Author Topic: Likely to need to hone or bore? Educated opinion sought (Read 7872 times)

Shanedalion · « **on:** March 24, 2012, 01:59:22 PM »

My cb750 motor had one cylinder with rust in it. The piston want badly stuck. The motor had less than 10,000 miles. Should I likely be looking for someone to bore my cylinders and get pistons and rings, or hone my cylinders measure and get rings? I know you can't know for sure, but I know someone has a better idea than I do, and it will decide where I take them for the work. Thanks in advance

tomkimberly · « **Reply #1 on:** March 24, 2012, 02:01:44 PM »

My crystal ball says: Nothing to see, nothing to provide opinon on.

MCRider · « **Reply #2 on:** March 24, 2012, 02:17:28 PM »

Quote from: tomkimberly on March 24, 2012, 02:01:44 PM

My crystal ball says: Nothing to see, nothing to provide opinon on.

Yeah pics always nice.

Its going to depend on how deep the rust pits are and what kind of motor do you want in the end.

If you're looking for a dependable quick back together ride, you can probably hone it ring it and go. Might smoke a little, might not.

If you want an absolutley pristine starting point you'll need to bore it.

Shanedalion · « **Reply #3 on:** March 24, 2012, 02:22:07 PM »

Yep I want it done right. Ill get it bored. Thank you

ffemt2466 · « **Reply #4 on:** March 24, 2012, 03:15:37 PM »

I am at the same point and I'm gonna try to price the difference, trying to keep bike at a budget but also want to do it right. Here is a pic of my cylinder that was stuck.

Shanedalion · « **Reply #5 on:** March 24, 2012, 03:15:57 PM »

Pic. You can see it more than feel it.

KC3 · « **Reply #6 on:** March 24, 2012, 03:24:03 PM »

Bore that out. (You'll be happy you did it right later). I reluctantly honed one about 10 years ago that looked about the same and long story short it ended up two cylinders down after a 2000 mile ride. Hole burnt thru piston #4 and "missing" chunk took out #3 later on...

Shanedalion · « **Reply #7 on:** March 24, 2012, 03:39:18 PM »

I can have it bored and just get different rings, correct? Or I need new pistons too?

KC3 · « **Reply #8 on:** March 24, 2012, 03:42:26 PM »

Why not just do it big and get some oversized pistons while you're getting it bored? Might as well!

Shanedalion · « **Reply #9 on:** March 24, 2012, 03:50:38 PM »

The problem with "might as well" is where do you draw the line? And what else does going oversize involve?

MCRider · « **Reply #10 on:** March 24, 2012, 04:00:07 PM »

Quote from: Shanedalion on March 24, 2012, 03:50:38 PM

The problem with "might as well" is where do you draw the line? And what else does going oversize involve?

Pistons and rings at least. Only the pistons actually add to the cost, since you're getting rings anyway. Boring is probably $90 a hole said and done, with honing, tax and tags.

What happens is often a big bore kit may be cheaper than OS OEMs. The lure ... There are these 836cc kits out there for $110, piston rings and a gasket (I think). But that might push the boring up.

Honing by itself is maybe $20 hole. Some machinists may not want to hone your rust though. But you could hone it yourelf., hmmm...

How appealing is a rat motor to you anyway...

Some of them run pretty good.

KC3 · « **Reply #11 on:** March 24, 2012, 04:00:34 PM »

Well it seems natural to me (being the Tim Allen style horsepower fanatic that I am) to bore those cylinders as large as I can while I'm boring them anyways! You can buy a kit of everything needed somewhere on this site..I believe it's an 836 kit?? (I am a cb550 guy, so I know nothing about such things) Anyone else know what these kits run? I think ebay might even have some!

Cheers-
KC

MCRider · « **Reply #12 on:** March 24, 2012, 04:02:22 PM »

KC3: that's the kit I'm referring to. A few people here have bot them and put a few miles on them. No high mileage tests that I've read yet, but seem fine to me.

Shanedalion · « **Reply #13 on:** March 24, 2012, 04:05:18 PM »

Thank you all. I just wasnt sure if going over size required more than just pistons and rings.
If you hone it you stay with standard size rings correct? Even one size over requires boring correct? Thanks again

MCRider · « **Reply #14 on:** March 24, 2012, 04:08:18 PM »

Quote from: Shanedalion on March 24, 2012, 04:05:18 PM

Thank you all. I just wasnt sure if going over size required more than just pistons and rings.
If you hone it you stay with standard size rings correct? Even one size over requires boring correct? Thanks again

Right honing will retain the stock pistons. New rings should still be a snug enough fit. Even 1 size over(.25mm) requires boring and new pistones.

