Oversize bearings
08-20-2007, 01:22 PM
#1
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Oversize bearings
Hello, I took my block and crank to the machine shop awhile ago, and the other day they told me the block is fine, but I will need 50mm oversize rod bearings, and 25mm oversize main bearings if they grind my crank (I spun a rod bearing). They said they are having a hard time finding the correct bearings. I checked on pelican parts and they didn't have the sizes. Where else should I be looking? And are there any drawbacks of oversized bearings performance/reliability wise, or should I just go ahead and look for a new crank? Thanks in advance.
08-20-2007, 02:39 PM
#2
Im suprised no one has answered you yet.
I cannot find any main bearings but you can get the rod bearings in those sizes which from your post says thats all you really need. It would seem that if you simply spun a rod, you would just replace the mains with a standard size. Or do they have to turn both? If in that case, call Dave at lindseyracing and ask him. Hes a cool guy and will answer those questions for ya. Good Luck!
Heres a link to the bearings. http://www.lindseyracing.com/mm5/mer...de=944BEARINGS
I cannot find any main bearings but you can get the rod bearings in those sizes which from your post says thats all you really need. It would seem that if you simply spun a rod, you would just replace the mains with a standard size. Or do they have to turn both? If in that case, call Dave at lindseyracing and ask him. Hes a cool guy and will answer those questions for ya. Good Luck!
Heres a link to the bearings. http://www.lindseyracing.com/mm5/mer...de=944BEARINGS
08-20-2007, 02:55 PM
#3
Looks like I found you some .25mm main bearings. http://www.autopartswarehouse.com/pr...in_bearing_set
Looks like theyre in stock.
Looks like theyre in stock.
08-20-2007, 10:39 PM
#4
Drifting
oh this is good news! I had only found 0.25mm for my rebuild, and the shop thought they may have to weld the crank. 0.50mm (~20 thousands) could save the day!
08-20-2007, 11:06 PM
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Thanks 944-LT1! I'm going to go ahead and order those. Hopefully they will get the machine work done quickly so I can finish the rest of my rebuild, get it back in the car, and start her up!
BTW, should I get a set of new rods, or just replace the one that the bearing spun in? Also, any other things to do during the rebuild that would not be totally obvious to someone doing one for the first time?
BTW, should I get a set of new rods, or just replace the one that the bearing spun in? Also, any other things to do during the rebuild that would not be totally obvious to someone doing one for the first time?
08-21-2007, 04:58 AM
#6
Well, why did the bearing spin? Thats a loaded question. SPun bearings can be caused by alot of things. Mostly it is caused by metal-to-metal interaction becasue of lack of lubrication. Soooo, how are the oil passages in the crank and where you changing the oil? 60K is a very short time for Porsches engines. Where you racing it or taking a fast curve? What year engine is this?
When I rebuild, I make damn sure to check ALL clearances and I do this many times. Because your spun bearing was most likely caused by the infamous poor oil supply known on these engines, I would say just replace whats necessary and be done. But, I would check it all. So, hows the thrust bearing surface, camshaft journals, cylinder walls and piston skirts/rings, balance shaft journals and bushings? Most all of this would require a bore dial indicator and the FSM for the factory specs/clearances. The biggest thing to watch is the torque settings for the rods/mains/ and other related bolts/nuts. ITS REALLY CRITICAL HERE. The rotating assembly is not one to be hastly strewn together so get a torque wrench. ANd dont be like me and buy one in inch pounds just to run all the way back to sears to get foot pounds HAha.
Another thing to check is the spun rods bolts. Check and see if they stretched at all. You may not need to buy a rod. Using the bore dial indicator, you can check for the specs that the FSM calls for.
One thing to make sure and do is to thoroughly clean the crank once you get it back. In fact, the good shops will tell you that. You want to get all the machining lube off as well as run compressed air/brake cleaner through the oil passages. Trust you me, theres a chance thats a metal shaving gets into one and decides to 1. come out and into the bearing surface and 2. block oil flow. Either way very bad.
Always use an engine assembly lube. On initial start up (and if you cant prime the oil pump) you will be running "dry" until the pump can charge the system. However, the pump works like a torque converter meaning it needs to have oil in itself inorder to pressurize the system. Im not sure but if you have all the belts off (as I think you would), once you have the rotating assembly installed and the oil pan back on and filled with oil, i think you can prime the system by turning the oil pump. Maybe someone will chime in on how to prime the oil pump of a 944.
Thats it! Good Luck Bud! Drop me a PM when its running and tell me of any weird issues or hold-ups so I can scribble them in my notes.
When I rebuild, I make damn sure to check ALL clearances and I do this many times. Because your spun bearing was most likely caused by the infamous poor oil supply known on these engines, I would say just replace whats necessary and be done. But, I would check it all. So, hows the thrust bearing surface, camshaft journals, cylinder walls and piston skirts/rings, balance shaft journals and bushings? Most all of this would require a bore dial indicator and the FSM for the factory specs/clearances. The biggest thing to watch is the torque settings for the rods/mains/ and other related bolts/nuts. ITS REALLY CRITICAL HERE. The rotating assembly is not one to be hastly strewn together so get a torque wrench. ANd dont be like me and buy one in inch pounds just to run all the way back to sears to get foot pounds HAha.
Another thing to check is the spun rods bolts. Check and see if they stretched at all. You may not need to buy a rod. Using the bore dial indicator, you can check for the specs that the FSM calls for.
One thing to make sure and do is to thoroughly clean the crank once you get it back. In fact, the good shops will tell you that. You want to get all the machining lube off as well as run compressed air/brake cleaner through the oil passages. Trust you me, theres a chance thats a metal shaving gets into one and decides to 1. come out and into the bearing surface and 2. block oil flow. Either way very bad.
Always use an engine assembly lube. On initial start up (and if you cant prime the oil pump) you will be running "dry" until the pump can charge the system. However, the pump works like a torque converter meaning it needs to have oil in itself inorder to pressurize the system. Im not sure but if you have all the belts off (as I think you would), once you have the rotating assembly installed and the oil pan back on and filled with oil, i think you can prime the system by turning the oil pump. Maybe someone will chime in on how to prime the oil pump of a 944.
Thats it! Good Luck Bud! Drop me a PM when its running and tell me of any weird issues or hold-ups so I can scribble them in my notes.
