Stretched rods

drof351 · Post by **drof351** » Thu Mar 10, 2011 8:57 pm

Hi guys, Has anyone stretched rods on a 2001 wrx? If so what caused it?

littlewhiteute · Post by **littlewhiteute** » Fri Mar 11, 2011 5:53 pm

Stretched rods? By how much?

Generally, pistons will strike the head and the engine will stop.

Bent rods are caused from trying to make more power than the rods can handle.

drof351 · Post by **drof351** » Fri Mar 11, 2011 8:41 pm

Thanks for the reply, had the engine rebuilt, fitted je race forged pistons, line bored etc to suit forgies, race bearings, reused the rods, serviced heads etc, its running a vf34? turbo with an autronic computer. He had it dyno tuned but it has different diffs front and rear so they couldnt do a power run and to be safe only gave it 7 pound boost and really fuelly until the diffs were sorted. Never got around to it. About 11 months on It started with a little metallic tick a couple of weeks ago, now its sounds like a solid piston hitting head. Told its stretched rods no warranty don't bother bringing it down to have a listen. Is it common?

BBoypebs · Post by **BBoypebs** » Fri Mar 11, 2011 11:48 pm

Stretched rod ??? Never heard of a stretched rod before.
seen plenty of bent and broken rodes.
It would be more likely a spun / failed bearing or the end cap has come loose.
may also be piston slap.

YouTube · Post by **El_Freddo** » Sat Mar 12, 2011 1:40 am

drof351 wrote:reused the rods,

Conrods or connecting rods - the part between the piston head and the crankshaft.

Reusing conrods on a performance engine is generally not a good idea unless you know the history of the engine - ie: it hasn't been flogged hard or at all.

The conrods hold the big end bearings that are the culprits for the knocking sound that you hear. The conrods may have been fatigued before you re-used them, while they may have appeared within spec during the rebuild they may have been already starting to stretch - this occurs from hard revving or over-revving the engine consistently and/or having poor oil pressure/not enough oil in the engine.

Unfortunately this part is reused and not covered by a warranty from what I can read from what you've said.

If you're mechanically minded you could change the rods and big end bearings yourself to save on some coin spent on someone else doing the work for you...

Cheers

Bennie

drof351 · Post by **drof351** » Sat Mar 12, 2011 8:38 pm

Thanks for the replies guys. So do they actually stretch? I thought it had spun a bearing. Dont they use factory rods on class n? rally cars? Havent heard of them stretching rods.

littlewhiteute · Post by **littlewhiteute** » Sat Mar 12, 2011 9:18 pm

Conrods don't stretch.

If you do have a piston striking the head, the engine was rebuilt with below minimum spec deck height AND you have a bigend bearing issue.

drof351 · Post by **drof351** » Sat Mar 12, 2011 9:24 pm

thanks little white ute, its been running for about 6 months without a problem. So dont think its deck hieght.

YouTube · Post by **El_Freddo** » Sat Mar 12, 2011 11:30 pm

littlewhiteute wrote:Conrods don't stretch.

This is true but the bolts on the big end bearings can stretch over time, sorry I think I got the message across the wrong way...

drof351 wrote:It started with a little metallic tick a couple of weeks ago, now its sounds like a solid piston hitting head.

After thinking about it further today at work and re-reading your post have you thought that it might be a hydrolic lash adjuster that's on the way out?

Is this subi built for N spec rallying?

Cheers

Bennie

drof351 · Post by **drof351** » Sun Mar 13, 2011 12:03 am

If you heard this thing you'd know it wasnt a lifter, sounds and feels like a pistons trying to bash the head off. haha Na its not built for that but know someone who builds and races suby's and says the rules in his class only allow them to use factory rods.

steptoe · Post by **steptoe** » Sun Mar 13, 2011 1:06 am

You need someone with a snap on viewer to shove into spark hole to see if any evidence. I have heard of rods stretching being a problem with 302 heads on 351 Clevos - different engine same diagnosis - maybe it can happen

drof351 · Post by **drof351** » Sun Mar 13, 2011 1:16 am

So you've heard that the rods actually stretch? Haven't heard of it happening on ej's?

justin35 · Post by **justin35** » Sun Mar 13, 2011 9:08 am

sounds a bit to me like a gudget pin problem,this part holds your piston onto the conrod and if some damage happens here it will allow your piston to slap a bit which in turn will allow it to hit your head..

Post by **TOONGA** » Sun Mar 13, 2011 9:57 am

I've never heard of an EJ motor stretching rods, bending or breaking yes. normally a "stretched rod" means it has twisted or bent under compression / massive heat, and yes the old V8 motors were susceptible to it. but more often than not it was because of the addition of nitrous oxide to the dangerously high revs, which would turn the conrods into an octopus shape.

I would think it is either a big end bearing (it may not have been changed in the rebuild) or a gudgen pin has dropped a circlip and is doing a cha cha cha in the top end.

TOONGA

drof351 · Post by **drof351** » Sun Mar 13, 2011 12:00 pm

It was meant to (paid for) have race bearings fitted and had brand new je forged piston set, gudgeon, retaining rings etc.

rebuilder · Post by **rebuilder** » Mon Mar 14, 2011 12:10 am

u sure its not just a shit load build up of carbon?
do the upper engine cleaner cans take care of the combustion chamber, or is that stuff just for the plenum and valves?
if so give it a shot.

drof351 · Post by **drof351** » Mon Mar 14, 2011 9:32 pm

Na mate no amount of decarb will fix this...

Post by **TOONGA** » Mon Mar 14, 2011 9:57 pm

do a search for piston slap, big end knock or even tensioner noise

I was amazed at just how many people have posted engine noises on the net

http://www.google.com.au/#q=subaru+pist ... 1d1d4b7531

see which one it sounds like

TOONGA

D3V1L · Post by **D3V1L** » Mon Mar 14, 2011 10:36 pm

my wrx had a stretched rod..

and myself, and 2 engine shops concluded it must have happened when one of the big ends fired

davo

YouTube · Post by **El_Freddo** » Wed Mar 30, 2011 10:24 pm

D3V1L wrote:my wrx had a stretched rod..

and myself, and 2 engine shops concluded it must have happened when one of the big ends fired

That's what I'm getting at. Fried big end will effectively "lengthen" the connecting rod through the stretch provided in the big end bolts that hold the bearing in place...

I dunno how close to the top of the cylinder head the piston gets, but if its a fraction of a mm it wouldn't take much for the piston to kiss the cylinder head and create a nasty noise.

I hope you haven't been driving this until you get it sorted out.

Keep us up dated!

Cheers

Bennie