Rod Bearings

Superman · 01-24-2002, 10:11 AM

My heads are at JW's Workshop for freshening (we don't know what that means yet, but if the valves were not operating properly before, they're likely to perform better now). Folks say that valve jobs should also include new rod bearings, since the fresh heads can put more pressure on the bearings. In spite of apparently excellent oil pressure, I have been planning on replacing the rod bearings anyway.

I'll need to figure out what tool I need to reach in there. It sounds like an extra pair of hands are helpful, and I've got three small pairs of extra hands around the house to keep parts from dropping into the case. I am now wondering whether I should just slap them in there, or whether I should try and use Plastigage. I'd like to hear comments on this, since there may not be much room for me to play around with plastigage. I wonder if I can comfortably assume that new factory-sized bearing shells will not provide a clearance problem (too tight, for example). Can I just install them and not worry, or should I try to Plastigage them.

And should I have a close look at the rod big-end dimensions to determine roundness? Finally, can I re-use wrist pins and wrist pin bushings? I will not be re-using wrist pin circlips, of course.

Superman · 01-24-2002, 03:33 PM

Bump. Speak to me, oh wise and learned men (and ladies) of power. Share with me the secrets of bottom ends (keep it clean). Can I just slap new rod bearings in the car and assume they are not too tight? Or should the time-honored Plastigage ceremony be performed to ward off evil friction-spirits? And does this hold true if I have the rods reconditioned? And share with me the mysteries of wrist pin bushes (again, keep it clean).

pbs911 · pbs911's Garage

Quote:

Originally posted by Superman
Can I just slap new rod bearings in the car and assume they are not too tight?

SM, I haven't done this on a P-car motor, yet. However, it goes against all I know about other motors. Hopefully someone will speak up. Have you asked JW? I mean it is only a matter of time before he chimes in.

Doug Zielke · 01-24-2002, 04:16 PM

Jim,
While you're waiting for JW to answer, take a look at your Spec book, starting with pg. 25.
Then, break out your mics and calipers.

Superman · 01-24-2002, 08:18 PM

Good point, Doug. I will soon know whether there is room for me to stick my hands in there and use tools such as mics and stuff. And Plastigage. I guess I was asking whether there will be room. I have a problem with patience.

You know, I'm also waiting to hear from the Big Kahunas on matters like assembly lube and head stud thread lube. And I'm waiting for my garage to heat up a little so I can go out there. Bye.

RLJ · RLJ's Garage

Hi Jim, load the case in your other car and take it and the rods and new bearings to who ever, Tyson or John and get them to measure the crank and the rods. Put the new rod bearings in the rods with the old rod bolts and torque them and measure the hole, see if it matches the crank (Think aobut new ARP rod bolts too). Building a high performance motor in the garage is great but ya' gota get things measured somewhere and checking eveything with a micrometer is very importand. I have seen guys use a ball anvil micrometer and measure rod bearing shells to .ooo1 and mix and match to get nervana.

Randy Jones
1971 911

PS- The old guy who tought me to build "OFFY" motors used 50%STP and 50% moly grease mixture for cam break in and 50/50 mix of oil and STP for eveything else. He said that was the only thing STP was good for.

RoninLB · 01-24-2002, 09:18 PM

I used some grey stuff on rod bolts that came in a tube, forget what it was. Rod bolts usually get engine oil on my past rebuilds. How does crank journals look? Should be able to see if any wear or if some thing doesn't look perfect on journal. I had a pro look,line bore, and mic. entire eng so I just put rods together. Seems like you will be using stock rod bolts. If your finger nail can grab any thing on journal you may want to stop the install. I'll look to see if I still have that grey stuff in garage tomorrow. Inspect old bearings or take them to some one and keep track of what came from where. Keep bearings in sets, IMO. I keep bearing to cap and bearing to rod surfaces oil/what ever clean and dry for assembly. I think that is important, some what. Torque wrench extensions reduce the applied torque. I may figure about 5 lbs for 6in and 10in extensions. I would suggest a clear head for rod nut install, technique is important. IMO, stock rod bolts are unforgiving. I changed oil filter about 1 hour after getting it started to clean up what was used on install. I would change oil about 500 miles later. I'm not a pro, only a neurotic wrench. I won't forget to look for grey stuff.

5axis · 01-25-2002, 01:44 AM

I have seen guys use a ball anvil micrometer and measure rod bearing shells to .ooo1 and mix and match to get nervana.

Randy, here is a toolmaker tip. You do not need a ball mic. Take a 1/4 dowel pin, mic that and you should get a.250 minus .0001 or 2.
mic the dowel and bearing and do a little subtraction. Working in tenths (toolie speak) requires extreme cleanliness, thermal control,and a whole bunch of patients. When I have to hit a number I set a gage block stack and double check my mic's to the stack.

The only place most people see two tent(h)s is camping.

David 89 turbo cab

Thomas Owen · 01-25-2002, 04:53 AM

Super,
Most of the experience I have with top-end jobs usually has involved a simple inspection of one rod bearing. The way the bearing has worn will tell an experienced eye about the condition of the crank. In my opinion, and please do not slam me for this, but I think if you are so concerned that you may want to use plastigage and/or a mic, then you should split the case. If it was my engine, with 185k on it, I would split the case, mag and polish the crank, and install new bearings. Your added cost will be the crank work, main bearings, intermediate shaft bearing, and sealer. You are then able to replace and torque all the rod bolts the way they should be, and you will sleep well at night.
Good luck,

Roland Kunz · 01-25-2002, 06:54 AM

Hello

never changed the rod bearings on a short block.

