Signs of a knackerd big end.....

Mon Mar 19, 2007 10:40 pm

What are the signs of a knackerd big end......?

Mon Mar 19, 2007 11:03 pm

If your car has no oil leaks,yet has oil spots all over the back end,start worrying.

Mon Mar 19, 2007 11:06 pm

Jesus325iTouring wrote:If your car has no oil leaks,yet has oil spots all over the back end,start worrying.

Back end of what !! ?

My M20B25 has got a horrible "knock/clatter". it started straight after i changed the head.

Mon Mar 19, 2007 11:09 pm

Sorry,should have said.....

Back end of your car.

Without hearing the engine,i'm no good on advice,hopefully someone will be along soon a bit more clued,the oil thing is the only thing I know for certain!

Mon Mar 19, 2007 11:11 pm

Theres no nasty stuff coming out of the back end.........ooh err.....

I have got a MP3 of the sound......but it sounds like a tractor....

Tue Mar 20, 2007 5:26 am

Does the oil light come on below 1000rpm when at running temp?Just a thought,you say it started after the head was off?Did sir double check the timing marks for the cambelt?....

Tue Mar 20, 2007 7:29 am

just had exactly this.

it will sometimes almost sound as if it is coming from the top end of the engine - SOMETIMES, as the knock can resonate up the cylinder!!

Symptoms are a really loud rhythmic clatter, and as said, you may get the oil light on at tickover, but not always the case.

If you think it may be this, then its easier to do this than whip the head off it, and cheaper too if you do your own spanner work.

Take the viscous off, jack the car up and put it on axle stands. Undo the engine mounts.
Take off as many of the sump bolts as you can but you won't be able to take off the rear ones yet.
Undo the front cover of the gearbox and then jack the box up to raise the engine. Then take the rest of the sump bolts off.
Take the sump away - you may need to jack the box up further for clearance, then undo the big end shell caps using a multipoint socket. Reversal is the bla bla bla. Torque the big end caps to 20 N/m, then thru 70 degrees

Tue Mar 20, 2007 9:00 am

Since this happened right after a head change (immediately after, from the first fire up?), then check the cam belt timing.
IIRC, someone on here recently managed to assemble a 2.5 with a 2.0 head gasket, which caused a loud knocking.

Wed Mar 21, 2007 9:22 pm

Brianmoooore wrote:Since this happened right after a head change (immediately after, from the first fire up?), then check the cam belt timing.
IIRC, someone on here recently managed to assemble a 2.5 with a 2.0 head gasket, which caused a loud knocking.

Yes, the knock/clatter started immediatley from the first fire up of a head change.

Oil supply is good from the spray bar, and the oil light dose not show once the engine has started, either hot or cold, rev'd or not.

What do you mean by "managed to fit a 2.0 to a 2.5" ?

would it be arkward to fit the gasket or head if you was using the wrong gasket ?

Wed Mar 21, 2007 11:39 pm

Bore of a 2 litre is smaller than the 2.5, so a 2.0 head gasket would overhang into the bores and just be hit by the pistons at TDC.
I presume the member who did this was somehow supplied with the wrong gasket and didn't notice as he was putting the head back on.
Have you checked the cam timing yet?

Thu Mar 22, 2007 12:06 am

Sorry to Hijack, my bottom end is knocking, and the oil light comes on at idle after a blast, would I get away with just changing the oil pump and big end and mains? Would I need to worry about the small ends? If they do need sorting, are they bushes or would I need new rods...

Thu Mar 22, 2007 12:09 am

strip and inspect..all parts are available....and top of tec help section is the online etk..for parts illustrations

http://www.realoem.com/bmw/showparts.do ... g=11&fg=20

this link is for m20.

Thu Mar 22, 2007 12:17 am

JonDubber wrote:Sorry to Hijack, my bottom end is knocking, and the oil light comes on at idle after a blast, would I get away with just changing the oil pump and big end and mains? Would I need to worry about the small ends? If they do need sorting, are they bushes or would I need new rods...

Change the short engine!
Because of the common cracking problem of 325 heads, there are a lot more good 325 bottom ends out there than there are heads to go with them, meaning that 325 bottom ends are cheap.

Thu Mar 22, 2007 7:37 pm

Brianmoooore wrote:Bore of a 2 litre is smaller than the 2.5, so a 2.0 head gasket would overhang into the bores and just be hit by the pistons at TDC.
I presume the member who did this was somehow supplied with the wrong gasket and didn't notice as he was putting the head back on.
Have you checked the cam timing yet?

I have not checked the timming yet, i shall do that this weekend. How far out would the timming marks be to cause the knocking ?

I did not notice/cant remmeber seeing the head gasket bores being smaller.

Thu Mar 22, 2007 7:48 pm

if its clatering and showing oil lights

more likely the mains

ends tend to rattle more on the rev down

mains rumble on the way up

be warned if its that noisey
a set of shells wont cure this for long

check the crank lobes are smooth and dullish

if there shiney and have record like grooves/scores
it need a regrind

so best to find another short engine

Thu Mar 22, 2007 9:43 pm

It was I the stupid one who fit the 2.0 headgasket.

It sounded like a tractor but still ran. It was REALLY loud.

Hope you dont have the same problem. If you can, check your part numbers on the receipt for purposes of elimination!

Thu Mar 22, 2007 11:03 pm

adamS wrote:It sounded like a tractor but still ran. It was REALLY loud.

Thats excatly how mine sounds........

The Gasket kit was listed as :

BMW Head set for - 325i 85 on 325e 87-88 525i m20 88 on 525e 87 only

That is the right gasket........isn't it ????

Sat Mar 24, 2007 5:34 pm

Yeah it sounds right! Where did you get the gasket from?

Mine was GSF, both the 2.0 and 2.5 that is!

Sat Mar 31, 2007 10:33 pm

Brianmoooore wrote:Have you checked the cam timing yet?

Now i have !!!!

And it was out..........

When the mark on the Cam sprocket was lined up, the OT mark on the bottom pulley was about 8-10mm (back) away from the timimg mark. The top sprocket was reaching the mark before the bottom mark.
It is quite hard to get the marks to line up exactly.....

It appeared as though there was slack on the "Drive" side (going down) of the belt. I lined up the top mark, slackend the tensioner, locked the top sprocket, moved the bottom pulley forward to line up the OT mark, then re-set the tensioner. but i can not get the marks to line up "Spot on". The knocking/clatter has reduced, it is now just audible above the normal valve tick on tick-over.

Could fitting the wrong belt, ie a 127 tooth belt on a 128 tooth system or vice versa, cause this problem i am having lining the marks up ?

Sun Apr 01, 2007 9:36 am

When I fitted a new belt I set both crank and cam to yhe marks,then found that I had trouble pulling the belt the last half tooth to slot it on to the cam.(as temle30 says I am a big wussie)My solution was to back the cam enough to slide the belt on,then tension the belt and turn the engine over by hand to double check that the marks lined up.I hope that you have not bent any valves by running the engine with the timing so far out.