Will honing get rid of this?
- Thread starter Teddy21502
- Start date
AlphaDogChoppers
Science is true whether you believe in it or not.
My gut tells me that's a rebore job. If you hone it a bit, it will be easier to see how bad the damage is. An engine will run pretty well with a surprising about of cylinder damage, but I think you should probably go first oversize on that.
Teddy21502
Active Member
Thanks for all the info guys. The pistons I'm gong to replace, I had to bang on the pretty good to get this bitch un-seized. So overbore it once and get new pistons? Will that mean I need to update my carbs?
Teddy21502
Active Member
AlphaDogChoppers
Science is true whether you believe in it or not.
Tim makes an excellent point. If you have to buy new pistons anyway, get first oversize.
Don't confuse boring oversize with doing an "overbore" job. The change in engine displacement is less than trivial. First oversize is only half a millimeter, or about 20 thousands. It's not to increase displacement, it's just to resurface the cylinder walls.
Don't confuse boring oversize with doing an "overbore" job. The change in engine displacement is less than trivial. First oversize is only half a millimeter, or about 20 thousands. It's not to increase displacement, it's just to resurface the cylinder walls.
HerrDeacon
Over 1,000 Posts
Also, be sure to bore and measure it before getting pistons.
AlphaDogChoppers
Science is true whether you believe in it or not.
HerrDeacon said:
What?!
Who told you that? Cylinders are bored to fit the pistons. Not some theoretical size, but actual measurement of the pistons, and each piston is individually fitted to each cylinder on multicylinder machines.
HerrDeacon
Over 1,000 Posts
Yes, but how do you know what size pistons to buy if you don't know the size of the cylinders. This is an old bike and there is no way of knowing if these have been overbored already, only a measurement will tell you that. You just can't blindly go and order a +1 set if you don't know what state the cylinders are in. You can measure the pistons, but this doesn't tell you anything about the size of the cylinders, they are a matched set. Plus, you cannot know at this point how much it will need to be bored, could be one over, two over, we just don't know. It has to be bored enough to remove the damage, a machinist will be able to determine this for you, and then at this point you get the pistons to match the overbore.
Feel free to buy the pistons first if you like to gamble.
Feel free to buy the pistons first if you like to gamble.
AlphaDogChoppers
Science is true whether you believe in it or not.
A quick honing is all it takes to clean it up enough to measure.
Oversize pistons are labeled. You can usually clean off the crown of the piston and see if it is marked with a 0.5 or 1.0.
I can tell just by looking at it that you don't need to go to second oversize to clean it up.
Oversize pistons are labeled. You can usually clean off the crown of the piston and see if it is marked with a 0.5 or 1.0.
I can tell just by looking at it that you don't need to go to second oversize to clean it up.
So, to summarize
Find a friendly machine shop to measure your cylinders properly. With the promise of boring 2 holes, they should measure them for you for free, to tell you how much bigger you should go to get into a fresh clean hole. You should be paying about $50 per hole for a fresh bore/hone job in the 0.5-1.0mm range.
Once you know how much bigger you need to go in those 0.5mm increments, you can then source pistons. What bike is this?
Order your pistons, rings, some fresh gaskets.
Take the pistons and cylinders back to the machine shop and they should measure the pistons, and bore each cylinder to match a specific piston which they will then mark. Typically they'll mark them on the tops with a marker, with a series of dots denoting the number of the cylinder. This prevents mistakes from bad hand writing or a 2 looking like a 5 upside down. More important when you're working on an 8 cylinder engine I suppose.
Pistons will vary a tiny bit from one to the other, so its important to match the hole to the cylinder. Also do your own research on the clearance you want between the piston and cylinder. The machine shop should be asking you if you're racing your bike or if its just street use etc. as the clearances are different based on application (things change when you're running the bike at redline when racing vs. loping around town at 3000 rpm).
Most important is find a machine shop that works on motorcycles. Car shops will not be able to bore your small cylinders, and if they do, they will be doing it rarely and not have the best tools for the job. Find some local vintage racers and discover the shop they all use. I've used 2-3 shops here in Toronto and now only use Gord Bush Engineering who does a huge number of vintage / race / restoration jobs on motorcycles.
