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As part of replacing head gaskets I am going to have the heads skimmed. I have them stripped down but wondered if the dowels for the cam bearing caps need to be removed. They seem pretty tight so didn’t want to force the issue without first understanding whether these are normally removed.
Don't remove the dowels for the cam caps. They are not removed even with a "full head job."
EDIT: Do, however, remove the oil check valves. Leave the seats alone unless they are loose.
On that subject, as per 928Myles, examine carefully the head deck surface especially around the fire rings. Look for pitting due to corrosion. If you have pitting within 1-2 mm of the fire rings you should get the pitting fixed (via welding.)
Regardless of pitting, my advice is to find a machine shop with extensive experience in 928/944/924/968 heads and have them do a full head job. Several exhaust valve guides are almost always 'too big' and the original spec is as Doc Brown once told me "So big you can put the valves in sideways."
In my experience you'll also find at least one bent valve.
And you might as well replace valve stem seals while you're there.
An experienced machine shop can do a "full" head job for $1 to $1.5k per head depending upon the amount of welding required. If extensive welding is required the cost per side can go up dramatically. But, there's no way to tell for sure until the deck is soda blasted.
Since your heads are already on the bench... Do it once. Do it all the way.
I use Allied here in Atlanta and the most I've ever paid is $425 per head - that includes complete rebuild and welding.
Sadly, my local guy is retiring but his price to rebuild a pair of heads - I provide the valve stem seals - and he charges $450 to rebuild two heads that do not need welding.
Don't remove the dowels for the cam caps. They are not removed even with a "full head job."
EDIT: Do, however, remove the oil check valves. Leave the seats alone unless they are loose.
On that subject, as per 928Myles, examine carefully the head deck surface especially around the fire rings. Look for pitting due to corrosion. If you have pitting within 1-2 mm of the fire rings you should get the pitting fixed (via welding.)
Regardless of pitting, my advice is to find a machine shop with extensive experience in 928/944/924/968 heads and have them do a full head job. Several exhaust valve guides are almost always 'too big' and the original spec is as Doc Brown once told me "So big you can put the valves in sideways."
In my experience you'll also find at least one bent valve.
And you might as well replace valve stem seals while you're there.
An experienced machine shop can do a "full" head job for $1 to $1.5k per head depending upon the amount of welding required. If extensive welding is required the cost per side can go up dramatically. But, there's no way to tell for sure until the deck is soda blasted.
Since your heads are already on the bench... Do it once. Do it all the way.
Flycutting, resurfacing the heads is not very difficult to do. Do cut both heads equally much. The cam timing will be affected.
Pictures show when I did the head for our old Volvo. I am happy I managed to adjust the machine for a very fine smooth surface.
Åke
Flycutting, resurfacing the heads is not very difficult to do. Do cut both heads equally much. The cam timing will be affected.
Pictures show when I did the head for our old Volvo. I am happy I managed to adjust the machine for a very fine smooth surface.
Åke
I have not checked the WSM but there is probably a machining specification of permissible amount that can be removed. Although the amount is totally limited by the valve seat in any case.
I cant picture any effect this would have on valve timing since the valve timing is adjustable and set while the engine is going back together. Maybe I am missing something
The height of a new cylinder head is 146,9 - 147,1 mm. Normal head gasket thickness 1,1 mm. Permissible height after machining 146,6 - 146,8 mm. Use thicker head gasket 1,4 mm (according to WSM).
This will not alter compression ratio, cam timing nor how the waterbridge will fit to the heads.
If you need to remove more than the above amount (0,3 mm) you will be faced with some problems like the cam
timing will be late (which can be adjusted) and the waterbridge bolt holes may need to be altered. The CR will be increased.
I have checked a cylinder head and you can remove about one mm before you touch the intake valve seat rings.
Picture is showing a ported head with standard size valves.
Åke
07-04-2020, 04:22 PM
Skimming S4 heads advice
