General Motor rebuild help.. mating surface

[blackbird225]

Disclaimer: I am not asking about my 69 911. I have a rare Volvo motor a B20 variant: B30 6 cyl, 3 liter
Anyways, the question is about IRON mating surfaces. I have had my block honed, new mains, rods resized, new rod bearings, new cam, new cam bearings,etc, on and on. My question is about the mating surface. Somewhere, somehow the mating surface was scratched. If this was an alloy block/head mating I would have it milled and go about my business. This is a very hard iron. I think the shop made these scratches, although cannot prove it. This block has the barrels molded into it- so not easy like our P cars.

Would you take the whole, inline 6 block in to have it milled flat as a head would be? or fill this tiny scratch with jb-weld/copper spray? or some other hokey product? Remember that we are talking about scratch from combustion chamber to WATER jacket here. The worst scratches can be barely detected with a finger nail.

Scratches | Flickr - Photo Sharing!
Scratches | Flickr - Photo Sharing!
Scratches | Flickr - Photo Sharing!

the whole block... ready for reassemble or back to a machine shop :|
http://www.flickr.com/photos/7184021@N07/7197011314

I don't know who else to ask. The people here are the best, so I put it out here for any experts who work on other euro cars. Don't flame or trash me I get one free general question.

Michael

[haasad]

I would simply have it skimmed by flycut or face ground, no issues I can see . Obviously you'll need to understand if this affets any clearance issues elsewhere but I'm not familiar with the engine to comment. I've skimmed many cast iron blocks with fine results.

andy

[AlfonsoR]

In my experience with inline 6's in BMWs and Supra's, and from what I can see in the pictures, I would say it's best to have the block milled. Even though it's tough iron, any engine machine shop will be able to do it, the question is will they do it right?

Caveat is the timing an perhaps other critical clearances might change. I am not familiar with these engines, so you really should ask the folks that talk B30 all day long. On BMW's for example, you are limited to removing a few thousandths because timing is not adjustable unless you do a custom engine CPU. There might be similar considerations for the B30 engine when decking the head or block.

Make sure you take your stuff to a good machine shop. You want it done right the first time since you might be very limited to how much you can remove. You want the right surface finish on the head and the block. I once had an aluminum head that the machine shop left too smooth, had a gasket blowout. Which reminds me, I do like using the permatex copper spray on the head gasket. Only spray the gasket, and only just before you stick the head on the block for final assembly.

If you do deck the block and/or the head, you might want to verify the valve to piston clearances.

BTW, nice looking C303. Beats a hummer any day, HA!

[docrodg]

With lots of experience on iron block water-cooled motors I would have it surface ground by the smallest amount. A perfectly smooth finish is not abolutely required, a little roughness helps it "grip" the head gasket, but just a little roughness. Decking the block is common practice, and failure to do it while surfacing the heads is a waste if the deck is not flat. Tell them you want it blueprinted and they will make sure it is square.

Check the deck height when you get it back and if it is a little low you have a few choices:
1. Thicker gasket - common solution and cheap.
2. Have rods reworked to correct height issue.
3. Different pistons cutom made to a new height.

[blackbird225]

I took it in yesterday. I am going to visit them again today. Just drive by and make them connect that block to a face --again. This rebuild was supposed to take a week or two. 2 months later I am still waiting on head and this block has been to 2 shops and in and out of the van too often. Lessons learned? You need a great machine shop. I think in California they are on every corner or at least within driving distance. Here in Orlando, they exist but are ususally blown away when they see anything other than domestic short block something-or-rather. I shipped the head to a Volvo head specialist and he's so underwater with work he needs to hire James Cameron to help come up for air. He wrote me one night at 3am after catching up! Why not just tell a customer: 'you will wait 4 months for a head, take it to another shop...". Instead, he's like, 'we're two weeks out right now'. Those two weeks were in EEAARLY March..

[blackbird225]

Here are the results:

Block milled | Flickr - Photo Sharing!

Took my flywheel in too. $140 for the block and flywheel. Looks good to me.


I'll snap a pic when the motor goes in.