S4 Head Resurfacing Specs Dimension Double Check
01-11-2016, 12:53 PM
#16
Former Sponsor
No one answered on the other thread, so I'll start a new thread to ask my question.
I had removed the heads, looked at the corrosion and measured the depth of the worst spots at about .060". Then I set them aside and haven't really done anything, assuming they needed to be welded. Well I finally pulled out the WSM and checked the OA thickness of both heads, and then looked at the minimum thickness specs before requiring the thicker 1.4mm head gasket.
Any experts please let me know if I'm looking at this correctly. The "new part" spec is 147 +/- 0.1mm minimum thickness. I measured the LT head at an average of 149.99mm and the RT head at an average of 149.87mm. So, if I'm understanding this correctly, technically I can have 2.99mm taken off the LT head, and 2.87mm off the RT head and still be within the "new part" specs, correct??
If so, I should be able to have most, if not all of the corrosion spots machined off, without even removing the max allowed. I want to take the minimum amount while still leaving an even, mostly corrosion free surface. I'm thinking about 1.78mm would do it. Am I on the right track with these dimensions? TIA.
I had removed the heads, looked at the corrosion and measured the depth of the worst spots at about .060". Then I set them aside and haven't really done anything, assuming they needed to be welded. Well I finally pulled out the WSM and checked the OA thickness of both heads, and then looked at the minimum thickness specs before requiring the thicker 1.4mm head gasket.
Any experts please let me know if I'm looking at this correctly. The "new part" spec is 147 +/- 0.1mm minimum thickness. I measured the LT head at an average of 149.99mm and the RT head at an average of 149.87mm. So, if I'm understanding this correctly, technically I can have 2.99mm taken off the LT head, and 2.87mm off the RT head and still be within the "new part" specs, correct??
If so, I should be able to have most, if not all of the corrosion spots machined off, without even removing the max allowed. I want to take the minimum amount while still leaving an even, mostly corrosion free surface. I'm thinking about 1.78mm would do it. Am I on the right track with these dimensions? TIA.
You're overthinking this.
Weld the pits, surface the heads minimum, and move forward.
A good machine shop won't do this without pressure testing the heads and doing a valve job when they are done. Needing to spend only $1200-$1500 into a set of 25 year old aluminum heads on a fairly exotic engine is a blessing......the Ferrari and Lamborghini guys are green with envy.
Have the shop show you their giant oven where they pre-heat the heads before welding and then put the heads back in, to cool down gradually, after the welding is done. If they have this and use it, there is very little danger of warpage. No oven=Find another shop.
01-11-2016, 05:08 PM
#19
Former Sponsor
01-11-2016, 07:12 PM
#20
Rennlist Member
Chris, I have access to a couple of sets of '89 heads. One has some bent valves, the other set is off a thrust bearing failure engine. I could take a look at them for corrosion - let me know.
01-12-2016, 10:21 AM
#21
Rennlist Member
Thread Starter
Greg, what I "should" have done was to pick up a decent set from 928 Intl during the 50% off sale, but at Christmas time with four granddaughters, discretionary income is/was non-existent.