924Board.org

[Martijnus]

I'm rebuilding my engine and will be replacing the crank and conrod bearings.

The crankbearings come in undersizes... .25mm if i'm right.
I understand that I need to get my crankshaft machined to fit these bearings... The reason I'm replacing them is just to be sure... I don't know if my current bearings are worn or if the crankshaft is.

So... When I'm going to order my parts, i've got the choice between stock and undersize bearings..

Now I'm kinda confused... because I've never done this before. If I buy the stock bearings, it could be that the crankshaft is worn and I needed the undersized ones.

If I buy the undersized ones, I need machining for sure (which costs money and I'm trying to save a bit of money... but not if it's necessary).
I actually don't know what the machining costs are, but if I get the wrong bearings I'm screwed anyway.

Anyone ever replaced the bearings? Is there a reason NOT to machine the crankshaft (like, when it's machined, it's weaker or something?).

I've found some cheap (really cheap!) bearings on ebay which are undersized... but its the difference between 40$ and 150$ (for stock).

edit:
ow wait... the ebay ones are rod bearings...

but I'm still wondering what to order...
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[Lizard]

you should remove the crank first and measure to find out what you actually need, then order.
_________________
3 928s,

[endwrench]

Lizard is correct. If you are not having any oil pressure problems you crank may be OK but you wont know until you remove it and have it measured by a machinest. There is no down side (other than cost) to having the crank machined as long as it is done by a competent machinest with quality equipment. Around here we have very good crank grinder guy and it would cost in the neighborhood of $75. Make sure your machinest leaves the fillets as Porsche designed it. You'll need both undersize rod and main bearings.

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[Martijnus]

[Min]

[Raceboy]

Yes, first get bearings, then decide what to do. Either grind current crank or get other crankshaft that could accept standard bearings. It may cheaper and faster to get a crank that is like new.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

[Martijnus]

Min, the bearings are easy to get from germany and 10euro cheaper than stock (thats NOT the reason I want them ), so that won't be a problem.

I've been told that if I deliver the engine to the machiner (mate has worked there for a while), they machine the crank to a certain specification and then drill through the complete engine with the bearings mounted to get a high precision.

I think the smartest thing to do is to call the machining company to ask what to do, what they do, what the costs are and so on.

First: get the engine out and look for wear.
Second: ask the pro's what to do when wear is or isn't found.
Third: get the stuff.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[Min]

[Martijnus]