WBX-Unknown

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Re: WBX-Unknown

Postby multisi » 01 Jul 2018, 17:36

You said at the start that when a flywheel was put on it would only turn 355 degrees, wasn't that the reason you took it apart.
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Re: WBX-Unknown

Postby itchyfeet » 01 Jul 2018, 17:55

multisi wrote:You said at the start that when a flywheel was put on it would only turn 355 degrees, wasn't that the reason you took it apart.


that was the dizzy gear.
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Re: WBX-Unknown

Postby itchyfeet » 01 Jul 2018, 17:59

bigbadbob76 wrote:
itchyfeet wrote:My take on this is that all the machined surfaces may not all be square to the big and little end.


I agree there. I was trying to think through it, does it matter? my brain started to fry thinking in 3 dimensions at once.:lol:



No.
start with a lump of metal, cut one side, cut another keep going and they are all roughly square enough for the final cutting of the big and little end, who knows how they held it for that operation.

if I put two on a gudgeon pin and then slide them together onto a 3mm sheet spacer they bind up on the pin, this says the flat surfaces are not square to the little end but does not mean its bent.

I was surprised how much they flexed too.
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Re: WBX-Unknown

Postby bigbadbob76 » 01 Jul 2018, 19:59

fair enough, makes sense, so taking it a step further, would the side clearance beween the con rod and the crankshaft web then vary as you rotate the shaft, and would it show up with a feeler gauge?
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Re: WBX-Unknown

Postby 937carrera » 02 Jul 2018, 08:42

Most OEM conrods are drop forged, so stamped and then machined, rather than machined only rod and cap being done seperately.

Some newer conrods are made as a one piece, with a break line and the cap is then snapped off. No smooth line, caps only fit the rod they were broken from. I haven't really come to terms with that development yet, they look wrong. :)

Thanks for slotting the rods on the pins Paul, I wasn't sure what you were thinking before and thought if I measure on the pin that I would also be measuring small end wear, rather than the rod only. There is no reason why the sides of the little end have to be at 90 degrees to the pin, indeed if you pile all 4 on top of each other and press the little ends together you see that they fan out. On the other hand, having it a little wider at the base of the pin provides additional strength for the compression stroke. The big ends are I think at 90 degrees, but will check.

I started to strip down the engine because it wouldn't turn over. With one head off it did turn over. The conclusion is that it was the dizzy drive, but either way unless the engine turned over smoothly, endfloat was good and it gave good leak test results it was always going to be stripped for further inspection.

I haven't been with the engine for a few days so no more "news". I'll have another look and measure and then decide what route to take. Part of me is thinking, I'll take them along to the engineer, just so I can see what he concludes and how that matches up with my measurements, part of me is thinking, if I'm going to rebuild the engine I'm into buying new bolts anyway so the cost of new rods is less than it looks

Want to know a bit more about rod manufacturing ?
https://www.forging.org/uploaded/content/members/field_document/A_Comparison_of_Manufacturing_Technologies_in_the_Connecting_Rod_Industry.pdf
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Re: WBX-Unknown

Postby itchyfeet » 02 Jul 2018, 08:58

If you buy new rods how do you know one is not bent?
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Re: WBX-Unknown

Postby 937carrera » 02 Jul 2018, 09:23

I would proceed in blissful ignorance :lol:

Mahle quality assurance procedures must count for something, the reason I checked these rods is really only because of the wear on number 3 shell.

Having an unknown engine is a matter of being a bit of an engineering detective. I still have piston & barrel condition for 2-4 to check
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Re: WBX-Unknown

Postby itchyfeet » 02 Jul 2018, 09:33

doesn't matter how tyey left the factory its whats happened to then since
they may have been made 20 years ago and been shipped to the other side of the world and back
Stacked under 1000 other rod sets or dropped.
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Re: WBX-Unknown

Postby bigbadbob76 » 02 Jul 2018, 10:08

937carrera wrote:I would proceed in blissful ignorance :lol:


:rofl :rofl :rofl me too.
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Re: WBX-Unknown

Postby 937carrera » 02 Jul 2018, 10:12

Insufficient force to do that, IMHO

As I don't know the forces involved, rather than rely on instinctive engineering I went on a quick google and came across this

Funny as I know a Neil Harvey that does Porsches, looks like he has a namesake in the US too

