Crank slack after installing rods 1/2 a degree

[Caprimaniac]

Friends....

Need a tip here. Thrown together a used crank with new bearings on mains and rods. Re- ringed etc for a street car.
Haven’t had any troubles with the parts in the past; ran just fine when disassembled.
Quick rebuild, so no clearances measured...(shame on me)

X-cuse me for ignorance- long time since last assembled engine, and i might have been blind to this in the past.

When all rods have been installed, mains and rods all torqed to spec, I notice there is a slack when I turn the crank. About 1/2 degrer on the crank. I ser a slight movement of the rods lower endd sideways, but feel no moment og any piston durin the 1/2 degree crank movement.
IS THIS NORMAL?

(Or did i install wrong size rodbearings or too much clearance and need of a regrind?)

I stepped over to my buds engine and DID in fact find something of a slack like I saw on mine. So, I think I’m ok..

Lost one night sleep over this- don’t need another one. Waited 6 months to get this thrown together...

[Dan Timberlake]

Is the "slack" = no piston motion ?

If the piston in question is at TDC, then you may be looking at "dwell" when the piston moves very slow and even more briefly stops.
It is even more extreme at BDC.
As shown by the v(elocity) = 0 at the 0, 180 and 360° points in middle graph here -
https://x-engineer.org/wp-content/uploa ... -angle.jpg

It sounds like, at this level of assembly, it would not be too hard to plastigage all the rod and main bearings.
If it was me, spending the hour or so to complete the P-gage check would improve my quality of ZZZZZs for weeks to come.
Conversely, NOT checking the bearing clearance would haunt me consciously and subconsciously for a good chunk of the remaining 2020.

[Nut124]

What Dan says.

The crank turns easy at TDC/BDC but if there is slack when pistons are mid bore then something is not right. Plastigauge costs $3.

[Walter R. Malik]

Most commonly known as "clearance stack-up".

[modok]

You should have compared the bearing thickness, new vs old.

[falcongeorge]

It sounds like, at this level of assembly, it would not be too hard to plastigage all the rod and main bearings.
If it was me, spending the hour or so to complete the P-gage check would improve my quality of ZZZZZs for weeks to come.

At the risk of stating the obvious, this is precisely the purpose plasti-gauge was invented for, a situation where someone was doing a basic bottom end assembly, and for whatever reason, wasn't able or willing to measure bearing clearance with mic's and snap or bore gauges. While myself and others usually use it as a fail-safe doublecheck, this is exactly the situation it was originally intended for, I do not understand why someone wouldn't use it here.

[Baprace]

Friends....

Need a tip here. Thrown together a used crank with new bearings on mains and rods. Re- ringed etc for a street car.
Haven’t had any troubles with the parts in the past; ran just fine when disassembled.
Quick rebuild, so no clearances measured...(shame on me)

X-cuse me for ignorance- long time since last assembled engine, and i might have been blind to this in the past.

When all rods have been installed, mains and rods all torqed to spec, I notice there is a slack when I turn the crank. About 1/2 degrer on the crank. I ser a slight movement of the rods lower endd sideways, but feel no moment og any piston durin the 1/2 degree crank movement.
IS THIS NORMAL?

(Or did i install wrong size rodbearings or too much clearance and need of a regrind?)

I stepped over to my buds engine and DID in fact find something of a slack like I saw on mine. So, I think I’m ok..

Lost one night sleep over this- don’t need another one. Waited 6 months to get this thrown together...

Caprimaniac , what did you find in your slack issue ? Is it running yet ?

[DCal]

When using Plasti guage you should take up the rod side clearance with a feeler guage or you get a faulty reading.

[Sparksalot]

Another important point to achieve accurate results is the parts must be free of oil. The rod journal, ID and OD of the bearing shells and the rod bore must all be dry.

If they are not dry the test will show a smaller than real bearing clearance.