal is only removed from the lobes of the crank not the journals... I dont know if has weekend the overall strength of the crank... But I believe your theory to be correct in it's all about reducing inertia thus stress a high rpm.

[Dangerous]

Comes on boost HARD!!!!!

[bobhatton]

Its all down to balance.
The crank webs have to balance the pistons and rods but counterweights are never added to 4 cylinder cranks, they are just balanced on there own and so are the pistons and rods.

I have Jack Brabham’s old balancing machine and must try and get it working again and see what I can do with balancing cranks other ways.

[ashley]

Yeah- I get that knife edging helps the lobes cut through the oil, and so reducing resistance to it turning....I guess that's gotta help reduce stress on the crank as well.

Just wondered whether 'working' a crank will inherently weaken it

Still kinda wish I'd knife edged my 5s crank (despite being assured it wasn't worth it)...the 3s rev'd superbly with a lightened crank- it was lurvely


Is your motor boosting HARD yet mate?!

[^Trickster^]

Really the crank should not be cutting through the oil at all, that's why the sump baffled. I never understood why people knife edged the crank, I can understand balancing to a certain extent. You need the crank to have material on it for counter balancing, I saw a guy take so much off it looked more like a big crankshaft, engine did not last long either. The crank spins, it has no other movement besides when the clutch drops power onto it, and our engines don't suffer from crank walk either.

I think its just bad luck, how many high powered 3sgte motors are out there spinning away? You always here the bad stories and they stand out the most, does not mean we all need to start pulling the bottom end for balancing and lubrication upgrades.

I think a good line bore, unground crank, good shells and arp main studs is all you need, anything can break, its luck of the draw.

Edit: the crank doesn't sit in oil for those who don't realise that

[ashley]

Really the crank should not be cutting through the oil at all, that's why the sump baffled.

Does it not help it cut through the oil that is pouring down from the cylinders (from the oil squirters)?

Edit: for the crank to be actually sitting in oil you'd have massively over filled the oil level

[^Trickster^]

Do you think the crank would actually have a problem cutting through oil drilling down the inside of the cylinders and block?

It's spinning 100 times per second at 6krpm with an unbelievable amount of torque, oil is not getting a look in when it come to resistance of turning

You could put your hand in, think that would stop it? Lol

[ashley]

Tis a good point, but on the other hand knife edging a crank is a recognised modification so there is presumably some benefit from doing it? I've always been told it 'helps reduce resistance on the crank by cutting through the oil'...as you say: the crank should not actually be submerged in oil....so what other oil would it be designed to help cut through?

I'm guessing that at full chat there is a significant volume of oil around the crank that is in the process of draining down into the sump- certainly enough that the crank would effectively be running in oil in these conditions...and the knife edging would help cut through this...?

Otherwise why would it be a recognised performance enhancing modification?

...and no, I won't be putting my hand (or any other appendage) in there to test this

[bobhatton]

Do you think the crank would actually have a problem cutting through oil drilling down the inside of the cylinders and block?

It's spinning 100 times per second at 6krpm with an unbelievable amount of torque, oil is not getting a look in when it come to resistance of turning

You could put your hand in, think that would stop it? Lol

That is not quite right.

The crank with have about 6” dia or so of oil wrapped around it and having a sharp edge to the crank helps to cut some of that oil off.

When I build my dry sump I will be using a scraper that will be a very tight fit to the crank to strip all the oil off.

[^Trickster^]

I see the point, I just don't see it that beneficial sorry.

What would rather spend my money in other places, most people spend an absolute fortune and a large among of time with their car off the road doing all this stuff and then don't even make over 400hp so they are not breaking any records or pushing the boundaries of what is possible anyway, the stock crank works fine as it is, unless your doing something very different I would leave it alone.

I have only seen a fee 3sgte engines with dry sump, again another mod unnecessary for the most of us, would be nice to see your design and fabrication process.

[dawesy]

the reason cranks are knife edged is purely aerodynamic.
there is a mist of oil in the crankcase when the engine is running and the crank has to cut through that mist.
by giving it a more aerodynamic shape it will go through the air/oil mist a lot easier and less power lost.
it also reduces the weight of the crank considerably and because the material comes off the counter weight part there should be no loss of strength

[bobhatton]

It is far more that a mist of oil, the whole crank is wraped in oil as it comes out the bearings and down from the head. That is why a dry sump will give more power as the sump will strip a lot of the oil off the crank

[ashley]

I'm interested to know more....how does the dry sump help strip oil off the crank? I understand that it means you don't have the resevoir of oil in the sump that you normally have, but how does it actually help strip oil from the crank itself?