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Author: Subject: conrod alignment on crankshaft
bikecarbfred

posted on 22/10/17 at 03:12 PM Reply With Quote
conrod alignment on crankshaft

I've heard of complaints in regards to bottom end fail due to cheap arp bolts. However the main rebuttal to this is inproper engine build and I can see why as I am carrying out my first build.

I can see a problem where conrods are not aligned in their correct/central place on the crank

I can see where journal bearings do not accurately align with their opposite counterpart due to fraction of movement in the main bearing caps whilst installing.

Bearings in the conrod do not have a locating groove there fore could slightly slide a fraction when installing.
The problem with these bearings are this problem is hard to spot as the crank is surrounding this region.


I also have a question.

1) When securing the conrod to the crankshaft how do you know you have it dead on centre where it should be.
Is it wise to hand tight the conrods and then turn the engine over twice for the rod to force it's way to it's central place and then torque the bolts up to the required specification?

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daviep

posted on 22/10/17 at 07:46 PM Reply With Quote
What engine are you working on?

Traditionally caps are dowelled to ensure correct alignment, more modern engines may use "fracture split" conrods which are not dowelled as the fractured faces fit together perfectly ensuring precise alignment.

Cheers
Davie





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bikecarbfred

posted on 22/10/17 at 08:47 PM Reply With Quote
that's a very aggressive profile pic you have on there.

the engine is afh 1.4 16v

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britishtrident

posted on 22/10/17 at 09:10 PM Reply With Quote
Life is too short stop looking for problems that don't exist if big end bolts fail it is due to over revving or a seized bearing or over tightening or leaving them slack.





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snapper

posted on 23/10/17 at 05:45 AM Reply With Quote
When tightening rod caps a feeler gauge either side will help (but not completely) prevent the rod twisting as you apply the final torque to the bolts.





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perksy

posted on 23/10/17 at 01:31 PM Reply With Quote
Don't forget to build it up with Plastigauge to check clearances

DTI the crank to check end float

If somethings not right when building it all up it should be pretty obvious to be fair
Especially when turning it over by hand

Also if using ARP bolts double check to see if the cap need chamfering to suit the radius under the ARP bold head, Some do some don't

Use the ARP lube and follow the instructions to the letter...



[Edited on 23/10/17 by perksy]

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FuryRebuild

posted on 23/10/17 at 04:47 PM Reply With Quote
can I just raise a point of order m'lud. ARP are a brand of bolts, and are exceedingly good. There are lots of knock-off sat around there on auction sites, etc. and I only buy them from a supplier I can trust. If they're cheap, it's for a reason.

britishtrident is right - and also maybe counterfeit bolts that aren't up to scratch.





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bikecarbfred

posted on 23/10/17 at 07:44 PM Reply With Quote
quote:
Originally posted by perksy
Don't forget to build it up with Plastigauge to check clearances

DTI the crank to check end float



[Edited on 23/10/17 by perksy]


When you say Dial gauge the end of the crank. Do you mean to check the end play. How much movement left to right there is?

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mark chandler

posted on 23/10/17 at 08:37 PM Reply With Quote
Cheap and ARP do not belong in the same sentence! The forces trying the split big ends apart are, phenomenal on the overrun at high RPM cheap bolts may fail.
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snapper

posted on 23/10/17 at 09:51 PM Reply With Quote
quote:
Originally posted by FuryRebuild
can I just raise a point of order m'lud. ARP are a brand of bolts, and are exceedingly good. There are lots of knock-off sat around there on auction sites, etc. and I only buy them from a supplier I can trust. If they're cheap, it's for a reason.

britishtrident is right - and also maybe counterfeit bolts that aren't up to scratch.


Depending on application some ARP products need shortening to fit, mainly in blind hikes
Just saying





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Hornet

posted on 24/10/17 at 09:36 PM Reply With Quote
Big ends can move side to side on crankshaft by clearances set by manufacturer. You do not need to worry about it. just fit them with plastigauge and if happy with results fit ARP bolts to correct torque with supplied arp lube.
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perksy

posted on 25/10/17 at 03:46 PM Reply With Quote
quote:
Originally posted by bikecarbfred
quote:
Originally posted by perksy
Don't forget to build it up with Plastigauge to check clearances

DTI the crank to check end float



[Edited on 23/10/17 by perksy]


When you say Dial gauge the end of the crank. Do you mean to check the end play. How much movement left to right there is?





You set the DTI up on one of the crank webs and then check the endfloat (backwards & forwards) If its out you'll be changing the thrust washers
Follow the Haynes manual or similar and all should be revealed

Use a good quality torque wrench and set of feelers
Measure everything if you have the right equipment
Use plenty of assembly lube or similar
Personally I like cleaning all the threads out of the assembled parts and all the oilways in the engine etc
I like packing the oil pump with Vaseline

Most important is you take your time and everything is spotlessly clean

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