Okay SoobyDoo fans, I have a bit of a mystery. According to Neil Harvey, one of my connecting rods was bent: out of true by .060 when it was checked for straightness. There was no piston damage, no signs of detonation, no valve impressions on the piston crown, no valve damage, the wrist pins didn't look worn, no broken circ. clips, the crank was fine, and the cylinder bores didn't look funky. I know these aren't Carrillo or Pauter rods, but they aren't made of chocolate either. According to Neil it takes a great deal of force to bend a rod like this...even an OEM one. Now granted I didn't send Neil my old Ps&Cs because I bought brand new ones, so I'm only able to give them a visual inspection...I don't have all those fancy bore gauges. What could cause this? I asked Neil if there was a possibility that the rod was bent when the engine was assembled by Porsche (a defect) and he said that yes it was possible...anything is! You know, built on Friday during Oktoberfest! I don't have a picture yet, but that's been the hold up! Neil has been trying to find a rod that was in the right weight group as the other five...HE FINALLY GOT ONE! When I get the bent one back, I'll snap some pics of it. In the mean time, does anyone have ideas? It would have to be one hell of an explosion in the combustion chamber to bend a rod like this, and then I'd expect to see other damage...



I also asked Neil about the possibility of the rod being bent during shipment from NC to CA. He said that it wasn't possible. That I could stand at one end of his shop and throw the rod as hard as I could against the wall at the other end of his shop and the rod would not sustain damage of this sort.


and

I also discovered a bent rod during a rebuild. After some investigation I learned the engine had dropped a valve and had a piston, cylinder and head replaced. I guess the mechanic doing the repairs didn’t see the rod. When I say bent I mean the rod was twisted. The machinist caught it when he was doing the wrist pin bushings. The engine ran for 30k miles like that with no damage to the new cylinder and piston and didn’t make any unusual noises.


Con rod bending generally only happens due to hydraulic lock, always possible with WBX engines.

Full thread here
https://rennlist.com/forums/911-turbo-930-forum/257442-the-mystery-of-the-bent-connecting-rod.html
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Re: WBX-Unknown

Postby itchyfeet » 02 Jul 2018, 11:56

937carrera wrote:
Con rod bending generally only happens due to hydraulic lock, always possible with WBX engines.


fom what? coolant leak or oil?

this was a repaired engine is it possible VW didn't replace rods just refirbished them and this was damaged brefore?

I like the throwing a rod across the room as hard as you can statement, I dare you to try it to demonstrate your total belief in articles you find on the internet.. :rofl
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Re: WBX-Unknown

Postby 937carrera » 02 Jul 2018, 12:23

Usually coolant leak from head gasket or from splitting the bore / liner, it needs to be a either sudden inundation when running or a build up when engine stationary that then locks when starting. Filling with oil is referenced in that Rennlist thread, but I hadn't heard of that before.

I'm not going to throw one of my rods across the room, I don't want to damage the breeze-block :rofl

I am on the page that the engine has been rebuilt with a bent rod. Not necessarily by VW as it could have been rebuilt by them once, and then again by someone else. Did I mention this engines history is unknown. :) As referenced in the Rennlist thread and quoted above, someone else found a bent rod on a rebuilt engine when rebuilding it again. Better quality builder second time around in that case by the looks of things.
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Re: WBX-Unknown

Postby bigbadbob76 » 02 Jul 2018, 14:41

937carrera wrote:Con rod bending generally only happens due to hydraulic lock, always possible with WBX engines.


Or someone using easy-start.... :run
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Re: WBX-Unknown

Postby 937carrera » 05 Jul 2018, 16:37

I managed to get a little time this afternoon fro some more con rod measuring. This time I simply used a sheet of paper as a protector between the small end faces.

One thing I spotted with fresh eyes is that the beam of the con rod is not eactly central in the rod, and the small end is not symetrical. In fact one side is 1.6mm wider than the other, when using the beam as a centre line. Here's a low tech annotation to show the situation, one one side the face of the small end is almost in line with the face of the big end.

The rule is there to emphasise the difference and show how close to parallel that side of the rod is

I didn't know that, I wonder why. I checked some other rods from a different engine and they were central, perhaps it's something to do with the torsional forces in a boxer engine :?: :?: :?:

It also demostrates why there is a right and wrong way up for the con rods

Image
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Re: WBX-Unknown

Postby itchyfeet » 05 Jul 2018, 16:48

I didn't know that.

Did you know pistons have steel in them?
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