Lapping (sanding) head down, within spec but still dirty. Keep going?

beewstew · Post by **beewstew** » 06 Oct 2024, 20:32

Working on 2004 xc70 w/ 2.5t engine. Blown head gasket.

Used the Flat Surface+MDF+sand paper+lube method this evening. Lapping went quickly but the paper tore well before the grit was worn off. Went through 6x 80grit, 9x 120 grit because of quickly torn paper. Local big box stores don't have thick glass, so I used a 3/4" 2x4 piece of MDF, clamped to a tablesaw. Per straight-edge it was flat enough

The Haynes manual says the maximum variation in head surface is 0.5mm. Via a straight edge and a feeler gauge I have a small dip in the middle cylinder wall, 0.014 inch on one side 0.010 on the other.

The area around the middle cylinder still has a little bit of baked on carbon/soot.

So, should I keep going w/ 120 or 220 grit paper? I don't want to take too much material off, and the head is now within spec. Why am I nervous? Every youtube video about this method shows the head being lapped down to a completely bright shiny finish, and I'm not there yet.

Exhaust side, 0.014 inch (0.356mm) gap at the 3rd cylinder https://1drv.ms/i/c/7045d4cf7fedc911/ET ... A?e=nmUDca

Intake side, 0.010 inch (0.254mm) gap at the 3rd cylinder https://1drv.ms/i/c/7045d4cf7fedc911/EZ ... g?e=bzfJF4

Haynes Manual says 0.5mm is the maximum variation https://1drv.ms/i/c/7045d4cf7fedc911/ES ... g?e=6Zfw2C

basic setup with purple sandpaper glued to MDF. https://1drv.ms/i/c/7045d4cf7fedc911/EU ... w?e=Rso9fp

Lots of photos: https://photos.app.goo.gl/zQYJ96FpysGtMXwG8

Post by **MoVolvos** » 06 Oct 2024, 20:51

beewstew wrote: ↑06 Oct 2024, 20:32 Working on 2004 xc70 w/ 2.5t engine. Blown head gasket.

Used the Flat Surface+MDF+sand paper+lube method this evening. Lapping went quickly but the paper tore well before the grit was worn off. Went through 6x 80grit, 9x 120 grit because of quickly torn paper. Local big box stores don't have thick glass, so I used a 3/4" 2x4 piece of MDF, clamped to a tablesaw. Per straight-edge it was flat enough

The Haynes manual says the maximum variation in head surface is 0.5mm. Via a straight edge and a feeler gauge I have a small dip in the middle cylinder wall, 0.014 inch on one side 0.010 on the other.

The area around the middle cylinder still has a little bit of baked on carbon/soot.

So, should I keep going w/ 120 or 220 grit paper? I don't want to take too much material off, and the head is now within spec. Why am I nervous? Every youtube video about this method shows the head being lapped down to a completely bright shiny finish, and I'm not there yet.

Exhaust side, 0.014 inch (0.356mm) gap at the 3rd cylinder https://1drv.ms/i/c/7045d4cf7fedc911/ET ... A?e=nmUDca

Intake side, 0.010 inch (0.254mm) gap at the 3rd cylinder https://1drv.ms/i/c/7045d4cf7fedc911/EZ ... g?e=bzfJF4

Haynes Manual says 0.5mm is the maximum variation https://1drv.ms/i/c/7045d4cf7fedc911/ES ... g?e=6Zfw2C

basic setup with purple sandpaper glued to MDF. https://1drv.ms/i/c/7045d4cf7fedc911/EU ... w?e=Rso9fp

Lots of photos: https://photos.app.goo.gl/zQYJ96FpysGtMXwG8

.
See if this helps?
.

.

beewstew · Post by **beewstew** » 06 Oct 2024, 21:52

@MoVolvos yeah, that video is basically what I was doing, but with WD40 on the paper to control the dust. What I don't understand is if sanding down to 0.002 inch (as that guy does) actually makes for a better repair when the spec (per Haynes at least) is variations of "no more than 0.5mm" which is about 0.019 inch.

Post by **matthew1** » 06 Oct 2024, 22:30

That difference is a magnitude

Post by **MoVolvos** » 06 Oct 2024, 23:13

beewstew wrote: ↑06 Oct 2024, 21:52 @MoVolvos yeah, that video is basically what I was doing, but with WD40 on the paper to control the dust. What I don't understand is if sanding down to 0.002 inch (as that guy does) actually makes for a better repair when the spec (per Haynes at least) is variations of "no more than 0.5mm" which is about 0.019 inch.

