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Changing rocker cover gasket

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Jambers
Posts: 56
Joined: Mon Aug 28, 2017 9:41 pm
Location: East Midlands UK

Changing rocker cover gasket

Post by Jambers » Mon Jul 02, 2018 10:19 pm

Now this might sound like a dumb question, but that is because I have never changed one before, so pls be gentle!

When replacing the Rocker cover gasket/seal, do you have to use any kind of gasket sealant on the M30, or can you just remove the old and replace with a clean new one and tighten up the bolts?

My only childhood memories are of my dad replacing a gasket using "Red Hermitite" on a Pug 404.... :-({|=
1989 635CSi Manual
2007 Z4M Coupe
Based in the U.K. Leicestershire

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Brucey
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Location: Cambridge, UK

Re: Changing rocker cover gasket

Post by Brucey » Mon Jul 02, 2018 11:29 pm

you can just whack a new gasket in without any sealant or anything, but there are few wrinkles

1) the timing cover gaskets. The upper section of the timing cover is separate from the main part of the head and also bolts through the head gasket. There are two short vertical gaskets which commonly leak. If they are leaking now they will only get worse if you do nothing about it, so now is the time to address that.

2) the upper timing cover thickness. This should be skimmed to be the exact same thickness as the cylinder head. If it isn't there will be parts of the rocker cover gasket that will not seal well.

3) studs or bolts. There are variations but the rocker cover is (usually) held on by a load of studs and domed nuts except for the one that is closest to the distributor which is often a bolt for some reason. In any event all the threads should have helicoil inserts in them already and when you screw the studs (or the bolt) in and out of the holes it is possible to disturb the helicoils.

4) Note that the studs are not all the exact same length necessarily; some have brackets that are mounted using the same nuts, and have longer threads on them.

I normally stick the gasket to the rocker cover using blue hylomar, and then smear a little oil over the other mating faces. This allows the gasket to come away with the rocker cover in future. This means that the rocker cover gasket can be re-used several times over. If it remains stuck to the cylinder head, it is easy enough to damage it when the valve clearances are being set.

Whilst you have the rocker cover off there are other maintenance activities that could easily be done

a) check/threadlock/ lockwire the banjo bolts on the oil spraybar
b) reset the valve clearances (easiest/best done using a (different) feeler gauge between the cam base circle and the rocker, rather than the valve stem and the rocker BTW)
c) check the camchain for wear (by examining how much tensioner stroke is remaining, by looking down the camchain tunnel)
d) check the camshaft lobes for wear
e) run the engine briefly (at idle, cold) with the rocker cover off and check for copious oil flow through the oil spraybar and to all the rocker shafts etc
f) check the valve stem tops to make sure that they are not worn excessively concave

hth

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Jambers
Posts: 56
Joined: Mon Aug 28, 2017 9:41 pm
Location: East Midlands UK

Re: Changing rocker cover gasket

Post by Jambers » Thu Jul 05, 2018 8:55 pm

That is awesome Bruce, thank you so much for that really comprehensive checklist - really appreciated!
1989 635CSi Manual
2007 Z4M Coupe
Based in the U.K. Leicestershire

Drew
Posts: 16
Joined: Mon Mar 11, 2013 7:37 am

Re: Changing rocker cover gasket

Post by Drew » Mon Jul 09, 2018 10:00 am

Hi Bruce, a related question, seemed like a good place to ask it...

I had a pretty bad drippy oil leak coming from the upper timing cover area, just above the chain tensioner, a perfectly normal M30 problem!!

So I replaced the two paper gaskets on the upper cover and used hylomar to seal in the corners, where the two new gaskets meet the CH gasket. Bolted it all up, but in doing so I was conscious that I was not able to seal under the CH gasket, where the CH gasket sits on the lower timing cover.

The leak is much much better, but there is still a small drip. I think this can only be coming from underneath the CH gasket, and I was wondering about taking it all apart again, chopping the front of the CH gasket off {!!} to get sealant underneath it and then sealing the front bit of the CH gasket (now chopped off) to the lower cover and sealing the upper cover onto the CH gasket.

seems a bit extreme I know, but what is the experienced view of such a course of action? Drip is annoying for sure, but not annoying enough to take the head off :-)

thanks
Drew

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Brucey
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Re: Changing rocker cover gasket

Post by Brucey » Mon Jul 09, 2018 6:11 pm

there is a little 'trough' that keeps the tensioner damper filled with oil; if the timing cover gasket is bad near that or the tensioner plug isn't sealed then you will get a leak for sure; more annoying than actually harmful though. There needs to be a big leak before there is much leakage when the engine is running; more usually air leaks in to any small gap instead of oil running out, until the engine is switched off.

In addition some of the bolts in the timing cover can leak oil because the drilling breaks through. In the workshop manual there are some bolts that are meant to be fitted with sealant to stop such leaks.

I wouldn't cut the cylinder head gasket; I might ease it off the top of the timing cover and reseal it by poking sealant or blue hylomar in the gap though.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Drew
Posts: 16
Joined: Mon Mar 11, 2013 7:37 am

Re: Changing rocker cover gasket

Post by Drew » Wed Jul 11, 2018 11:34 am

ta Brucey, yes agreed it's more annoying than serious, just a couple of drips TBH. But I am annoyed by it!!

I had not realised any of the bolt holes went through, I'd assumed they were all blind. I recall on the plate on the back of the head there's one bolt with a non-metal washer, as that one bolt hole is not blind. Will check my books, but I could certainly rectify a couple of bolts with sealant or a crush washer

I tried to ease up the CH gasket but it was never going to work as it would not be possible to clean the surfaces, even if was possible to get sealant underneath, without bending the CH gasket so much as to damage it

cheers
Drew

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Brucey
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Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: Changing rocker cover gasket

Post by Brucey » Wed Jul 11, 2018 2:34 pm

Drew wrote:
Wed Jul 11, 2018 11:34 am

...I had not realised any of the bolt holes went through, I'd assumed they were all blind. ...
well I think they are meant to be....

BTW you may be able to release the head gasket from the timing cover by slipping a razor blade underneath it.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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