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Crankshaft connecting rod wiggle play

Posted by John Mark Dongon, Mar 30, 2019

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  1. John Mark Dongon

    John Mark Dongon Proven Member

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    Ok so my mechanic was putting in my pistons today, and noticed one of the connecting rod caps had some side to side play. The rod cap would easily wiggle left and right with little force, hitting the side walls even after torquing (too much clearance) the other 3 rods was firm and wouldn't wiggle. He told me I would need a new crankshaft and didn't proceed to finish rebuilding my car. I've been reading around that its fine as long as there's no play up and down towards the journal. I know its best to get a new crankshaft but, i'm a cheap folk ok. What do you guys think is it safe? maxresdefault.jpg

    This isn't my picture btw just to give you guys an idea
     
    Last edited: Mar 30, 2019

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  2. DSMPT

    DSMPT Proven Member

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    That clearance is necessary for oil flow. And it's normal it moves side to side, but it depends how much clearance it has.
    Check the rod big end side clearance as below.
    0.1-0.25 mm (.0040-.0098")
    Limit: 0.4 mm (.0157")

    1.jpg
     

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  3. John Mark Dongon

    John Mark Dongon Proven Member

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    Ill go buy a gauge and check it out tomorrow, so if it exceeds 0.4 than the crank is bad?
     

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  4. DSMPT

    DSMPT Proven Member

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    Rod cap or crank, but to be honest you don't need to worry too much even if it exceeds a little bit the max limit.
    I would worry more if the clearance is tighter than the min limit.
     

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  5. motomattx

    motomattx Proven Member

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    Agreed with the above, the others need to have clearance, thats very important at this point, make sure that the others have at least the minimum clearance, your mechanic sounds like he doesnt know the basics of how an engine works, unless that rod has excessive clearance, but him saying the others are supposed to not move at all is very very wrong.
     

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  6. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    Here are the rod side clearances from my 2 recent 6 bolt builds as an example.
    It is what it is and I don't fudge my numbers on any build sheet.
    Rod side play, as long as it isn't EXCESSIVE (that is left up to each builder), doesn't worry me. Back in the day, we would hit the sides of a SBC or BBC's rod big ends with a grinder, just to let them live comfortably side by side and REV :shhh:.
    Same with cylinder wall clearance. I ran one SBC Corvette 327 with .011'+ in one cylinder and had a 150 shot of NO2 on it. Hell that thing would rev 8k all day long BUT it wasn't on a BOOSTED motor. That was back in 1984 or so, a few days ago. :)
    Just my .02 15539691716582651707120803455214.jpg 15539691912794153301404617055627.jpg
     

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  7. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    In case you want to see numbers to compair by....I have no secrets to hide. I didn't want to bore a block I could use. :)
    Wilson Engine Shop MW1 Spec Sheet  Final 3-22-2019.png
     

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  8. John Mark Dongon

    John Mark Dongon Proven Member

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    I found out that I had 1 bad journal. It seems to be smaller than the other 3 causing wiggle play on the connecting rod in between the bearings. Do you guys think its safe to run like this for right now, until I get a new crank, I dont mind any noises as long as it wont damage the block or pistons or rods itsellf
     

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  9. ThunderChild

    ThunderChild Supporting VIP

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    No, it is not ok to run with excess bearing play. Are you meaning rod side-to-side clearance or actual rod bearing clearance?
     

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  10. DSMPT

    DSMPT Proven Member

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    I don't know how bad the crank is. So maybe nothing would happen if short time, but you should wait until you get a good crank. I wouldn't take that risk. Worst-case scenario you would have is, a broken rod would destroy the block. In this case of course you would lose piston and more parts, too.
    Even nothing would happen, at least you would waste bearings.
     

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  11. ThunderChild

    ThunderChild Supporting VIP

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    I agree with @DSMPT , you should get a replacement crank and have all clearances set up correctly.
     

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  12. John Mark Dongon

    John Mark Dongon Proven Member

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    Ok so I took off my rods to check out the journals after turning the crank a few times and I noticed my new rod bearings got scoring lines on it! Is this normal 20190403_195835.jpg 20190403_195717.jpg
     

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  13. ThunderChild

    ThunderChild Supporting VIP

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    No, that's not good. There's debris in there. tear it back down, get a good crank, machine anything needed, clean the peewaddin' out of everything, and reassemble, check all clearances.

    You may also want new bearings. Also, are you rotating the engine over dry, with now assembly line or at least 30w oil??
     

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  14. John Mark Dongon

    John Mark Dongon Proven Member

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    Yeah I put some 30w oil on the bearings before installing, I just found out the journal has some scoring that caused the line but is very light scoring which is beyond me how it got those scratches with just a few crank turns
     

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  15. ThunderChild

    ThunderChild Supporting VIP

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    It doesn't take hardly anything to screw up the bearings, and 30w oilwill do for a couple rotations, but you really should be using some kind of assembly line that's heavier and will stick. 30w without pressure isn't going to stick much longer than a couple turns of the crank.
     

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