Big end bearings

[Paulstewart20]

Hello, My 172 after a track day decided to make a tapping noise so quickly shut it off and diagnosed big end bearings, so i removed the sump found one had become worn and loose. so being as this engine only needs to survive one or two more track days i decided to replace the bearing and not worry about the crankshaft. so bearings changed and torqued to 20nm plus 40 degrees. So now the engine wont start just one click and thats it, Battery is good, tried to spin the crank but the nut just loosens or tightens.
Engine ran before so i know its not seized.
Im guessing either
1. torqued nut is too tight and wont let crank spin.
2. starter is the issue somehow?

Open to ideas before i strip it down again tonight

 

[william84]

Might have metal build up on crank wet n dry it see if it helps

 

[bloke]

Rod will be out, guessing it was blue?

 

[Paulstewart20]

What do mean?

 

[bob the builder]

oil pump failure, no 3 and 4 main bearings will probably of picked up on the crank, did you check all big end bearings ?

 

[Paulstewart20]

I took it apart chain is good the cogs inside at the bottom would good the filter was not blocked, so how can you tell if oil pump caused that? Yes changed all bearings all good apart from one

 

[bloke]

bearing spins and overheats the rod, bottom of it will of been blue and it distorts it so when you stick new shells in and tighten the cap it locks the crank.

 

[Paulstewart20]

No it looks fine, I know what you mean on another engine had the rod snap and the crank when a dark colour then but yeah crank on this one looks good,any tips for the oil pump it looks good to my un trained eye but anything I can do to test it?

 

[bloke]

no blue on the rod?

 

[bob the builder]

if there is no blueing and the other bearings were ok then prob not pump failure

 

[Paulstewart20]

Ok so when I loosen off the bearing and tighten the nut just before 20nm I get maybe half a turn and then the engine locks, does that mean crank has warped or rod can this be fixed in situ? This only needs to do one or two track days then it's got a new engine going back in over the winter, are there any short term tricks?

 

[bloke]

will be rod at least, no chance of it running and doing a track day!!! you're pissing in the wind.

 

[Paulstewart20]

Lol fair enough, time to start my new build then or find another temp engine.

 

[bloke]

If I rebuild one that's span a bearing even if the rod looks fine it always goes in the scrap.

 

[bob the builder]

yep same here, never reuse a rod that has spun. just asking for trouble.