Find a friendly machine shop to measure your cylinders properly. With the promise of boring 2 holes, they should measure them for you for free, to tell you how much bigger you should go to get into a fresh clean hole. You should be paying about $50 per hole for a fresh bore/hone job in the 0.5-1.0mm range.
Once you know how much bigger you need to go in those 0.5mm increments, you can then source pistons. What bike is this?
Order your pistons, rings, some fresh gaskets.
Take the pistons and cylinders back to the machine shop and they should measure the pistons, and bore each cylinder to match a specific piston which they will then mark. Typically they'll mark them on the tops with a marker, with a series of dots denoting the number of the cylinder. This prevents mistakes from bad hand writing or a 2 looking like a 5 upside down. More important when you're working on an 8 cylinder engine I suppose.
Pistons will vary a tiny bit from one to the other, so its important to match the hole to the cylinder. Also do your own research on the clearance you want between the piston and cylinder. The machine shop should be asking you if you're racing your bike or if its just street use etc. as the clearances are different based on application (things change when you're running the bike at redline when racing vs. loping around town at 3000 rpm).
Most important is find a machine shop that works on motorcycles. Car shops will not be able to bore your small cylinders, and if they do, they will be doing it rarely and not have the best tools for the job. Find some local vintage racers and discover the shop they all use. I've used 2-3 shops here in Toronto and now only use Gord Bush Engineering who does a huge number of vintage / race / restoration jobs on motorcycles.
rockcitycafe
I make things.
HerrDeacon said:Yes, but how do you know what size pistons to buy if you don't know the size of the cylinders. This is an old bike and there is no way of knowing if these have been overbored already, only a measurement will tell you that. You just can't blindly go and order a +1 set if you don't know what state the cylinders are in. You can measure the pistons, but this doesn't tell you anything about the size of the cylinders, they are a matched set. Plus, you cannot know at this point how much it will need to be bored, could be one over, two over, we just don't know. It has to be bored enough to remove the damage, a machinist will be able to determine this for you, and then at this point you get the pistons to match the overbore.
Feel free to buy the pistons first if you like to gamble.
I agree and disagree. Yeah, you should have a machinist determine which oversize you need, but no, you don't want to have them bored to a theoretical oversize number before actually having pistons in hand. Why's that you ask? Because I just did a 350 overbore in my shop whose pistons were actually .001" different. I don't even shoot to a "number" at this point, I shoot to the clearance over the piston itself, it's practically a guarantee that you'll fry an engine if you have a machinist bore to a number before getting your pistons in hand, especially with this old stuff where aftermarket is a small business and quality control is somewhat lax
HerrDeacon
Over 1,000 Posts
Yes, well said. The main point I was trying to get at with my post was that you cannot blindly buy a set of pistons without first determining the actual size of the cylinders and the expected measurement after the necessary boring. You cannot determine this from posting a picture on the web, a machinist will need to make this call and will be your guide throughout the process.
Based on the pictures posted, the only advise is to work with your machinist to get it all within spec.
Based on the pictures posted, the only advise is to work with your machinist to get it all within spec.
AlphaDogChoppers
Science is true whether you believe in it or not.
HerrDeacon said:
This is going to sound snarky, but if that is what you were trying to get at, that is what you should have said.
It's actually a very good point.
Teddy21502
Active Member
Wow, All the advice on this forum, I love it. This is for a CB350. OK, so I will hone it first, if that doesn't get rid of the problem areas, I will order .5 over. Only when I have Piston in hand will I take it to a machinist (the only one in my area that will do it is $89 a cylinder which is highway robbery so I'm really hoping a good honing is all it needs).
HerrDeacon
Over 1,000 Posts
AlphaDogChoppers said:
You? Snarky? Never
AlphaDogChoppers
Science is true whether you believe in it or not.
HerrDeacon said:You? Snarky? Never
What?!
