zerocool

I rotated the first piston to BDC, removed the rod nuts, took out the old bearings, and put in the new ones. Following the instructions from Paragon and they say to place the plastigage on the journal. This may be a stupid question, but what or where is the journal? Also what should the plastigage read for everything to be OK? Thanks.

ribs

I believe the rod journal is what bolts around the rod bearings and the crank, and attaches to the rod (your rod bolts go through the bottom half of the rod journal, attached to the top half). The plasigauge should be the same girth as the replacement rod bearings (I think)...I did this procedure and didn't use plastigauge, using stock sized rod bearings, and everything seems to be working fine (as far as the bottom end is concerned), but if your rod bearings look scored to hell (check especially #2), you may need to have your crank machined and oversized rod bearings used. YMMV.

-ribs

Danno

" but what or where is the journal? Also what should the plastigage read for everything to be OK?"

Here's a picture of the rod-journals, it's the shiny round part that spins inside the bearings:


You want to replace the upper bearing with a new one, then lay a strip of plastigauge across the journal (shiny part where you see reflection of my finger). Place the other half of the new bearing into the rod end-cap and install it. Use the old rod-bolt nuts and tighten to spec. Don't spin the crank or wiggle the rod end-cap at all here or you'll smear the plastigauge, leading to false readings. After you've torqued the nuts to spec, remove them and measure how wide the plastigauge had been squashed. The Haynes manual says this clearance should be 0.0007-0.0027" (0.02-0.07mm). The wear limit is 0.0039" (0.10mm) at which time, you can use undersize bearings.

Clean off the plastiguage, then reinstall using new rod-bolt nuts with a little blue Loctite.

zerocool

Thanks for clearing that up Danno. I was getting freaked out because I was putting the plastigage in and then rotating the crank until the piston reached BDC again. After doing this, the plasitage was reading .7 mm. After doing it your way, the reading was a little under .05 mm

michaeldean

hen I rebuilt my last engine, I replaced the rod bearings as preventative maintenance - just as I'm doing this time with my 951.
Do I really need to use plastigage IF I take a micrometer and compare the thickness of the existing bearing shells to the new ones I bought (basically to make sure that the car does not have oversized bearing in it already).

I know there is some controversy surrounding the use of plastigage so I'd appreciate hearing a few perspectives on the subject.

Thanks!
Michael

emilysgranny

Michael;IMHO you can do it that way but it very easy to come up with a wrong number.If you have a ball micrometer you can measure it that way only as a rough comparison with any certainty.It will not give you the clearance you actually have.The best way is still the plastigage.That will give you a for sure reading if you follow Danno's instructions.HTH

Mark Parker

I agree heartily with Danno and Granny. If you measure the thickness of the bearing shells, you still know nothing about oil clearance, and that's what's really important. Plastigage is just too easy and way accurate. <img src="graemlins/wave.gif" border="0" alt="[byebye]" />