FredR

John,

What do you call pressure? I call high pressure 1500 psig in an oil refinery hydrocracker unit or well head pressures of 5000 psig on the gas field I used to work with.

If the breather system worked as it should there would be little more than a good fart's worth of pressure in the crankcase [but it doesn't work very well at all - IMHO] and in a perfect world there would be a small partial vacuum which is supposed to happen but seemingly does not. If the crankcase were to generate 1 psig of pressure the force trying to blow the cover off is about 100 lbs. If the bolt that failed has a shank of 4mm diameter, has a design stress of 20,000 psi and there are 12 of them it would take about 500 psi for the bolts to reach the design stress limit and about 800 psig to shear them. So, you can safely conclude that pressure is not an issue. There is a design issue with these engines, and that is windage trying to escape up through the cam chamber drain channels that completely overwhelms the pissy little breather system and in such circumstance could increase the crankcase pressure a little - mechanically speaking it is irrelevant but that is another matter.

Would the loss of one bolt cause the oil to shoot out if the OP blocked off the hole where the bolt head used to be [that was his question] - no it will not. Will it leak- quite possibly but personally I am not dumb enough or desperate enough to want to find out and hopefully the OP will see the light and do the repair properly.

JayPoorJay

Just my to cents - and not that it gets me ANY closer to solving my problem,,, an answer: that many 10mm bolts are used to adequately snug down a long series and multiple gaskets around a very complex shape. Hence, a bunch of light pressure points.

Honestly,,, because of the vac system and the way air is used, air actually pulled out of the cam area for combustion end re- combustion (what leaks out of the valves as an "efficiency and EPA measure) i thought that it was less than a very and more of a negative pressure. But I could be wrong.

I think all are right and I have to figure out how how to get that damn cover off doing as little damage as possible. This really is bad news.

Thanks all.

Does heating the exposed bolt cap help get the first bolt out of the two part set up? Or is it just twist and pray at this point? Freezing? Anything?

soontobered84

LOL. Fred, there is pressure and then there is PRESSURE!!

What I do know is that my cam cover bolt was missing, and I never had a leak with the engine off or at idle. As soon as I would rev the engine, the heads would start to fill with oil until a stream of oil would squirt out the upper hole where the bolt was supposed to be. I'm not well versed in fluid dynamics, but I'm thinking that if the head is allowed to fill with oil and having a general idea of the pressure that a 928 oil pump can generate, that cam cover with a missing bolt in the lower edge will leak.

I think Jay has the right idea to replace that bolt anyway, so hopefully we don't actually find out the outcome of this exercise.

Jay, Good Luck with the cam cover.

FredR

John,

Glad you appreciated the well intended humour!

I doubt your cam chamber was filling with oil - just remember that it is a splash lubrication system and your camshafts make one hell of a tumble dryer to throw oil around. If there was a hole in the cover in direct line of sight of the oil being slung then indeed it would come straight out.

Jay asked an intelligent question regarding the outcome if he could seal the hole by whatever bodged means his grey matter manages to come up with. The reason for the number of bolts is rather simple. If you have had the cover off [as I am sure you have] you will notice how light it is and how many stiffeners there are inside it and thus the numbers of fasteners has little to do with retaining pressure and everything to do with minimising load distribution thus save weight. I dare say they could have designed it to work with one large bolt in the centre with a "manhole cover" to seal the chamber but thankfully they did not- the cover is quite an elaborate design.

Regarding the ability of the engine to breathe correctly there are two stand out moments I came across over the years. One came from Louie when he sent me a video he took of what was going on inside his driver side cam cover when steaming into a high G long sweeping left hand bend at his local track up in Oregon- that thing really did fill up with oil. Similar thing with Doc Brown with one of his builds on a dyno chucking oil out of open vents [?] on the covers at high rpms. These engines really do struggle to breath correctly when worked hard and it is all probably down to the engine being so low slung/compact.

JayPoorJay

So, I was just fiddling and yes, the bolt is hopelessly sheared and will not come out of the hole with the second part of the two part assembly still attached,,, I guess? So ****, I held my breath and turned out the one just over it. It spun out. One section. I pulled it out and took a look (first time ever on a Porsche CC bolt) and no evidence of loc-tite at least that I could see. Not on that one. I went to a second, put a little pressure on it and got scared (and for good reason). I counted my blessings and stopped. Then replaced the one above the sheared and went to continuing putting my fuel injector rings and spacers back on a set of injectors...

I looked at what I could see of the gasket, an 8th or 16th of an inch sticking out of the frame out around the cover. New-ish looking, shiney black. No cracks, dryness or gummy isht... For now, i think i can only take my chances. Replace the hoses and vac lines I'd originally gone in to check and replace (the Porsche 928 being new to me in everyway), reseal the plenum, inject the injectors in the holes, tuck things back in, make the sign of the cross and fire her up WITH that missing bolt hole plugged,,, for now. For now being key. That,,, with a very keen eye on my fragile area.

I will take the covers off completely, soon enough. Been squirreling away my pennies to have them and the intake powedered... Not looking so forward to it after this.

