fujack

Theres no prize for the winner!
... but who can spot whats wrong with my cranks?



http://i67.photobucket.com/albums/h2...k/DSC_9130.jpg

http://i67.photobucket.com/albums/h2...k/DSC_9126.jpg

http://i67.photobucket.com/albums/h2...k/DSC_9122.jpg

http://i67.photobucket.com/albums/h2...k/DSC_9121.jpg

http://i67.photobucket.com/albums/h2...k/DSC_9140.jpg

Quatto

Those fillet radii look slightly odd, might explain the state of the thrust faces.

Looks like a fresh crank, has it been re-ground?

RON

Thrust surfaces are fubared.....

fujack

Yes it had been reground and lasted under 600 miles of running in! what would you say went wrong i.e. what would AND could course this? I think i know but i just want to see what others say.

ZEN Performance

it's screwed. Get a new one, which you should have done in the first place. Regrinds are generally a no-no on subaru cranks.

Paul

p1mark

From this thread here, about regrinding cranks but with a few PSlewis interjections :-

https://www.scoobynet.com/general-te...ghlight=plasma


Is my post #96-


Quote:
Originally Posted by STI Craig
asssssssssssssssssss

i just rebuilt my engine my self and had the crank reground.

i have just run it in and in the next day or so im going book it in with with andy F to get it mapped

sould i be worried about it failing again as i will be expecting 350bhp.
im pooing myself now!!!! just cant aford to rebuild it again!!

also i have replace the maf, oil pump etc

It may be ok in the short term, but i feel you are on borrowed time. depends on how much they have taken off, and the finish/quality/geometry of the pin.

As normal APIdavid and Zen performance are right. Subaru Plasma nitride there cranks. It does leave a very thin hardness layer that is dependant on how long they are processed and gas mix etc, but judging by the cycle time they were using in the furnaces that i saw it will be very similiar to the cranks @ my place of work.

you are looking at around about 600 vickers (not especially hard, but enough) and this drops to around about 500 at 0.2mm depth.

so if you grind any more than say 0.3mm on diameter from the pin, you are seriously affecting hardness.

Plasma Nitriding steels will not have the carbon content (and there is other elements in there as well) to allow any kind of effective induction hardening of the ground pin. Induction hardening is a pain on cranks anyway, requiring pre stress relieving ops, and tempering and straightening ops after hardening.

The reason lots of jap cranks are made this way is simple - its very clean and controllable compared to more traditional methods.

The cranks are machined and ground (so are geometrically correct) before hardening. Plasma is such a comparitively low temp (520 deg) that no distortion takes place during hardening. Hardening is done in a controlled vacuum furnace, no mess/coolant/oil around.

As soon as they are out, a polish of the pins and mains to remove the white layer and you have a finished cranks.

The only japanese factory making cranks not using Plasma i have been to was a Nissan factory in Thailand. quite a few european manufacturers still induction harden though.

Carburising and nitride baths etc went out with the Ark for production, but still have there uses in the F1 and protoype industry.

In short, grinding a scoob crank is a long term recipe for disaster.

fujack

That wouldn't explain why the thrust has eaten into my crank tho, seeing that the thrust face wasn't machined .....or was it!

scoobyboy

did it have oversized shells in it? if so maybe they were to large in relation to the thrust side of it causing a heat build up.

p1mark

There are a number of ways of 'repairing' a crank. You can just regrind the journal, but you can also get it metal sprayed with a hard coating. Any overspray not moved on the thrust faces is a possibility.

Also if the thrust faces were damaged at the time of the original problem and they were not picked up by the builder. Another possibility is the oil holes were not cleaned properly after the initial grind, and particles have caused pickup on the thrust face.

Either way As Zen perf says, its fooked. Just get a new one and get it built properly.

fujack

lol i dont think im going to repair a crank thats been ground thats gone wrong thats shouldn't of been ground in the first place!

Here on this pic of the cranks thrust side have a good look at it and your see that the marks dont run round with the rotation of the crank so i dismiss the idea of tightness


http://i67.photobucket.com/albums/h2...k/DSC_9122.jpg

These marks can be seeing on all the side wall next to each main even on the back of the end you bolt the flywheel to!!!

p1mark

Are you talking about the machining marks on the inside/outside of all the webs?

They are a function of the machining process (called turn-broaching) and are there from manufacture. They are radially angled at a tangent from the crank centre-line simply as a function of the axis the cutter moves along while machining.

