Wayne - Replacing Rod Bearings?

[Andras]

As a follow up to Wayne's suggestion to replace the rod bearings in my 911SC engine, can this be done without splitting the case?

Can the rod bearings be replaced by going through the opposing cylinder holes, working our way through all six?

It also seems that one can get access to the crank through the sump plate, though only on cylinders 2 and/or 5.

[911pcars]

You can access all the rod bolt fasteners by removing the pistons and cylinders. Don't drop the nuts into engine.

Sherwood

[Superman]

Yes you can, but:

1. Splitting the case is fun and easy and

2. The most wear you will find will be on the intermediate shaft bearings and on the main bearing that's next to the flywheel. Those are inaccessible except by splitting the case.

If you do not split the case, you'll probably feel mostly comfortable that you made the right choice, but you'll be nagged by the suspicion that you should have done it. If you do split the case, you'll be glad you did when you see those old bearings. Also, this allows you to renew both timing chains with non-masterlink units.

[KobaltBlau]

Superman, what condition did you find your intermediate shaft bearings in when you split your case? I read the thread where you were agnonizing about it, but never found the result.

TIA

[emcon5]

What Jim said. My mains looked great, my layshaft bearings were shot, at 112K miles

Tom

[john walker's workshop]

you place the rod cap with bearing and bolts onto the journal and then rotate it 180° so the bolts face outward. stick a long screwdriver thru from the other side to hold the cap in place as you slip the rod onto the bolts.

[Henry Schmidt]

When assembling a crank and rods I always measure the crank for proper clearance. What I have found over the years is that crankshafts don't ware perfectly round. They tend to ware flat on the top and bottom of the journal. Oval like or egg shaped. It has been my experience that measuring a rod journal through the piston spigot is pretty hard. It is also a great feeling when after assembling a crank with rods that you can spin the rod all the way around to feel for side play and tight spots during a full revolution. This case together short cut seems to fit the " not enough time to do right, plenty of time to do it over" category.
PS: Even the best machinist make errors.

[Superman]

My layshaft bearings were showing copper. Sure, they'd have survived for many years and miles, but they were indeed worn. So was the rear main bearing, which also had a bunch of captured junk imbedded in it.

Splitting the case and replacing all those bearings was about the easiest part of the rebuild. The closer you get to the center of the engine, the simpler it is. Most of the complex stuff is bolted to the OUTSIDE of the engine. When all that complicated stuff is removed, the next most complex part is the heads, cams, chains. Then P&Cs, rings, wrist pins, etc.

Once you're down to the case, it's just a few nuts and bolts and Voila! You're looking at a crankshaft, an oil pump and a layshaft. That's it.

[Wayne 962]

Henry makes A-1 excellent arguments here. If I remember correctly, this was a low-mileage motor with broken rings (probably from detonation / ignition problem?). If you're trying to do it right, then yes, tear down the bottom too. However, you could get away with just a top end. Another thing - you could open up the rod bearing and measure/inspect them. If they are in spec, then you don't need to replace them (just use new rod bolts).

-Wayne