I'm going to go in with a little dremmel and cut the bracing holding the aux air gizmo to the cover for one,,, cuz now it is the source and focus of all my worry, anger and frustration, lolololololol,,, two because it's ugly and, three it still ain't needed. Then, get me some epoxy or JB and seal up that spot.

Fred, thank you for the clear, thoughtful words, concern and pointers. It matters!!! Unless you really really warn me to not,,, I think I'll go ahead, all warnings heeded and heard.

And,,, I'm still open to suggestions about removing bolts,,,, proceeding. All ears... It's just that the proposition of drilling out and re-tapping 6 sheared off bolts in a 928 cylinder head is NOT so appealing a summer project at this moment. Yes, I've read others experiences and even watched a DIY vid,,, X2.

Thanks folks

DeWolf

That's it. Engine is toast. I'll take it for spares

JayPoorJay

I am always interested in people who seem to gain some strange gratification,,, I dare say joy,,, in someone else's pain, difficulties, problems... It's a uniquely cruel and deranged kinda character defect I encounter sometimes in the world...

But still, yes, I will take the warnings (even yours) into account, Wolf... Sorry for your way of showing up in the world. One can always change. I'll pray for ya...

Strosek Ultra

If the cam cover bolts are stuck and will not come out easily you have to give each bolt a wake up blow. Hit the bolt hard with a hammer. You may have to hit it several times before it will come out. If you cannot hit directly with the hammer, use a steel bar in between. I had this problem when I recently removed the cam covers on the blue car. Just a few of the bolts came out without a blow. In order to increase the pressure on the rubber gasket place 1mm thick washers under the bolt head.
http://jenniskens.livedsl.nl/Technic...4/MyTip483.htm
Åke

JayPoorJay

Thank you Stro! I am so afraid at this point of doing anything else with these bolts. 2 things could happen. 1 is that once I replace the top end of the engine, seal that bolt hole, start her up - if I see ANYTHING like a leak or seaping I will stop and go in for removing the bolts and cover. 2, if all goes well, somewhere down line I fully intend on removing the covers and plenum/intake for a powder coating. At that, I will do what I have to do in the process of removing them. I just really hope that the situation where I MUST remove them happens later than a forced, sooner - if you know what I mean...?

What about heat and hammer? Heat will expand the thread in of the male bolt end,,, help that "wakeup" you talked about, then let it cool and HAMMER time? Then try the turning? What say you? Cooling/freezing and then hammer? I could get some dry ice... Lol,,, yeah, I'm desperate

I'm looking for any advise that will increase the likelihood that I can remove as many of these bolts without a shear.

Strosek Ultra

Jay, this is a common problem with steel bolts getting stuck in aluminium. Heating the aluminum will make it expand and the bolt will come out easier but in this case you need to heat the cylinder head which I believe is not possible to do. It is some distance from the bolt head down to the cylinder head. Do try to strike one of the stuck bolts to see if you can get it out. You may hit it hard but not too hard. You will notice a distinct mark on the bolt head from the blow(s). Be sure to have a good Allen key. When I removed the cam covers on the blue car most of the bolts were stuck. I have not cursed so much in years but I managed to get all the bolts out without destroying any of them.
Åke

JayPoorJay

Hmm. Mine are 13mm bolts. I've never seen one, can't confirm this set up on this machine, but I think that I have the type where the bolts are a 2 part, male female set up. Is that the same set up (2 part) whether it's allen or hex?

FredR

Jay,

The cylinder head bolts are 12mm diameter- no idea where you got 13mm for the cover fasteners from!

Not sure what the shank diameter of the cover fasteners is at its narrowest but if my memory serves me well they shoud only be about 4mm or 5mm max surely?

JayPoorJay

Hey Fred... My failing memory,,, late 40's, lol... Still, I'm sure they were 13mm bolts and,,, the one I am wrestling with - that won't come out of the hole - has a full round barrel type shaft just under the bolt head, nearly the full diameter of the bolt head.

Photos will be forthcoming once home at about 7.30pm. The one bolt that I did remove, a center VCover bolt that I was able to turn out (I'd swear 13mm also), one that held the the top of the bracket I as trying to remove I believe is of the normal skinny straight shaft type. Not sure of the diameter, 4 or 5mm.

FredR

Jay,

The fastener is designed to pull down on a rubber grommet to form a seal and maybe where it does is 13mm or whatever but the narrowest part of the fastener is nothing like that and my expectation is that is the part where it fails under shear. You would need something more akin to a scaffolding pole to break a 13mm diameter bolt.

karl ruiter

There is lots on the forum about this issue, so search around. Its so common that at on point someone was talking about making custom replacement parts that would not fail. Not sure if that ever happened, but you could ask Roger, since if they are available, he will have them. Somewhere there is a post from GB describing the best practice for getting these out. He does it all the time, and I think he rarely breaks one. I seem to recall the the key is to put the tool in the head and smack it (axially) with a hammer a few times to free up the threads. This is what I did, and I was able get all mine out.