Straightening vs milling a head gasket surface - '03 NA V70

[jrschwit]

Basic question: how much "straightening" of a slightly warped head occurs when properly torqued down to a straight cyl block?

Situation: I'm beginning repair of an 5244S engine with a leaking head gasket. I bought this knowing the head gasket was an issue and PO was confident it had never been overheated. On first careful inspection of the head, there is about .005" "dish" in the center of the head which is where the gasket failure occurred. When I put the camshafts in place, I find the center journals are high, enabling a slight rocking when I press down on either end. I have yet to place the head on my granite surface plate to accurately measure the head curvature and determine whether the "warpage" of the gasket surface is accurately mirrored at the cam journals.

Assuming my further analysis confirms that the gasket surface and cam journal alignment are consistent in their "curvature", my best approach will be to straighten the head. Whether professionally by a head rebuilder or by means of the clamping force of the head bolts on reassembly. Thus the basic question: will .005" of curvature be safely removed during torqueing and still provide adequate clamping pressure at the piston sealing surface? The top block surface does appear to be very flat.

I know I can flatten the head gasket surface by sanding or milling but then the cam journals would still not be axially aligned. I've read on this site, IIRC, that Volvo's limit on cylinder head flatness is greater than .005", thus my assumption that considerable straightening of a head occurs when bolted down. I'll note that the car in question is in otherwise very good condition and the engine appears to be worth the effort; very good appearance of cylinder bores, piston surfaces, valve seats, guides, etc. And good compression of cylinders before disassembly, except for leaking number 4.
Jim

[dikidera]

If you think the cam journals are not straight, which they should be, send out the head to have it professionally machined. That way you guarantee the desired results..

However, it is something I know from actual shop owners, if the camshaft bed is curved, this may mean the block is too. So you not only have to straighten the head, but the block as well.

While you will not find information about block warpage of the P2 blocks, there is one from the 960 era that may serve as a guideline

http://www.volvotips.com/service-manual ... anual.html

For the 6-cyl engine it was

Code: Select all

CYLINDER BLOCK


Application In. (mm)


Cylinder Bore

Size C ................... 3.2677-3.2681 (83.000-83.010)

Size D ................... 3.2681-3.2685 (83.010-83.020)

Size E ................... 3.2645-3.2688 (83.020-83.030)

Size G ................... 3.2692-3.2696 (83.040-83.050)

Oversize 1 ............... 3.2755-3.2759 (83.200-83.210)

Oversize 2 ............... 3.2834-3.2838 (83.400-83.410)

Maximum Taper ................................. .004 (.10)

Maximum Out-Of-Round .......................... .004 (.10)

Deck Height ................................. 5.20 (132.1)

Maximum Machining ............................. .012 (.30)

Maximum Deck Warpage

Length ...................................... .020 (.50)

Width ....................................... .008 (.20)

[jonesg]

Basic question: how much "straightening" of a slightly warped head occurs when properly torqued down to a straight cyl block?

Situation: I'm beginning repair of an 5244S engine with a leaking head gasket. I bought this knowing the head gasket was an issue and PO was confident it had never been overheated. On first careful inspection of the head, there is about .005" "dish" in the center of the head which is where the gasket failure occurred. When I put the camshafts in place, I find the center journals are high, enabling a slight rocking when I press down on either end. I have yet to place the head on my granite surface plate to accurately measure the head curvature and determine whether the "warpage" of the gasket surface is accurately mirrored at the cam journals.

Assuming my further analysis confirms that the gasket surface and cam journal alignment are consistent in their "curvature", my best approach will be to straighten the head. Whether professionally by a head rebuilder or by means of the clamping force of the head bolts on reassembly. Thus the basic question: will .005" of curvature be safely removed during torqueing and still provide adequate clamping pressure at the piston sealing surface? The top block surface does appear to be very flat.

I know I can flatten the head gasket surface by sanding or milling but then the cam journals would still not be axially aligned. I've read on this site, IIRC, that Volvo's limit on cylinder head flatness is greater than .005", thus my assumption that considerable straightening of a head occurs when bolted down. I'll note that the car in question is in otherwise very good condition and the engine appears to be worth the effort; very good appearance of cylinder bores, piston surfaces, valve seats, guides, etc. And good compression of cylinders before disassembly, except for leaking number 4.
Jim

i saw a youtube video where a guy had a cyl head that was out of range for corrective machining, he baked and torched the alum head and clamped it to bend the head back the other way.

[abscate]

I think 005” is well within spec for a Volvo head.

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

[beewstew]

Here are the factory service manual specifications. I'd measure the dish with a feeler gauge and a good straightedge and compare it it spec.

https://charm.li/Volvo/2003/V70%202.4%2 ... echanical/

[vtl]

Mill/polish only if the head is straight, otherwise you get warped cam journals. If the head is warped within spec, just check there's no damage on the fire rings mating surface. Also check for straightness between cylinder and cooling passages. Depends on where you are with your measurements you may need to straighten the head before milling it.

If the head and block were both warped bad and for long time, you would see significant wear in cam journals. In that case the engine is FUBAR and not worth working with it.

[jrschwit]

Thanks to all for the replies. Beewstew, I greatly appreciate the specifications link.

Today I cleaned the top and bottom surfaces well enough to confirm the head curvature with a machinists straightedge. Both are curved alike with .005" low in the center longitudinally and less than ,001" transverse. So well within the factory limits. The cam journals are unblemished. The cams rock end-to-end consistent with the curvature. The block has less than .001" deviation longitudinally and no measurable deviation transverse.

I will next bolt the head to the block and check the flatness of the top and see if the cam journals return to acceptable alignment.