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Author Topic: Conrod movement? - what's acceptable?  (Read 202 times)
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lanciamad
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Marcus Robinson


« on: August 06, 2017, 02:10:16 PM »

Starting to think about doing an engine build, the proposed engine has had work done to it (so called) with oversize piston's fitted, but not high compression versions so it's been apart before and when bought was told that it had new bearing etc at the time...
I'm hoping to get stuck into it next week at some point and strip it all out, mostly due to surface rust and cleaning required from the time it's been stored in the shed and to see what's what.
Having dragged it out, it still turns over by hand, just, so a reasonable starting point but noticed, that there is sideways movement with the conrod's, some people say there shouldn't be any, some say it's normal to have some movement, but what is acceptable? and with the beta engine should there be movement side to side?
They are all, roughly the same in regards to what movement they produce, some pics, and I apologise for the somewhat shakey video, but demonstrates what movement it has...
IMG_8639 by Marcus Robinson, on Flickr

Also just having a quick gander I notice the bolts holding the main cap between 2 and 3 are different to the others, is this normal?
IMG_8641 by Marcus Robinson, on Flickr

IMG_8642 by Marcus Robinson, on Flickr

IMG_8640 by Marcus Robinson, on Flickr

https://www.flickr.com/photos/lanciamad/36357102356/in/album-72157683304788332/

Thanks, Marcus
« Last Edit: August 06, 2017, 02:11:59 PM by lanciamad » Logged

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peteracs
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« Reply #1 on: August 06, 2017, 02:22:44 PM »

Hi Marcus

The link goes to an 'unauthorised access' screen, do you need to give it permission for external viewing?

Peter
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lanciamad
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Marcus Robinson


« Reply #2 on: August 06, 2017, 02:54:02 PM »

Hi Peter,
Changed privacy settings, hopefully allows you to view video now
Thanks Marcus
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1982 - Lancia Beta HPE 2000ie - Track - http://www.betaboyz.myzen.co.uk/forum/index.php?topic=472.0
1988 - Lancia Delta HF Turbo - Sorn - http://www.lanciasport.com/forum/index.php?topic=2585.0
1989 - Lancia Delta 1300 LX - Sorn
1988 - BMW E30 325i - Track
2005 - Subaru Forester XT STI - Road
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« Reply #3 on: August 06, 2017, 05:09:14 PM »

Hi Marcus. I have a very similar video of my conrods doing exactly the same thing from when I took my engine apart. I didn't measure the amount of movement. I wasn't too worried about it to be honest. I figured that it would all true itself up during running and a certain amount of float shouldn't cause any harm. All of the force is in the other plane. I figured that there would be some thrust washers (like those found at the flywheel end of the crank shaft) if there wasn't supposed to be any float. Maybe that's incorrect, but it made sense to me.
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lanciamad
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Marcus Robinson


« Reply #4 on: August 06, 2017, 05:43:05 PM »

This is also my similar thinking, and given all four are of a similar manner, hoped that this is normal and hopefully not cause for concern. I know a few people have experience with there own builds, so it will be interesting to see what they make of it. As you say, I guess of most importance is the lack of any play in the up and down movement.
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1982 - Lancia Beta HPE 2000ie - Track - http://www.betaboyz.myzen.co.uk/forum/index.php?topic=472.0
1988 - Lancia Delta HF Turbo - Sorn - http://www.lanciasport.com/forum/index.php?topic=2585.0
1989 - Lancia Delta 1300 LX - Sorn
1988 - BMW E30 325i - Track
2005 - Subaru Forester XT STI - Road
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« Reply #5 on: August 06, 2017, 08:27:43 PM »

End float on con rods is of no concern. It's normal and the rods keep themselves straight during operation as it's the path of least resistance. They only want to go straight up and down and there are no side forces to discourage them to do otherwise.

Crankshaft end float is a different game altogether and you have specific end float half bearings behind the flywheel to keep this in check.

The big end float you have there is meant to be.
« Last Edit: August 06, 2017, 10:06:33 PM by squiglyzigly » Logged

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« Reply #6 on: August 06, 2017, 10:02:15 PM »

Forgot to mention the centre main bearing cap bolts. They look different because they are. The centre main bearing cap bolts are much longer for extra strength (they pull from deeper into the block) because there is more stress around the centre main crankshaft bearings. The centre bearings are also bigger to help. Block and crank flex will be greatest in the middle as you would expect.
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HFStuart
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« Reply #7 on: August 06, 2017, 11:17:17 PM »

Agree with the others that big end float of the sort you have there is not an issue  - the rod is free on the gudgeon pin and on the crank so some lateral movement is normal. The only thing to be wary of is if  the little end bush is worn but that's pretty rare and usually evident once you have the pistons off.

Be careful of the heads on the centre bearing cap bolts - the undersides of the ones I've taken out have a very sharp edge  - sharp enough to cut my thumb quite memorably.
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« Reply #8 on: August 07, 2017, 10:07:21 AM »

Hi Marcus

This is normal for both questions. It is time to read Guy Croft's books on strip assess/ measure and re-build.

Enjoy

Eric
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lanciamad
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Marcus Robinson


« Reply #9 on: August 07, 2017, 08:28:16 PM »

Thanks all Smiley I couldn't find an answer in the book at first glance, all going well I won't come across any main issues. Suppose I better get the socket set out!
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1982 - Lancia Beta HPE 2000ie - Track - http://www.betaboyz.myzen.co.uk/forum/index.php?topic=472.0
1988 - Lancia Delta HF Turbo - Sorn - http://www.lanciasport.com/forum/index.php?topic=2585.0
1989 - Lancia Delta 1300 LX - Sorn
1988 - BMW E30 325i - Track
2005 - Subaru Forester XT STI - Road
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