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Engine Building: Huge Crank Resistance With Only 2 Pistons

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Best Answer Moshtaraq , 08 April 2021 - 12:20 PM

To answer this thread: I took it to the machine shop for a linebore and now it runs like a clock!

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#1 Moshtaraq

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Posted 09 March 2020 - 11:42 PM

Hi again,

 

I'm building my first engine, I'm taking it slow and making sure everything is within spec.

I installed the crankshaft with standard bearings after checking the clearance. First I used normal motor oil and the crank moved freely and spun a bit on it's own after letting it go.

Then I wiped everything down and used assembly lube to do the final installation and it was a lot harder to turn the crank.

With 1 piston in, the crank had a lot of resistance (20Nm with my torque wrench). With 2 pistons it's gotten realy hard to turn the crank, even with a normal ratchet.

I checked the clearence of the big ends and mains as well as the end float and all were in spec...

Is this normal? Opinions seem to differ on what resistance is acceptable. But this resistance seems a bit much and I'm doubting the engine would produce enough torque to turn the engine :lol:

 

Any advice is welcome!



#2 DeadSquare

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Posted 09 March 2020 - 11:50 PM

Did you oil the bores ?

 

Slack the big end bolts a little and see if it alters the resistance.



#3 Moshtaraq

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Posted 09 March 2020 - 11:55 PM

I put a good amount of assembly lube on the bores. Should I just use oil instead of that thick lube?

Loosening the big ends a bit doesnt do anything, only when I completely loosen them, the resistance is gone.



#4 DeadSquare

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Posted 10 March 2020 - 12:11 AM

Until I got a can of "Bardahl" (google it), I always used EP90 gear oil when assembling the bearings,  and by filling the oil filter and priming the oil pump, (neither of which the factory did)  I never had any problems.

 

Try very carefully wiping the bearings and bores and re building with oil.  This will at least tell you if it is the assembly lube or something serious.



#5 Tupers

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Posted 10 March 2020 - 12:13 AM

You don’t want assembly lube on the pistons or bores just a light coating of fresh engine oil.

Make sure you’re putting the pistons in the correct bores and the connecting rods are in the correct orientation. I’m my experience with all 4 pistons fitted you should be able to rotate the crankshaft with a firm grip on the cranks tail.

Edited by Tupers, 10 March 2020 - 12:14 AM.


#6 Moshtaraq

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Posted 10 March 2020 - 12:14 AM

I will try that in the morning. I'm really hoping it's a lubrication issue and not some bearing misallignement cause I'm capable to fix that myself...

#7 DeadSquare

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Posted 10 March 2020 - 12:15 AM

I will try that in the morning. I'm really hoping it's a lubrication issue and not some bearing misallignement cause I'm capable to fix that myself...

Sleep well.



#8 Moshtaraq

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Posted 10 March 2020 - 12:16 AM

You don’t want assembly lube on the pistons or bores just a light coating of fresh engine oil.

The piston bores are coated with engine oil, the bearing surfaces with the thick lube. I followed the haynes manual for the piston orientation so I don't think that could be the issue.

#9 Tupers

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Posted 10 March 2020 - 12:17 AM

What work has the engine had done?

New pistons and a rebore, reground crankshaft or are you just cleaning it and reassembling with new bearings?

#10 Moshtaraq

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Posted 10 March 2020 - 12:19 AM

The engine has been bored +60 and honed. New high compression pistons with new rings, new bearings.

#11 Tupers

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Posted 10 March 2020 - 12:26 AM

Have the piston rings been gapped correctly and did you test fit the pistons without the rings?

#12 Moshtaraq

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Posted 10 March 2020 - 12:28 AM

Good point, I forgot to gap them. Missed it on my to do list.... The pistons without rings fit nicely though.

#13 timmy850

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Posted 10 March 2020 - 02:04 AM

Have you got the bearing caps on the right way? The retaining tangs should be on the same side

And as mentioned above are the conrods in the correct order? They are offset different directions depending on the cylinder

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#14 Earwax

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Posted 10 March 2020 - 04:38 AM

Lots of good advice.  If in doubt I would go back to the beginning.Take it all apart.  Put block caps in (oil on crank side only) and sit the crank on it. Spin away to get the feel. Then start with centre cap main, make sure the dowels pop into place. Bearing tang to tang, oil on crank side only. Nip it up to tight but not torque setting and spin away.... still free, back off the bolts and then torque up to spec on centre only. Spin away.  Add the front and rear caps in a similar way and guess what,,,, don't forget to spin away. Once bare crank is in, you will know whether you have some crud on a bearing, or at least if any end is nipping up.Crank only is still hand spin and some run on, once you systematically add the ringed pistons some load develops. I have heard of cranks tightening up when added to some engine lubes rather than just plain old oil, but i haven't used anything but oil , so couldn't say.



#15 Moshtaraq

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Posted 10 March 2020 - 06:34 AM

Lots of great advice, thanks!
Will look into it today and report back.
Love this community





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