The best tool would be long slick fingers

And the key to a good engine is messuring messuring ...

BTW when they are out have the brocne bushing for the piston pin renewed and checke them for distorsion.

And wreite down witch number was on wich cylinder and in wich direction the number showed.

Grüsse

Superman · 01-25-2002, 08:39 AM

Just from wiggling the rods back and forth, the rod bearings feel pretty tight. And there seems to be very little room for hands in there, even small hands. I appreciate everyone's comments.

FWIW, I am still thinking that I will not split this case. Now, I am even thinking I may leave the rod bearings alone.

I have at times planned to split the case. But the wisdom prevailing in my mind right now is the "Everything is almost certainly very fine there and disturbing it may be as unwise as it is wise." I have very excellent oil pressure. The engine is a 3-liter. I have every reason to suspect that a look in there would reveal that everything is in nearly new condition. I'm not kidding. If I were to go in there, it would be to get at the layshaft bearings.....which are not making noise anyway.

I do appreciate everyone's input, whether you agree with me or not, and I'll keep listening with an open mind.

DRD · 02:19 PM

Super, If it were me ,I would go ahead and split the case. You have went this far, so might as well finish the job. It would be a real bummer down the road, if you had to the job twice?
When building a engine, it is better to be safe than sorry. You are rebuilding the top end, that will be strong, and might start to put addition wear on the bottom end sooner?
The layshaft bearings also like to wear, you might not hear any noise, but the bearings could be on there way out.
Just my 1/2 cents
Darren

RoninLB · 01-25-2002, 12:51 PM

"layshaft brg" excellent point. My original crank and rod brg. were great at rebuild time, but the layshaft brg. showed noticable wear. Would not have been able to see this without disassembly. IMO, at 100,000 miles layshaft brg. are a weak area.

stormcrow · stormcrow's Garage

As long as the engine is out do it all. splitting the case is no major problem. Now if you want to remove the connecting rod before you split it, you can do it.

You will need a 13mm socket with an extension to reach the nut. The crankshaft needs to be tdc when you do this. Once the nuts are removed, the connecting rod will come off and the other half will stay on the shaft but you have to use one hand to pull the connecting rod, and the other hand to hold the other half with the bolts in it. Otherwise, it will rotate and the bolts will drop inside the case and you will have to fish for them.

The thing about working on the engine is to learn about it while you do it. I took about a year to do the engine rebuild. Marked all the parts with a vibro-etch and laid them all out. Never did a P-engine before although I had done several v-8, v-6, four cylinder rebuilds.

As I have stated in a previous post, the tolerances are a lot closer and I can see why. The engine is well balanced and since the rebuild, mine runs like a top.

Parts for my rebuild came to approximately $1,200.00. It is a great achievement to disassemble one of these engines and put it back together and have it run. It gave me great satisfaction and pleasure knowing that I could do it and do it right.

Steve

Jim T · 01-25-2002, 02:24 PM

Quote:

Originally posted by Superman

I have at times planned to split the case. But the wisdom prevailing in my mind right now is the "Everything is almost certainly very fine there and disturbing it may be as unwise as it is wise." I have very excellent oil pressure. The engine is a 3-liter. I have every reason to suspect that a look in there would reveal that everything is in nearly new condition. I'm not kidding. If I were to go in there, it would be to get at the layshaft bearings.....which are not making noise anyway.
.

Some Q's:

How could properly rebuilding the bottom end be unwise?!? I don't get that.

How many miles are on the engine, and what are your reasons for suspecting that EVERYTHING in the bottom end is "like new"? (An engine is only as strong as its weakest link). Do you have some specific reasons, or just hope?

I think people naturally fall into one of two camps: "Full rebuild" and "top end" types. I guess I am naturally just a "full rebuild" type person. Unless the bottom end had like 10,000 miles on it, I would just redo the whole thing while the engine is apart. It just feels good to me to have a fully rebuilt engine. Cleaned and micropolished crank, magnafluxed rods, all new bearings and seals, etc.

Unless the bottom end has really low miles, a half rebuild would always bug me. Esp. if the car is going to be a long termer.

Roland Kunz · 01-26-2002, 05:29 AM

Hello

Otherwise, it will rotate and the bolts will drop inside the case and you will have to fish for them

If this happens you better split the case.

The rod bolts are not supposed to be loose in the lower rod end.
You have to tap them slightly to come out if they will slip out the rodboltshank is streched or the rod bolt hole out off spec.

Soket size depends on the engine version.

Full or topendrebuild is a desicon based on how the engine did perform before and how the parts look.
however a full rebuild is better/safer but the 911 bottom end is just to overconstructet to get stressed by 100 000 mls.

Grüsse

Jcon · 01-26-2002, 06:55 AM

I am by far the least experienced of this group on P-Cars. I have rebuilt quite a few motorcycles in the past. I have never regreted going all the way into the case ( much easier on a bike motor), but I have been burned more than once when I didn't. Nothing worse tahn doing the job a second time because you didn't go into the bottom end.

Just my $.02 ( Overpriced at that)

Jeff C
81 SC