Machine Shop Question

[RustyTank]

Hello again. I'm working on rebuilding the top end of my 1979 GS850.

For those of you with vintage engine rebuild experience, do you always send your head and block to a machine shop be resurfaced, cylinders honed, etc? Is it best practice? I recognize how important it is to make sure the surfaces are flat, and it's an old engine, I've no idea when it was last opened up. Lol, maybe it's a no brainer. Thought I should ask what you guys prefer to do though. I decided to rebuild the top end because it had a chronic oil leak and I thought some some fresh gaskets, piston rings, etc., wouldn't hurt

[zed1015]

No need to skim head or block unless they are warped or have surface damage.
Cylinders only need honing if fitting new rings.
A simple strip and maintenance rebuild of a good engine should only need a good clean up and fresh gaskets ,stem seals etc.

[RustyTank]

No need to skim head or block unless they are warped or have surface damage.
Cylinders only need honing if fitting new rings.
A simple strip and maintenance rebuild of a good engine should only need a good clean up and fresh gaskets ,stem seals etc.

Well, I was planning on installing new piston rings.

[bwringer]

If the bore measures consistently (measuring ring end gap at several points) I use a flex-hone to create a nice crosshatch for seating new piston rings. It sort of looks like a giant bottle brush with abrasive balls on each strand.

One source:
https://goodson.com/collections/flex-hones (the 2-3/4" size should be correct for standard 69mm GS850 bores. I'm about 90% sure that mine is 240 grit).

A few seconds per cylinder using a cordless drill works quite nicely. Keep it moving up and down, use slow speed and lots of motor oil (yep, it's messy as hell) and don't stop or start while in the bore. I support the block with wood over a large pan and do the honing out in a corner of the yard, wearing old pants and boots because oil goes everywhere.

[RustyTank]

tel:2638673[/URL]"]2638673[/URL]]If the bore measures consistently (measuring ring end gap at several points) I use a flex-hone to create a nice crosshatch for seating new piston rings. It sort of looks like a giant bottle brush with abrasive balls on each strand.

One source:
https://goodson.com/collections/flex-hones (the 2-3/4" size should be correct for standard 69mm GS850 bores. I'm about 90% sure that mine is 240 grit).

A few seconds per cylinder using a cordless drill works quite nicely. Keep it moving up and down, use slow speed and lots of motor oil (yep, it's messy as hell) and don't stop or start while in the bore. I support the block with wood over a large pan and do the honing out in a corner of the yard, wearing old pants and boots because oil goes everywhere.

Great info bwringer, thank you. I just watched a vid of a guy doing something similar to hone the barrels of his GS550. Not the exact same tool but similar idea.

[RustyTank]

What do you guys use to make sure the head and block are flat? Just a simple level?

[Nessism]

What do you guys use to make sure the head and block are flat? Just a simple level?

If you open the factory manual for your bike you will find clear instructions on how to check the block and head for flatness. Failing that, you can google "how to check cylinder head for flatness." The procedure in the search is basically same as the FSM procedure.

[zed1015]

What do you guys use to make sure the head and block are flat? Just a simple level?

Use an engineers straight edge or steel rule on its side and try slipping a feeler gauge between it and the clean gasket face in various directions, diagonally etc ( tolerances are in the factory manual ) but chances are the head will be fine.

[RustyTank]

Use an engineers straight edge or steel rule on its side and try slipping a feeler gauge between it and the clean gasket face in various directions, diagonally etc ( tolerances are in the factory manual ) but chances are the head will fine.

Yeah, that's where I was coming from. Wanted to know how to check for gaps, etc. Thanks man. That actually helps a lot.

If you open the factory manual for your bike you will find clear instructions on how to check the block and head for flatness. Failing that, you can google "how to check cylinder head for flatness." The procedure in the search is basically same as the FSM procedure.

Well don't I feel silly. I didn't even think to look in there. Thanks for the heads up Nessism.

[bwringer]

One thing to bear in mind is that this is an air-cooled engine; the head gasket only needs to seal to the block in a ring around each cylinder, the center cam chain tunnel, and at the oil passages at each corner. The head gasket has "fire rings" around each cylinder, and usually a sealing ring around the corner oil passages.

It's common to see "prints" of the old gasket or even corrosion in the "dead" spaces. This is usually pretty harmless and you can create more problems than you solve if you get too obsessive about cleaning up these areas.

Also, depending on which version of the OEM head gasket you end up with (do not even consider aftermarket), you may not need that square o-ring around the center tunnel. Later versions just cover this area with gasket; earlier versions were open here so the o-ring formed the seal.

[Nessism]

Jay from APE has cautioned here before about milling the head to correct flatness issues because that may in part create cam binding issues. The reasoning being that when Suzuki built the head the cam bores were made parallel to the deck surface. If the deck is warped so are the cam bores. Thing is, when tightening the head nuts that flattens the head and straightens it...but not if the head is milled to correct flatness issues. As I recalled he advocated bending the head to straighten it. My memory isn't the best though. Bottom line, I'd be careful about milling the head unless it's just a light clean up cut.

[grcamna2]

Measuring the bores to see whether there is any 'out of roundness'/egg-shaped wear is highly recommended:I don't own an inside micrometer..
I had used a 3-stone spring loaded hone and done a quick glaze-braking in the past on many cylinders and installed new rings.A few of those engines started using oil even with new rings.A bore job is more expensive but if there is elliptical/out-of-round wear in the bores,this will give you back a fully round bore and the rings will break-in nice and you'll have plenty of excellent,consistent compression/ring sealing:the rebuild will last a long time. I would love to have a shop with machinist tools including a precision 4-stone hone such as an expensive Sunnen.. for now I live in a cheap apartment so I bring my parts to a professional machinist and pay the $.

[zuluwiz]

If you are going to a machine shop anyway with your head, try using their surface plate to check flatness. This is a slab of granite ground absolutely flat and is a reference tool for checking flatness. Every machine shop has one.

[RustyTank]

Also, depending on which version of the OEM head gasket you end up with (do not even consider aftermarket), you may not need that square o-ring around the center tunnel. Later versions just cover this area with gasket; earlier versions were open here so the o-ring formed the seal.

Excellent information bwringer. Thanks very much.
Oh, and I have every intention of using OEM gaskets and such

[RustyTank]

Jay from APE has cautioned here before about milling the head to correct flatness issues because that may in part create cam binding issues. The reasoning being that when Suzuki built the head the cam bores were made parallel to the deck surface. If the deck is warped so are the cam bores. Thing is, when tightening the head nuts that flattens the head and straightens it...but not if the head is milled to correct flatness issues. As I recalled he advocated bending the head to straighten it. My memory isn't the best though. Bottom line, I'd be careful about milling the head unless it's just a light clean up cut.

Ok. It sounds like the best thing to do is, once I get the left over gasket gunk off, just check flatness, if it's good, go with it.
Thanks a lot Nessism.

If you are going to a machine shop anyway with your head, try using their surface plate to check flatness. This is a slab of granite ground absolutely flat and is a reference tool for checking flatness. Every machine shop has one.

That's a great idea! Thanks zuluwiz