.
You have two issues. You need to sand down further exactly per the video and once those marks are gone you'll probably solve the second which is being at 0.002 rather than 0.5. He has an update on using WD40 for speed not dust control.
.

.

Post by **vtl** » 07 Oct 2024, 05:37

You are doing it wrong. First off, this is a Swedish car, right? So you MUST use IKEA kitchen table!

Also a polished 3/8" or thicker glass on top of it, and let it sit for a few days to relax and straighten. My setup was under 0.05 mm (0.002") flat in the work area.

: 1.jpg (86.67 KiB) Viewed 375 times

Grit 320 sandpaper. WD-40 is must, IMO.

: 3.jpg (65.32 KiB) Viewed 375 times

: 5.jpg (48.18 KiB) Viewed 375 times

Also Dykem Blue is good to control the results.

: 2.jpg (72.6 KiB) Viewed 375 times

: 4.jpg (90.22 KiB) Viewed 375 times

You want to remove all dark spots (depressions in metal) between fire ring and cooling channels. This is where gaskets fail. Also no dings in fire ring area at all.

: 6.jpg (72.99 KiB) Viewed 375 times

End result.

: 7.jpg (55.34 KiB) Viewed 375 times

You head seems to be warped a lot, or maybe sanding setup is not flat enough.

Post by **MoVolvos** » 07 Oct 2024, 14:48

vtl wrote: ↑07 Oct 2024, 05:37 You are doing it wrong. First off, this is a Swedish car, right? So you MUST use IKEA kitchen table! Also a polished 3/8" or thicker glass on top of it, and let it sit for a few days to relax and straighten. My setup was under 0.05 mm (0.002") flat in the work area.

1.jpg

Grit 320 sandpaper. WD-40 is must, IMO.

3.jpg

5.jpg

Also Dykem Blue is good to control the results.

2.jpg

4.jpg

You want to remove all dark spots (depressions in metal) between fire ring and cooling channels. This is where gaskets fail. Also no dings in fire ring area at all.

6.jpg

End result.

7.jpg

You head seems to be warped a lot, or maybe sanding setup is not flat enough.

.
Superb!
.

beewstew · Post by **beewstew** » 09 Oct 2024, 09:49

@MoVolvos @matthew1 @vtl Here's where I finished. Still one small black spot between the middle cylinder and exhaust sided coolant passage.

https://1drv.ms/i/c/7045d4cf7fedc911/Ee ... Q?e=pjKIhf

I guess I could keep going, but it seems like I'm getting close to taking too much material off the head and the remaining divot is ~ 0.004 inch deep, which seems within acceptable spec per Volvo Manual.

https://1drv.ms/i/c/7045d4cf7fedc911/EY ... g?e=fKp7FJ

Front-rear.0.50 mm
Lateral.0.20 mm
Cylinder head height.129.00± 0.05 mm
Maximum machining.0.30 mm

https://charm.li/Volvo/2004/XC70%20L5-2 ... chanical/

Never got finer that 120grit paper. Procedure was 50-100 slides across three sheets of paper and then a photo to document progress. Lots of pictures here: https://photos.app.goo.gl/zQYJ96FpysGtMXwG8

Post by **vtl** » 09 Oct 2024, 09:53

Yea, keep sanding. You want a flat head between cooling passages and fire ring, or coolant will erode the head/gasket. I see another low area left to the next cylinder.

Post by **volvolugnut** » 09 Oct 2024, 14:38

I have no specific knowledge of head flatness, but it seems to me that the illustrations of flatness deviation is correct. It is OK to have a consistent bend in the head within the spec and the head bolts can pull the head into flatness.
It you have a concentrated, localized 'divot', the head bolts will not be able to pull the head into good contact everywhere and you will have a leak.
If you remove too much thickness from the head, you can increase the compression ratio too much. This can cause ping and the need for higher octane fuel. This used to be a hot rodder trick to increase power.
Also, when you remove material from the head surface, the valves get closer to the pistons. I don't know how close they are in stock condition and how much removal will be a concern. You can do a trial assemble with head gasket torqued (maybe with the old gasket?) and modeling clay on the piston under each valve. Then measure the compressed clay thickness to know the new clearance. The internet and others may know what clearance is too close.
volvolugnut