Shanedalion · « **Reply #15 on:** March 24, 2012, 04:23:02 PM »

Okay, ill hone, measure and proceed from there. Thanks again

tomkimberly · « **Reply #16 on:** March 24, 2012, 04:38:29 PM »

I'd bore and never look back knowing it was done right.

The only additional cost over a hone is the new pistons and if you look around, they are not that hard to find at a good price.

Tom

Grey · « **Reply #17 on:** March 24, 2012, 05:29:21 PM »

Just honing does not guarantee you can use stock rings! You have to measure your cylinder with a bore gauge in several locations to see what the cylinder really is. You can hone .001" or .010". So honing alone is not the answer your looking for. If your using a dingle ball hone, it is not really honing. More of a glaze breaker or cylinder screwer upper. It needs to be machine honed to do it properly.

If it has got like a flash rusting on it. Then honing should take care of it. BUT again if you don't measure first to find out the exact size of the cylinder you won't know if your going to over hone it or not. A good machinist will be able to tell you. You can NOT bore it then just put new rings on the old pistons. It won't work.

You have to measure your pistons first, then your cylinders. Subtract piston size from cylinder size and you have your current clearance. You may be over at that point or may be just under then you can hone, may be. I haven't look up specs for piston to wall clearance on this motor. I'll guess though the p-w clearance is like .0015-.002" +- .0005. The rings need X amont of tension on them to work right and if your P-W clearance is to big it will also have piston slap. Sounds like a diesel with the shirts hitting the cyl wall. If you have to much clearance then you have to over bore, get new pistons and rings.

You only have a couple of thousands to work with in order to do it properly. Find a good machinist with good measuring tools and make him your friend.

Shanedalion · « **Reply #18 on:** March 24, 2012, 05:33:55 PM »

Is there a trusted reasonable person on this site I could send them to to have the work done? Let them decide what needs done?

tomkimberly · « **Reply #19 on:** March 24, 2012, 06:25:23 PM »

You would be better off letting us know where you live (gereral area). Someone might live close enough to help you hands on. As you are new to the forum, I doubt anyone here (without a hefty down payment) would agree to fix your problem without your personal involment.

Tom

Shanedalion · « **Reply #20 on:** March 24, 2012, 06:43:17 PM »

Quote from: tomkimberly on March 24, 2012, 06:25:23 PM

You would be better off letting us know where you live (gereral area). Someone might live close enough to help you hands on. As you are new to the forum, I doubt anyone here (without a hefty down payment) would agree to fix your problem without your personal involment.

Tom

Albany, Oregon. Down payment is fine, and I wouldnt expect to get them back until I pay so not sure why that is so strange. Pretty standard business practice.

tomkimberly · « **Reply #21 on:** March 24, 2012, 06:50:12 PM »

Looks like he is in the Salem OR area. I'm in Southern California. I'm sure someone closer to you will step up. Any members from Portland lurking?

Tom

Shanedalion · « **Reply #22 on:** March 24, 2012, 07:05:28 PM »

Portland may as well be in So Cal, with my work schedule and fuel prices I would be shipping them either way, thats why I was hoping for a recommendation of someone I could trust. May just call the local honda shop, not sure if they do machining though, im sure they can at least recommend someone. Thank you

grcamna2 · « **Reply #23 on:** March 24, 2012, 08:24:10 PM »

Shanedalion,
There may be a sohc4 member as close as Salem,OR.,at least it's possible.

trueblue · « **Reply #24 on:** March 25, 2012, 03:48:40 AM »

Quote from: rotortiller on March 24, 2012, 06:31:22 PM

You'd be surprised at the maximum clearance between the piston and cylinder wa11. New minimum is around or just under .002" with limitations of about .012"

2.394" piston minimum dimension.
2.406" cylinder maximum dimension.
cylinder out of round and taper is .002" maximum
ring gap is about .03" maximum

So you know how much it wore in 10,000 miles before clean up so after cleanup you have something to chew on for remaining lifespan.

Are you saying that on a 750 that maximum piston clearance is 12 thou

, all I can say is you might want to check your figures, 12 thou is .3mm which I believe is more than the first oversize of .25mm, to put it plainly if you have 12 thou clearance the piston would be flopping around like a d!ck in a sock and wouldn't work at all.

News:

Author Topic: Likely to need to hone or bore? Educated opinion sought (Read 7872 times)