need heavy advice freaking new problem - Page 6

upallnight · #51 05-17-2014, 11:22 AM

Quote:

Originally Posted by bcredliner

I haven't rebuilt a BMW head though have others and have a couple of questions

Align boring is extremely accurate. Why can't existing caps be transferred to 'new' head?

If the torque is only 10lbs, why should there be concern about cracking caps when you remove them or a torque sequence when they are tightened back? Wouldn't hurt but why is it a necessity?

Because each head is a little different from the previous heads. Like fingerprints, no two heads are usually exactly alike.

You can align new or used caps to use with the head, but that another cost since now you need to mount the head and all the caps and use a tool to align bore. Cost is usually over $100+ depending on the machinist you take it too.

When removing the cam bearing caps loosen all the caps evenly at the same time, don't take off each cap separately since the cam is under pressure from some of the valve springs. I seen noobs break cams because they didn't loosen the cam bearing caps evenly to relieve the pressure from the valve springs.

When you go to install the cam you need to tighten all the cam bearing caps evenly at the same time for the same reason.

Sponsored Links

bcredliner · #52 05-17-2014, 12:32 PM

Quote:

Originally Posted by upallnight

Because each head is a little different from the previous heads. Like fingerprints, no two heads are usually exactly alike.

You can align new or used caps to use with the head, but that another cost since now you need to mount the head and all the caps and use a tool to align bore. Cost is usually over $100+ depending on the machinist you take it too.

When removing the cam bearing caps loosen all the caps evenly at the same time, don't take off each cap separately since the cam is under pressure from some of the valve springs. I seen noobs break cams because they didn't loosen the cam bearing caps evenly to relieve the pressure from the valve springs.

When you go to install the cam you need to tighten all the cam bearing caps evenly at the same time for the same reason.

You can tell I haven't even read about rebuilding a BMW head, now I'm
interested, though except in the early days, I have left the headwork to the performance experts.

I agree the heads when cast will have some variation but when they align bore they would have already surfaced the head to true it up. I would think that would make any critical surfaces the same. Since the valve spring pressure is not relieved that means there is no way to check if the cam rotates freely so that makes it critical to me to use the same caps. Regardless, I agree, using the same caps would assure any deviation is eliminated and that's what I would do naturally as a best practice, was just wondering why it is critical--thanks for info.

upallnight · #53 05-17-2014, 12:53 PM

That would be correct if they only used the same boring machine for all the heads but they don't.

admranger · #54 05-17-2014, 11:25 PM

Quote:

Originally Posted by bcredliner

If the torque is only 10lbs, why should there be concern about cracking caps when you remove them or a need a torque sequence when they are tightened? Wouldn't hurt but why is it a necessity?

You aren't worried about cracking the caps, you are worried about cracking a CAM!

Maybe it isn't a problem on our engines, but on the S50/52, you needed to do this carefully as the residual stress in the hydraulic lifters would be enough to crack a camshaft if things weren't done right. There was even a $$$$$$ fixture to hold the cams down while you undid the nuts. If you didn't have the fixture (no one did), then people learned to gently release the pressure on the cams by slowly taking the nuts off in deliberate manner.

OP -- get a 1/4 inch torque wrench (it'll read in Nm and inch-pounds). Multiply inch-pounds by 12 to get to ft-lbs. You don't want to use a torque wrench at the limits of its range if you can avoid it.

1iwilly · #55 05-18-2014, 07:54 AM

thanks the 3/8 torque wrench i have goes from 5 to 80 ft-lbs.

Quote:

Originally Posted by admranger

You aren't worried about cracking the caps, you are worried about cracking a CAM!

Maybe it isn't a problem on our engines, but on the S50/52, you needed to do this carefully as the residual stress in the hydraulic lifters would be enough to crack a camshaft if things weren't done right. There was even a $$$$$$ fixture to hold the cams down while you undid the nuts. If you didn't have the fixture (no one did), then people learned to gently release the pressure on the cams by slowly taking the nuts off in deliberate manner.

OP -- get a 1/4 inch torque wrench (it'll read in Nm and inch-pounds). Multiply inch-pounds by 12 to get to ft-lbs. You don't want to use a torque wrench at the limits of its range if you can avoid it.

bcredliner · #56 05-19-2014, 11:00 AM

Quote:

Originally Posted by upallnight

That would be correct if they only used the same boring machine for all the heads but they don't.

Got it. Example of me being in my own little world of one off rather than the big picture.

bcredliner · #57 05-19-2014, 12:05 PM

The following is a tech article from Pelican Parts detailing camshaft removal: Pelican Technical Article: BMW 3-Series E36 Camshaft Removal and Installation

Suggest you scroll down to view the video first.

1iwilly · #58 05-19-2014, 09:12 PM

well got all the tools needed my bmw repair cd came today scroll thru it no biggie.
just waiting for the use head to arrived. drain the oil today had coolant in it good amount.
left plug off to get it all out to the last drip.LOL once again thanks to all that replied