engine and drivetrain How to deal with a short upper timing chain cover

[run4wrd]

[*You may want to skip to third paragraph to avoid my intro] 

     First off, great forum. You all have been a tremendous resource in helping me "sympathetically restore" my 1972 BMW 2002tii. I bought the car from her first owner, but she came with a few issues. The previous owner accepted the opinion of a mechanic, who looked at the car a few years ago, "the head gasket is leaking".

     The oil and coolant are both clean, but there is definitely an oil leak. The leak, though, is coming from the front. The previous owner and I agreed the upper timing chain cover probably wasn't machined when the engine was rebuilt seven years ago. 

     *Now, I finally found time to take the head off. All looks really good. However, when I checked the height of the head and upper timing chain cover with my caliper, I was shocked to see the cover was shorter than the head - and not the other way around. I cleaned the head and checked for warping - my finest feeler gauge wouldn't slip through my straight edge. Good news.

     So, what should I do? It seems a waste of precious aluminum to machine a straight head to match the cover.

Do I:

1. shell out $200 for a new cover, and then have it machined to match the head?

2. machine my head to match the height of the frigging cover?

3. use the Elring Dirko silicone I have on hand to bridge the gap along the entire base of the cover?

Dirko is good to 2mm. The gap is of course less than that, but Curil T is only good to 0.1mm, and I don't want to make this a repeated exercise.

     There are many discussions on dealing with machining the upper timing chain cover to match the head, but I have never read a discussion of the opposite problem. I greatly value your assistance with this matter. Again, thank you for all of the helpful expertise.

     

[JerryC]

I have to think there are a number of those covers laying around in peoples' parts piles. It's a $10 - $20 part, used. You can submit a "top timing cover wanted" ad in the classified section with your head's current thickness as a minimum height that you need for the replacement cover.

 

[tzei]

4. Get 2nd hand upper cover that matches you head height or is taller than that and have it machined to height required.

 

pos. 2 is not an option!

[Simeon]

Option 3 will work fine. Obviously the best solution is to get a slightly larger cover and get it fly cut down to the correct size (note someone may have helpfully machined the top surface as well so make sure your measurement takes this into account and is not just based on the total height). 

 

With option 3 get a nice even bead in place, wait for it to set up somewhat and install pushing downward noting the 'give' of the silicon. 

[KFunk]

What about making your own gasket from gasket material that is a little thicker?  Or just using 2 gaskets?

 

No need for metal work here, its not that big of a deal.  

 

edit:er wait, stupid, forgot that its the end of the head gasket.  Then yeah, you could cut the end off an old head gasket and use it to double up, or just cut something out of stock that fits.

Edited August 17, 2016 by KFunk

[Son of Marty]

I'm with KFunk at trace the end of the head gasket and cut the appropriate thickness of gasket paper to try and minimize the gap then, go with the sealer  don't forget to fill the two little holes with sealant where the head gasket and two front covers come together 

[run4wrd]

Sincere thanks for the replies.

I am in the process of calling some local parts people. I hope to get a yes/no on stock in the next few hours.

 

I wasn't very serious about option 2 (machining the head to match the cover), but taking more caliper readings this morning definitely cancels that idea; my measurements for the cover show 128.26mm (!), while all of my measurements for the head show 128.80mm. So, I am dealing with a gap of about 0.54mm. No wonder the engine leaked! I imagine the machinist just made a "best-guess" as to the appropriate amount to take off the cover.

 

So, with that size of gap I think doubling the gaskets at the end would create too much pressure on the bolts. If my local part search comes up empty, I will probably post a wanted ad on this site. I am, though, siding towards Simeon (putting some faith in Dirko). 

 

Regardless, I am going to take the head in to a local European specialist to make sure the head deck is perfect (it's off now, and I don't want any regrets).

 

Again, sincere thanks for all of your input.

 

 

 

[TobyB]

You can just seal it up with your Dirko, or any other gap- sealing... substance.

I have used my UltraBlack on it... with some success...  

 

The double gasket is not a bad idea, but I'll bet you're not 1.6mm too short.

As is using standard gasket- making materials as a shim- but then, glue the piss out

of it with your gasket sealer of choice.  One of the few times I recommend it...

 

The problem is that there's no slop built into the 6 bolts that hold the cover to the head, so a short

cover gets held off the head gasket, and there's a lot of oil slinging down onto that joint between the 2 covers

and the head.  Much less oil, at the top, and that's easier to seal, too, but the cover often won't slide down far enough.

 

You also have to do a dance on installation- you really want to tighten the cover into the corner between

the head and lower cover snugly, but you also want the cover to sit DOWN well, and BACK well.

So you end up gently snugging the 6 front bolts, then tightening the 2 'down' bolts, then loosening

the 6 a bit, tightening them, then loosening the 'down' bolts a bit and retightning... a couple of cycles

seems to really make a difference.

 

hth

t

 

[run4wrd]

Hi again.

I managed to find a cover from a '74 that measured 129.00mm ($28.00 CAD after taxes). I promptly took it and my head to a reputable machine shop. They are going to check the head for flatness and match the cover. Fingers crossed.

I will have some answers in a couple of days. 

Perhaps no Dirko will be needed.

Again, thanks. 

[TobyB]

I think you're set.

 

t

 

[run4wrd]

A final post to conclude the story.

 

The machine shop did a nice job of machining the head with the timing cover attached. They took barely any material off the head, but the bottom of the cover is now perfectly matching.

 

Unfortunately, now with everything on the car, I see that the top of the timing cover rises slightly above the top of the head. 

 

I finally finished reassembling the engine, and I fired it up this evening. Everything seems great. I hope to check the timing this weekend, though, as the car is idling fast. If the timing is okay, I will check for vacuum leaks, before carefully adjusting the idle screw on the idle body. 

 

Again, thanks for the help.

[Tommy]

That's because the small bolts of the cover can't pinch the head gasket quite as much as the head bolts. That shouldn't be a problem.

Sounds that you're doing careful job and you're gonna have good times with your tii

[Simeon]

Sometimes people get all of the gasket faces on a head skimmed. Makes for nice sealing purposes. When you are trying to match a timing cover check the relative position, not just the overall height. 

[Harv]

I think the last time I did it I installed the head, then the cover and then torqued down the head and cover also using Toby's technique. 

 

John

Edited September 2, 2016 by Harv

[run4wrd]

The machine shop I went to didn't think they could machine the cover separately from the head (they weren't sure how to clamp the piece given its shape). That's why they machined the head (just slightly) with the cover attached. On the flip-side, with their approach, I would not be able to machine the top of the cover without removal of the rockers, springs, valves, etc.. No thanks.

 

In hindsight, I perhaps should have properly torqued the cover onto the head before starting the head's torquing sequence. I didn't because I was worried about a shearing stress being created on the timing chain cover bolts - which don't require much torque - as the head was pulled down. In truth, I mainly just wanted to get the head torqued while I knew everything down there was perfectly clean. Perhaps this is naivety. I wish the manual detailed this in slightly more detail, but so far so good. If I have to deal with the lower timing chain cover in the future, I will deal with the gap then. 

 

On a separate note, I am sure unhappy with the quality/usability of the torque angle gauge I picked up for final torquing of the head. I wish the head gasket instructions (that came with the set from WallothNesch) simply instructed me to use a torque wrench.