One Broken Head Stud Rebuild Now?
12-28-2003, 09:59 PM
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One Broken Head Stud Rebuild Now?
Hiya All,
I have owned my first Porsche for 2 months now (its a 1979 911 SC with 106000 miles) and thought I would give it a service, oil, filters and valve adjustment. When I took the rocker covers off to adjust the valves I found one broken head stud (exhaust side). It was missing the nut off the end of it as well which makes me wonder if the P.O. knew about the problem (he didn't mention it of course). I didn't get a PPI but got the car cheaply enough by UK standards and don't feel that I have the right to feel hard done by the P.O. The amount I saved would go a long way towards paying for a rebuild. I have read in various places that you should rebuild immediately and others have written that some engines can run a long time without further problems as long as you check often for any other broken studs as more than 1 broken stud requires immediate attention. Are there any other checks or signs that I should look out for that should be done apart from looking for oil leakage between the head and cylinder? The engine runs great apart from hunting when cold, doesn't burn oil only leaks it and sounds great no abnormal noises at all and has lots of power especially above 4000 rpm. I have always gone easy with it till it warms up fully and am driving it very gently for the past 500 miles or so since I found the broken stud. I should mention that funds are limited and I hadn't expected or planned for the cost of a rebuild so soon. Is it possible to change the studs to the type used on the inlet side only and put everything back as it was or is reconditioning the top end a must do while you are in there? I have bought the Bentley service manual as well as Wayne Dempseys How to Rebuild & Modify 911 Engines and plan (hope to if I can get brave enough) to do the work myself. I have read his comments (Dempsey) of when to rebuild but would appreciate advice from others who have been in this position.
thanks in advance for all who reply
regards
Billski
1979 911 SC
1986 Heritage Softail
1972 MGB Roadster
I have owned my first Porsche for 2 months now (its a 1979 911 SC with 106000 miles) and thought I would give it a service, oil, filters and valve adjustment. When I took the rocker covers off to adjust the valves I found one broken head stud (exhaust side). It was missing the nut off the end of it as well which makes me wonder if the P.O. knew about the problem (he didn't mention it of course). I didn't get a PPI but got the car cheaply enough by UK standards and don't feel that I have the right to feel hard done by the P.O. The amount I saved would go a long way towards paying for a rebuild. I have read in various places that you should rebuild immediately and others have written that some engines can run a long time without further problems as long as you check often for any other broken studs as more than 1 broken stud requires immediate attention. Are there any other checks or signs that I should look out for that should be done apart from looking for oil leakage between the head and cylinder? The engine runs great apart from hunting when cold, doesn't burn oil only leaks it and sounds great no abnormal noises at all and has lots of power especially above 4000 rpm. I have always gone easy with it till it warms up fully and am driving it very gently for the past 500 miles or so since I found the broken stud. I should mention that funds are limited and I hadn't expected or planned for the cost of a rebuild so soon. Is it possible to change the studs to the type used on the inlet side only and put everything back as it was or is reconditioning the top end a must do while you are in there? I have bought the Bentley service manual as well as Wayne Dempseys How to Rebuild & Modify 911 Engines and plan (hope to if I can get brave enough) to do the work myself. I have read his comments (Dempsey) of when to rebuild but would appreciate advice from others who have been in this position.
thanks in advance for all who reply
regards
Billski
1979 911 SC
1986 Heritage Softail
1972 MGB Roadster
12-28-2003, 10:14 PM
#2
RL Technical Advisor
Hi:
If it were me, and if I did not have the budget to perform a full rebuild, I would simply pull the heads and cam towers (as complete assemblies), pull the cylinders and replace all 24 studs with the later, 993 ones.
You'll buy a complete gasket kit, and the studs is all.
If it were me, and if I did not have the budget to perform a full rebuild, I would simply pull the heads and cam towers (as complete assemblies), pull the cylinders and replace all 24 studs with the later, 993 ones.
You'll buy a complete gasket kit, and the studs is all.
12-28-2003, 10:26 PM
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Hi Steve,
Thanks for the quick reply. All the reading I have done so far involves complete rebuilds and hence complete stripdown. I'm not sure what you have to remove in order to take the cam towers off as a complete assembly but I am assuming the cam chain must come off first. What else is involved?
regards
Billski
Thanks for the quick reply. All the reading I have done so far involves complete rebuilds and hence complete stripdown. I'm not sure what you have to remove in order to take the cam towers off as a complete assembly but I am assuming the cam chain must come off first. What else is involved?
regards
Billski
12-28-2003, 10:38 PM
#5
RL Technical Advisor
Billski:
I would not drive the car until its repaired; the loose heads are beating up and down on the cylinder and will damage these sealing surfaces pretty quickly. If you do a valve job, this will not matter much as those parts would be reconditioned.
To get the heads and cam towers off, the chains must be removed of course,....
Get a copy of the Bentley Repair manual for the SC and that will get you through this.
I would not drive the car until its repaired; the loose heads are beating up and down on the cylinder and will damage these sealing surfaces pretty quickly. If you do a valve job, this will not matter much as those parts would be reconditioned.
To get the heads and cam towers off, the chains must be removed of course,....