fujack

Yes, On the side the thrust runs on you can see scratch mark as if the grinding wheel has touched. I think this is why the thrust has worn in such a short time! I took it back to who ground it and he told me it wouldn't be a problem and that my car was detting and thats what made the thrust wear into the crank... hmmm maybe thats what made my tyre go flat on the back as well . I then asked if he would be happy putting a crank in with these marks and he said he would prob rub it with a bit of 600 wet and dry So there aint a problem but he would wet and dry it which to me is a bit of a bodge. So after about 20 mins of me holding myself back from punching him as he comes up with a number of excuses that could of worn it but not addressing the main question i wanted answered as to where the scratches came from. Then at the end of it all he tells me he didnt grind the crank! (i thought this was strange as he made out he was going to do the job) so i asked who did and he told me that the company know what their doing when it comes to subarus because they build big BHP engines, this still dont tell me how the scratches got there. Anyway, He said he would take the crank to them and show em but i must bring the rods and piston so i did, Then i ring him the next day and ask if he's had chance to show em? he says they said the same as him that the cars been detting i asked for him to show me the signs of detting No answer given ... ok what about the big ends they would show it for sure if it was that bad to wear the thrust.... still no answer... maybe the pistons hitting the head he says ERRRRR i feel an anger attack coming on lol. LOOK AT THE PISTON!!!!! Do you see any marks (APART from the turning marks!!!) on them to indicate they hit the head !!! ...no he answered! Then he trys to fob me off with the excuse that the pistons have scratched on the side skirt that means they over heated .... I dont think so i told him im not stupid them marks are marked due to the amount of metal floating about in the engine from the crank/thrust and that a piston that has got hot and picked up in the bore start at the bottom and fade out as they rise towards the crown not just ramdom scratches which some start half way up and may only be about 5mm long. So now its in the hands of the F.E.R who are going to inspect the crank and hopefully come back with an answer.

I just thought i would put some pics on here to see if others thought that these machine marks could do something like this or if anyone come up with another reason?

fujack

bttt

p1mark

In the last pic you posted:-

http://i67.photobucket.com/albums/h2...k/DSC_9122.jpg

i cant really see anything out of the ordinary. I'm still not certain you are not getting a little confused with original machining marks.

I'm not trying to be a smart ****, but i know a bit about crank manufacture and i'm not 100% certain on what you are suggesting. Could you photoshop a couple of arrows on the pic to the marks you are talking about?

p1mark

Its this qoute thats confusing me. Your regrind man will not have done anything down here, and even grinding swarf will not cause marks on a face that is not contacting or in friction with anything else. Hence my worry that you are looking at marks from the original Subaru machining.

Lateral Performance

iTrader: (20)

Mark,

The first picture seems to give a better idea of the re-grind. What do you think of this ?

p1mark

Yes i have seen that Mark, and its obviously not from the grind itself but from wear. It would be difficult to grind that if you tried.

All that wear and damage is Daimetral around the crank centre though, which is obviously what you expect. What i don't understand is the original poster talking about wear/marks/damage that are at a tangent to the CL, and the fact that he mentions the end next to the flywheel which has no thrust feature, only a turned oil collar and a Turn Broached / milled web face.

Looking at that picture alone (and the one of the thrust bearing) its a fair assumption that:-

A) something foreign has got between the thrust face on the crank and the thrust bearing.

B) The repair was U/S on the thrust width - assuming it's been metal sprayed or something, and / or the thrust bearing was O/S. I'm also assuming that whoever built it did not check for end float.

fujack

ok i have zoomed in so you can see where im on about a bit better .

http://i67.photobucket.com/albums/h2...thrustside.jpg

http://i67.photobucket.com/albums/h2...lywheelend.jpg

Lateral Performance

iTrader: (20)

Mark,

I must say I'm surprised you say that. I would have thought the bearing would have far more damage, given how much softer it is ?

Just wanted to say that I had no involvement in the engine parts, or build.

fujack

forgot to add thats the otherside of the thrust and these marks can be found on every face either side of the mains.

p1mark

Yes, they are just marks from the grinding wheel. They are not ground using the side of the wheel, but plunge ground. We manufacture cranks in exactly the same way. Its just the function of a dressed wheel with no side relief feeding down a face.

I will take a pic of a crank tommorrow, you will see what i mean. Totally normal. The geometry of the face will be fine. The other thrust face though is obviously damaged by something else other than a grinding wheel.

p1mark

Its not necesarily the case though mark. Crtanks are not particularly hard at all and the lead/bronze etc. alloys they use for bearings have good self lubricating properties while the steel crank does not.

You see the same phenomona on the pin and shell sometimes. You can get hardly damaged bearings (just slight scuffing) yet have a masively out of round pin.

Also think of old machine tools with cast iron beds and hardened steel slideways. The slideways wear first because of the high graphite (a good lubricant) content of the iron. Cast iron is really soft but is used because of its high lubricity.

p1mark

I have done my best with pics, unfortunately works digi camera is poo.

This is not a Subaru crank, but it's manufactured in an almost identical process (I have been to the Subaru Machine shop specifically to look at their crank/cam manufacturing m'c tools)

The first pic shows it best. The end journal is the thrust, there is about 5mm of thrust face and then outside of that is about 5mm of rough machined face.

If you look close you can see scratch marks running at a tangent to the crank centre. They are also there on the turn broached face, but obviously a lot more visible. These marks are purely a function of a grinding wheel or cutter plunging down a face.

On your subaru crank (as on the crank below) only the thrust faces are ground, all the other web and oil collar faces are rough machined. Hence the marks on all faces of your crank.
.



.

fujack

How comes i have another subaru crank from a friends engine and all faces are mirror shinny? Oh and also a subaru crank at the machine shop that did the work wainting to be ground

p1mark

Because there is a micro finishing op after nitriding that removes the white layer on the pins, mains and adjacent faces.

fujack

So how does that explain how my crank has marks on the thrust face and my friend dont as thay are both used cranks and all side faces are mirror smooth but mine are not?

fujack

The cranks now going off to be inspected by the FER so we will see what the out come is. Thing that gets me why do ppl grind cranks on subarus if they know it shouldn't be done or do they just wanna take your money?