connecting rod clearance question...
Posted by Mad Matt F
Mad Matt F Matt Follett Elite Moderator Location: La Belle Province, Montreal Join Date: 03/13/2006 Age: Midlife Crisis Posts: 645 Rally Car: Don't Laugh, the Justy is Fun! |
So...
In yet another attempt to put Justy back together again... I am wishing I hadda built da volvo... With low oil pressure and a slight rod knock durning our awesome 2 stages last year... a few weeks ago I finally had time to pull the pan. #1 connecting rod bearing's shot. This is a typical weak point in the motor. The oil pump is junk, and wears quickly. When it does, it lets the connecting rods know. We were running low 20lbs of pressure, dropped to 10 as the knock got worse. long back story, but the current crank in there only has maybe 20 hrs of run time after a re-grind, and that was a new bearing (25 over). Mains are all good, the other connecting rods not bad. Here's the question. #1 Journal measures 41.59 mm one way, 41.78 the other... is that too out of round to bother trying to put new bearings in? it looks and feels smooth... maybe the grind wasn't real accurate, I don't know what tolerances should be... Pines this year is slipping from my grasp again... Thanks |
john vanlandingham John Vanlandingham Infallible Moderator Location: Ford Asylum, Sleezattle, WA Join Date: 12/20/2005 Age: Fossilized Posts: 14,152 Rally Car: Saab 96 V4 |
That journal is pounded, 0,2mm is .008". Clearance should be .0015" to .002" As vital to check is the size and roundness of the rod big end ID---which some suggest is perhaps the single most critical dimension in the motor, and if the bearing was pounded thing--measure it--compare against sumpin that looks OK, but if its pounded, then the rod needs a rebuild or a fresher, virgin-er rod swapped in... Didya consider adding a skinny washer under the relief valve spring to bump the oel druck ein bissschen hocher? Izat thing an aluminum block? Whaddya have for oel kuhler, junge? See alloy blocks GROW more than ol iron junk, and as the grow, oil pressure mysteriously disappears.. Better call, too much typee typee. John Vanlandingham Sleezattle, WA, USA Vive le Prole-le-ralliat www.rallyrace.net/jvab CALL +1 206 431-9696 Remember! Pacific Standard Time is 3 hours behind Eastern Standard Time. |
Robert Culbertson Out of this dumpster fire Professional Moderator Join Date: 08/15/2010 Posts: 1,236 |
0.20mm converts to about 0.008in. That is really out of round for a rod journal. I wouldn't worry if it was 0.002in/0.05mm. But that is way too much. The bearing clearence is usually around 0.003in/0.08mm. Not a whole lot of space in there for dirt and egg shapped journals.
Edit: And John beats be to it! Definietly check the big end of the rod as well as the crank. I have had 2 VW motors where the big ends were so deformed that when when assembled, you couldn't rotate the engine. Reconditioned rods are cheap, new rods shouldn't be much more. Edited 1 time(s). Last edit at 10/25/2012 09:12PM by Robert Culbertson. |
john vanlandingham John Vanlandingham Infallible Moderator Location: Ford Asylum, Sleezattle, WA Join Date: 12/20/2005 Age: Fossilized Posts: 14,152 Rally Car: Saab 96 V4 |
On real race motors with real oil pumps and real temp control yeah.. And 002" outta round OK? Yikes! Matt send me you fawking 514 numba John Vanlandingham Sleezattle, WA, USA Vive le Prole-le-ralliat www.rallyrace.net/jvab CALL +1 206 431-9696 Remember! Pacific Standard Time is 3 hours behind Eastern Standard Time. |
Mad Matt F Matt Follett Elite Moderator Location: La Belle Province, Montreal Join Date: 03/13/2006 Age: Midlife Crisis Posts: 645 Rally Car: Don't Laugh, the Justy is Fun! |
Argh... that's what me thought.
K well first off, its nighty night time soon. John I'll give ya ring tomorrow maybe. Alloo-min-ee-um? Boo whaa ha ha. No twice recycled WWII destroyer anchors... Oil filter spin on oil cooler adapter thingy procured. Oil cooler from jy found. Didn't run one before. And you need tight enough clearances for the spring under the relief to work silly! Will a wad of chewing gum.on the journal work? Matt |
john vanlandingham John Vanlandingham Infallible Moderator Location: Ford Asylum, Sleezattle, WA Join Date: 12/20/2005 Age: Fossilized Posts: 14,152 Rally Car: Saab 96 V4 |
My dear departed Dad said back in the war (the last one that we fought because we had to, WWII) he was North of Phoenix AZ doing bombing training for a few months so he and some friends bought an ol Chevy for $125 and would pile in and drive into town...It may not have had a real oil pump and the thing rattled out the bearings so they pulled the pan, and snipped up some handy beer cans they found (and drained), snipped them up into strips, wound them around the journals and hammered the caps on, and snugged them up. And drove it.. When it got too noisy, they repeat. Lasted the 4-5 months they were there and they passed it on the the newbs who arrived. I suggest you do a little better. John Vanlandingham Sleezattle, WA, USA Vive le Prole-le-ralliat www.rallyrace.net/jvab CALL +1 206 431-9696 Remember! Pacific Standard Time is 3 hours behind Eastern Standard Time. |
Mad Matt F Matt Follett Elite Moderator Location: La Belle Province, Montreal Join Date: 03/13/2006 Age: Midlife Crisis Posts: 645 Rally Car: Don't Laugh, the Justy is Fun! |
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Mad Matt F Matt Follett Elite Moderator Location: La Belle Province, Montreal Join Date: 03/13/2006 Age: Midlife Crisis Posts: 645 Rally Car: Don't Laugh, the Justy is Fun! |
okay...
So here's to percision instruments. I was a bit dismayed at the amount of out of round, particularily with the recent grind, and the fact it didn't look "too bad" So I tested my borrowed metric digital calipers on my glass desk top. 8.10mm 8.06mm 8.00mm 8.04mm So yeah. I bought a micrometer today. Journal dimensions are: 1.6401", 41.6585 mm one way 1.6426", 41.7220 mm the other... Do I still need the tin snips and beer cans? That's .0025" out of round. The stock crank spec (from Rockauto...) is 41.9887 mm to 41.9963 mm 1.6531" to 1.6535" the current bearing in there were/are .25 over, I assume that's mm... so does that mean the journal should be 41.7387 to 41.7463, in which case I'm done anyway... Thanks. Matt |
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