tight bottom end

[markey b]

random one as usual,

have rebuilt bottom end on the f7, but its very tight, required alot of force to turn over but will do smoothly once its 'spinning'

i had to use a huge bar to turn it over, its really tight, only replaced the big end shells, couple of piston rings and thrust washers and the part numbers are exactly the same on all the bits i've used, all parts have been genuine renault.

anyone else had this? maybe it just needs a 'tow start' lol

[Bruce - BHPerformance]

If the tolerances on the new bearings are a bit tight or the crank is ovalled it will be tight till it overcomes that high point.

I once rebuilt a 5 engine and had to mix and move the bearings about between cyinders 3 times until the crank ran freely.

Didn't have any plastigauge to check the tolerances at the time.

Take off the big ends and try the crank without them, if it spins freely then its time to reinstate the big ends torqued down one at a time till you find the tight one.

[Scoff]

As bruce says you want to undo the b/ends and see if the crank turns nice. it should be very easy to turn over with no resistance.

Set the engine close to tdc so the pistons arn't travelling up/down the bores when you rock the crank back and forth. Connect each b/end at a time until you find the offending one. You might just have something caught between the bearing and rod or cap. If an engine needs a bar to turn it then it won't last 5 minutes !!

[5teve L]

Did you put the caps back onto the same rods? Also have you got it built up, head on etc, if it's got good comp it will be hard to turn on the compression stroke, mine is.
If it's just bottom end then it shouldn't be that tight.

[markey b]

crank span freely with no mains on, also span ok before they were torqued

definately no crap in beween them, may have mixed the caps up though :(

[TNT ANDY]

crank span freely with no mains on, also span ok before they were torqued

definately no crap in beween them, may have mixed the caps up though :(

Find out which piston assembly is causing the problem and them change its position and see it is still doing the same in its new location. If it is, put it back to where it came from. Now change over big end bearings from one that you know runs ok. If the same piston assembly binds again then the rod is must likely distorted.

I had the same problem with my C1J when rebuilt. It ran for years, but when I stripped it down after my Snetterton incident 1 bearing was squashed out of shape.

Hope this helps.

[djinuk]

laxative :cool:

[michael tierney]

slacken everything off....then torque up 1 at a time and keep turning.....also keep in mind that u may have something silly like a out of line crank(whip):)

[Ashy]

Didn't have any plastigauge to check the tolerances at the time.


Where do you find out what the tollerance should be?

[markey b]

it turned out that it was my fault...

c1j flywheel bolts are too long for an F7 crank... they were hitting the big ends!