Help, new m20 head on, but can't align crankshaft to mark!

[rattyvee]

Hi chaps , after searching forums for a discussion of my problem , I think I need to start a new topic , apologies if topic already covered ( please feel free to direct me if so )

1987 325i M20

ok , I know not to turn the cam sprocket with the belt off , pistons will hit valves right ?

so how do I align the crank and cam sprocket now my new head's on , torqued up , manifolds on etc etc , without hitting pistons on valves ?

Moving the crank very tenderly , it will turn 30 degrees before pistons and valves collide. with the crank midway between those limits I can turn the cam 360 freely.

with the cam at timing mark I can't get the crank damper mark to the timing mark on the belt cover.

Part of me feels that ... if the crank turns twice for every single rotation of the cam there must be a position where ( as I turn the cam sprocket round and around ) the crank and cam must at some point be aligned ?

or not

...... trouble is I've a horrible sinking feeling that that *is* true but I ain't going to get them to that position with the crankshaft where it's trapped now ( about 30 degrees clockwise past the mark ) without taking the head off again and setting the alignments BEFORE mounting the head.

weird thing is though , when I google search or forum search I see nothing about having to do that , nothing in any of my 3 manuals , bentley , dempsey or haynes , indeed Dempsey suggests turning the crank 30 degrees off TDC to be sure pistons and valves can't meet while mounting head .......

nobody anywhere says "be sure to put the crank to TDC and the cam approximately to it's timing mark *before* mounting the head"

if I should have , wouldn't someone somewhere be saying so ????

clutching at straws before taking inlet manifold off, head off, buying new gasket , bolts etc etc etc etc

someone tell me it's not necessary please !!!!

Thanks anyone !

[Andyboy]

That was silly. Any manual that says about turning the crank back 30 degrees is bollocks. They must always be 100% correctly at TDC - if the valves don't touch the pistons at 6000 rpm, they're not going to touch during assembly. You're going to have extreme difficulty without taking the head off.....which is what I would do. You'll not make this mistake again I hope.

At TDC, both No.1 valves are closed but No.2 exhaust valve is open and so is No.3 cylinder inlet. Cylinders 4 and 5 have closed valves, both valves on 6 are 'rocking'.
You might be very, very lucky and juggle the cam and crank around (if the crank is at TDC, it needs to be rotated about 60 degrees anticlock to get the first three pistons down enough) but I've a feeling it's a set of bolts and a head gasket for you.

[rattyvee]

no , that's ok , don't be sorry , I don't mind taking the head off if it's necessary , and thanks for saying that it is necessary. I will learn from this clearly , and only mind taking off the head if afterwards , someone says I didn't need to .....

It's strange that I can't find anywhere , no online articles about head gasket replacement .... nothing in my manuals saying anything about setting crank and cam positions prior to mounting the head , when it's now clear that this is critical !

ah well , off to get on with it

[rattyvee]

ahhhhh curiouser and curiouser ....

with the bolts out , and the weight of the head & inlet manifold taken up by a rope or 2 over the garage beams .....


With the crank at TDC with the cam sprocket at the mark , a piston ( guessing 6 ) is hitting a valve or 2 ( guessing 6 again as valves at 1 both closed , and pistons 1 and 6 are up at TDC n'est pas ?

that's very odd

I'll have to take the head right off

that's really really weird

anyone any clues , cos I haven't ..... not a sausage

thanks to AndyBoy for previous response , I was mid thanks when keyboard packed in

[geoffrey]

Have you got the plugs in? If so take them out. It could just be compression fooling you as valves hitting pistons. There is no way valve to piston contact is possible if both pulleys are on tdc marks.

You sure you're using the right marks on the pulleys and engine/head? You must be doing something wrong as it physicly cant be wrong when alligned correctly. Just take your time and dont get fustrated.

[rattyvee]

hey , thanks for helping geoffrey , this really is the weirdest thing

you're right about not getting frustrated ,

completely bamboozled is more like it !

I've taken the head off again , and checked the right valves open at the sprocket mark.

I've got inlet and exhausts on 6 , backed right off by slackening the rocker adjuster cams , and something's still pushing up the head at crank TDC ! has to be piston 6.

plugs are already out, no problem there , but thanks for suggestion.

double checked crank damper is on right , yes

could my pistons be riding up too far ?

have I got the wrong head ? it sure looks like the one I took off ... ( was cracked right along the cam housing )

just keep looking and looking at this head and valvegear - valves open at mark - 2 exhaust , 3 inlet , both at 6 backed off by me - sure looks like the old head's postions .....

derren brown would be foxed by this one !

photos anyone ??

[rattyvee]

I'll tell you what else I find interesting , that piston 1 isn't hitting anything , only piston 6 ( the valves are closed , not partially open like they normally would be , just to sure )

I've got the head unbolted sitting on the block on its gasket

and at TDC the head is nudged up at the back at TDC and back down again beyond TDC


If I've been sold the wrong head , wouldn't it foul at piston 1 too ?

maybe I need to be checking the piston top heights , 1 compared to 6 ?

could my big end have suffered when the old head cracked ?