Get a copy of the Bentley Repair manual for the SC and that will get you through this.
12-29-2003, 02:27 PM
#6
Intermediate
Billski,
I was in the same boat two years ago. I have a 1980 Euro 911SC and it had two broken lower headstuds with 107,000 miles on the engine. I pulled the engine out and tore it down to the case and replaced all 12 lower dilivar head studs with steel ones (same part number as the top 12 row of headstuds) and put it all back together. The headstuds and needed gaskets came to about $300 USD. I have put on 7,000 miles over the last two years and the car runs great. The engine needed to be repaired, not rebuilt. When it needs to be rebuilt, I'll do a complete rebuild.
If you have to pay to have someone do the work for you, expect to pay $2,500-3,000 to do the studs. Because the labor cost is so high, most people end doing a top end rebuild at the same time to avoid having to pay for all that labor again when a top end rebuild is warranted.
I was in the same boat two years ago. I have a 1980 Euro 911SC and it had two broken lower headstuds with 107,000 miles on the engine. I pulled the engine out and tore it down to the case and replaced all 12 lower dilivar head studs with steel ones (same part number as the top 12 row of headstuds) and put it all back together. The headstuds and needed gaskets came to about $300 USD. I have put on 7,000 miles over the last two years and the car runs great. The engine needed to be repaired, not rebuilt. When it needs to be rebuilt, I'll do a complete rebuild.
If you have to pay to have someone do the work for you, expect to pay $2,500-3,000 to do the studs. Because the labor cost is so high, most people end doing a top end rebuild at the same time to avoid having to pay for all that labor again when a top end rebuild is warranted.
12-30-2003, 11:30 AM
#7
Race Car
Agreed, stop any further use of the vehicle until problem is resolved.
While you may be able to get away with just replacing the studs/gaskets now...further down the road you may wind up having to replace that cylinder and head, even possibly have to get work done on the case due to further damage.
I've seen it, it's nasty!
What happens is that the cylinder and head start to move on each other with compression and wear the mating surfaces out, also where the cylinder goes into the case, etc.
One head stud isn't bad, but that usually means there are others to follow as they corrode through.
While you may be able to get away with just replacing the studs/gaskets now...further down the road you may wind up having to replace that cylinder and head, even possibly have to get work done on the case due to further damage.
I've seen it, it's nasty!
What happens is that the cylinder and head start to move on each other with compression and wear the mating surfaces out, also where the cylinder goes into the case, etc.
One head stud isn't bad, but that usually means there are others to follow as they corrode through.
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12-30-2003, 10:10 PM
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Definatly stop driving the car. The wear on the surfaces and potential for more damage is too great. If your budget is really tight, doing just the studs and gaskets is not a bad idea. With help from the board and manuals, you can get through it.
Matt
Matt
12-30-2003, 10:35 PM
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I had more pulled headstuds than I could count when I bought mine (several per cylinder). So I tore it down for a full rebuild. Luckily my machine shop was able to save my heads but I fully expected to buy replacements. Take a look at the pic to see what can happen with pulled or missing headstuds.
12-31-2003, 02:36 PM
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Hi All,
Thanks for all of the replies I have decided that I am not driving this car till I have sorted out the problem. I have been having a good read in the Bentley Service manual as well as Wayne Dempsey's rebuild book and think it I will be able to attempt the rebuild myself. I am looking to buy the tools first thing in the new year and I will let the condition that I find the parts in dictate how much work I need to do.
Is it a good idea to have a compression and leakdown test done before I strip it down to see what condition the bores are in or will looking at them tell me just as much?
many thanks for the good info.
have a Happy New Year
regards
Billski
Thanks for all of the replies I have decided that I am not driving this car till I have sorted out the problem. I have been having a good read in the Bentley Service manual as well as Wayne Dempsey's rebuild book and think it I will be able to attempt the rebuild myself. I am looking to buy the tools first thing in the new year and I will let the condition that I find the parts in dictate how much work I need to do.
Is it a good idea to have a compression and leakdown test done before I strip it down to see what condition the bores are in or will looking at them tell me just as much?
many thanks for the good info.
have a Happy New Year
regards
Billski
01-03-2004, 11:58 AM
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There are some anecdotal stories about people driving cars, thousands of miles with a broken head stud. They don't even know whats going on!
Sometimes you can hear it, and sometimes not.
The machined sealing surface of the head can get damaged. You may not see the damage with the naked eye, but can, with a small magnifying glass.
You may not be exactly sure just how long you have been motoring with the broken stud. Therefore, you should have an experienced Porsche mechanic inspect the heads as above. Typically, the heads will only need a light flycut (0.25mm) to renovate them. Use 0.50mm base gaskets upon reassembly to restore cyl/head dimensional relationships.
Sometimes you can hear it, and sometimes not.
The machined sealing surface of the head can get damaged. You may not see the damage with the naked eye, but can, with a small magnifying glass.
You may not be exactly sure just how long you have been motoring with the broken stud. Therefore, you should have an experienced Porsche mechanic inspect the heads as above. Typically, the heads will only need a light flycut (0.25mm) to renovate them. Use 0.50mm base gaskets upon reassembly to restore cyl/head dimensional relationships.