I didn't hear anything like a bigend problem , was running fine , just suddenly hot.

come on you bmw gurus , your amateur have-a-go mechanic on the front line needs you ....

it's overconfident knownothings like me made this country what it is

[old_skool]

Were all the register marks still visible on the underside of the replacement head? I assume you or the supplier have skimmed it and tested it? You say you backed the rockers off too? You could try plasticine here and there to try and eliminate areas of fouling, or blutack.

I wouldn't have thought that a cracked/overheated head could cause a bottom end issue. You would have problems rotating the crank by hand if there was something that far adrift.

[rattyvee]

oo good point , no , bottom end turns freely and sweetly

that's good

maybe I've bought a head that said it was for an e30 325i , but it's the wrong year or something , certainly looks a lot like the old one

there are marks on the head , it doesn't look skimmed , seller said it had done 6000 miles when he scrapped the car it was in , I'll try to get in touch with him and see if he can enlighten me as to exactly what car it was on.

great suggestion about finding exactly what / where piston 6 is fouling , strange piston 1 doesn't

piece of cardboard over the gasket , then look for dents ?

I'll try that tonight

thanks for the ideas , and very reassuring to realise bottom end prolly ok

I was being philosphical before , you know .... "ahh well , what a wonderful learning opportunity ....."

Cheers !

[daimlerman]

If this is a 325 head,it should have '885' casting mark... a 320 will be '731'...although in theory at least they are interchangable,it is the shape of the chamber that is different along with the valve sizes.

[rattyvee]

Thanks , the valves seem the same size at least ,

I'll look it over for markings , I can recall , whilst searching for this replacement head , using 885 as one of my criteria

maybe the chamber size is different on this one ( still can't figure out why piston 1 doesn't foul though ! )

Thanks for the tip , I'll look it over tonight , any other markings been used on 6 cyl castings that you know of ?

[Templ8e30]

You do know that the crank damper should be off when timing up right ?

There's a notch in the cambelt cover that lines up with a score line on the crank (cambelt) pulley.

You haven't rebuilt the bottom end have you ?, number 6 piston installed the wrong way round ?.

Double check that you have the camshaft and pulley dowel pin located properly.

I've found that if you turn the crank 40 degrees past the TDC mark (clockwise) all the pistons are down the bores to some degree and no valve/piston contact will happen as you turn the camshaft.

Cheers,

Iain T

[rattyvee]

no rebuild of bottom end , and I'm happy now that the bottomn end is fine.

you are quite right , at 40 degrees past tdc I can turn the cam shaft freely without anything colliding , what I can't do is take the crank to TDC without piston 6 hitting the valves even though they are backed off right now.

next test will be cardboard sheets between head and block to see if I can see dents exactly where the fouling is happening

still completely mystified , getting second pair of eyes to look at it tomorrow night

thanks for help !

[rattyvee]

Yay !!!!

problem discovered , nothing damaged , nothing misassembled etc etc etc


guess what , we were all wrong ,

it was the head gasket

My car is an October 1987

GSF sold me a 1987 head gasket , but it's clearly a 1mm or two too small around the bores

The piston at 6 hits the metal ring of the gasket , not the valves , piston 1 strangely doesn't push the gasket up nearly so much.

Diagnostic was by coating the piston in grease , mounting the head , coming up to TDC , taking off the head again and seeing ..... nothing ! Then the penny dropped

did they widen the bore and shorten the stroke in mid 1987 or something like that ?

[Templ8e30]

Curious, the 325i has always had an 84mm bore

I bet it's a 320i/323i gasket with a bore of 80mm.

Cheers,

Iain T

[rattyvee]

yep , I'm sure you are right , oddly GSF have confirmed with me last night that the BMW catalogue shows the right stock code for the victor reinz gasket set I was given , and that gaskets by other manufacturers are totally different , so it's looking like a ballsup at the reinz factory

The new set of bolts have come in a box of 16 , the previoius set had only the required 14

should I worry ? says m20 ( but I suppose could be for 320 or 323 ? )

are the bolts the same from 320/323 to 325i ?

any info gratefully received

john

[daimlerman]

Head bolts should be the same for all M20's,are the replacment set the same length/diameter? Well done for sorting the other issue out,it is usualy the blindingly obvious in the end...

[Brianmoooore]

This whole thread seems to me, to be an excellant advert for zimmerbimmer1 and his genuine parts forum!

[Ziggy]

Wish I'd read this earlier - I'd have looked really impressive if I'd suggested the H/G, but that's what popped straight into my head! Probably because GSF gave me the wrong (M30) H/G set too... I can't remember the last time I went there & actually got the bits I needed. If only they weren't 4x the price, I know where I'd have gone...

[rattyvee]

cheers .

you know what , I'm pretty pleased overall , I love puzzles !

so nice to read my original post and see everything that was a mystery totally explained by the diagnosis

ta !

[andyp]

well what a post, ive been reading it thinking, what is wrong, i never even thought about the gasket, so well done

[Andyboy]

Also make sure you aren't trying to fit a 2 litre head (casting number ends in 731) because the engine will never turn over. I don't agree with the main dealer thing. I only use them for bits you cannot buy from GSF or Euro Car Parts (clips, bits of trim and things like the coolant level sensors). If it has Bosch, Ate, Lemforder, Reinz, Bilstein, Boge, Hella etc on the box then it's okay. Main dealers are too expensive too often and are not infallible - I've seen one try to fit a 2 litre M52 short engine to a 528i............that ran for all of 2 seconds.