Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: murdock on May 25, 2021, 08:02:06 PM
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Hello, after 40 days the cruzzing pistons have arrived in Spain, if I had bought them elsewhere I would already be enjoying the motorcycle, just today I started a dispute with PayPal to get the money back and the shipping information was updated. 14 days in Tokyo and 25 days nobody knows where, they are still in customs, but when they arrive I must go to the rectifier (as they are called here) to enlarge the cylinders,
what is the gap I need? I have read that Honda works with very little tolerance, but I do not know what exactly, if someone could help me with this I would appreciate it
I have bought pistons of + 0.50
59 mm.
I don't understand the manual very well
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Not sure if this is what you are looking for murdock - this applies to 400Four and not sure if same for 550
http://www.sohc.co.uk/index.php/topic,24199.msg233777.html#msg233777
'1 thou' equals 0.0254mm
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Pisto to bore clearance is 1 thousandth of an inch or 0.025mm and yes it is that small no matter what the people machining the bores say
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There are 2 errors on that chart which will create some confusion !
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There are 2 errors on that chart which will create some confusion !
Which errors 🤔
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There are 2 errors on that chart which will create some confusion !
Which errors 🤔
Piston diameter of 54.47 to 58.49 with a range of 4.02mm ;D that would let some oil past :o
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There are 2 errors on that chart which will create some confusion !
Which errors 🤔
Piston diameter of 54.47 to 58.49 with a range of 4.02mm ;D that would let some oil past :o
Oh yes, I see now Nigel ☺️☺️☺️
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It makes getting the rings in easy though. ;)
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It makes getting the rings in easy though. ;)
Yep, you could throw them in like quoits from the other side of the workshop. ;D
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The other one is in piston diameter - 58.35 is 2.297, their figure shows a piston bigger than the original.
I find it better to substitute MAXIMUM for their word serviceable, it makes more sense to me that way.
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Obviously the author of the manual was not a sociable person or somebody disturbed, I don't know ..jua jua
but I still do not know what the gap would be that I should request from the machinist between cylinder and piston
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if someone fills this photo correctly it would do humanity good
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if someone fills this photo correctly it would do humanity good
Your picture is incorrect. The piston will be in the centre of the bore and as you are using Cruzinimage pistons you need a piston to bore clearance all round at the piston skirt of 1 thou inch which equates to 0.0254mm
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Ok, perfect, thank you very much
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So to fill the figure in on Murdocks' drawing would be two thou , one each side ?
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So I guess it will be like that, the 0.0254 millimetres is 0.25 millimetres, a quarter of a millimetre, 0.0010 inches.
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I'm sorry, between the language and the units of measurement this is a mess, would it be 0.58 millimeters? a little more than half a millimeter
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The Honda chart shows a piston to bore difference of .oo1", which is .ooo5" per side. (half a thou). That's hell of a tight fit ,but that's what the chart says and I believe people have had that done.
How they don't seize up when the piston heats up I don't know .
Careful running in required !
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The Honda chart shows a piston to bore difference of .oo1", which is .ooo5" per side. (half a thou). That's hell of a tight fit ,but that's what the chart says and I believe people have had that done.
How they don't seize up when the piston heats up I don't know .
Careful running in required !
It's correct, and core to Honda design right from early years. Raised silicone aluminium alloy that gives very low heat expansion rate and matches that of the bores.
We had a good illustrative thread on the subject for a forum member's RS 250 single that the engineer shop insisted boring at larger clearance, producing consistent failure and worthwhile searching for.
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The Honda chart shows a piston to bore difference of .oo1", which is .ooo5" per side. (half a thou). That's hell of a tight fit ,but that's what the chart says and I believe people have had that done.
How they don't seize up when the piston heats up I don't know .
Careful running in required !
1 thou clearance on these Hondas using Cruzinimage pistons is perfectly safe and plenty of clearance given OEM Honda pistons the clearance is . 8 thou inch, or even less.
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So I guess it will be like that, the 0.0254 millimetres is 0.25 millimetres, a quarter of a millimetre, 0.0010 inches.
Correct but your engineer that is doing the rebore should know all this.
Edit, just to clarify, I am responding to your drawing above, where you are showing 0.0254mm piston to bore clearance. But I must reiterate, your engineer should know all these measurements and what they mean.
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Julie is right, they SHOULD know thatthe clearance is 1thou but a lot f old school engineers insist that is too tight and will sieze. If they try and tell you that go elsewhereuntill you find one who will do it right or you will burn oil.
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I doubt that the machinist of the places where I can go are even engineers, so I insist on the measurement in millimeters, since the imperial measurement is not handled in Spain except for plumbing,
If I have that measure, I will insist on that, and if something happens it should be under my responsibility and not that of the machinist
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So I guess it will be like that, the 0.0254 millimetres is 0.25 millimetres, a quarter of a millimetre, 0.0010 inches.
I feel that we are confusing murdock with our imperial measurements - just to clarify murdock that for your country you should concentrate on the 0.0254mm (which is not 0.25mm unless) measurement
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https://www.hondatwins.net/threads/maximum-piston-cylinder-clearance.1976/
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creo que ahora si lo he entendido
If the clearance between the wall and the piston is the total clearance, what clearance should I request from the machinist, considering they are aftermarket pistons, 0.001 or 0.002? sounds like the thickness of a hair to me
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creo que ahora si lo he entendido
If the clearance between the wall and the piston is the total clearance, what clearance should I request from the machinist, considering they are aftermarket pistons, 0.001 or 0.002? sounds like the thickness of a hair to me
You are getting yourself so confused for no reason at all. It is the piston to bore clearance which should be 0.0254mm. It really is as simple as that.
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I think what murdock is confused about is:- is the total bore size 0.0254mm bigger than the piston size (or is that 0.0254mm the clearance at each side of the piston)
(I'm playing the devils advocate for the sake of translation here)
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You need the hole (bore) to be 0.0254mm bigger than the piston NOT 0.0254 per side but total
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Correct, that's what the Honda charts show - piston size and bore size, the mean difference being .025mm (.001"). That's the dimension Murdock asked for with his original drawing. But as has been pointed out, check with Cruzzing, are they happy with that clearance for their particular piston material ?
Hope Murdock has stopped scratching his head now after all this up and down (side to side ?) discussion !
Now, let's start again with ring gaps !!!!
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Correct, that's what the Honda charts show - piston size and bore size, the mean difference being .025mm (.001"). That's the dimension Murdock asked for with his original drawing. But as has been pointed out, check with Cruzzing, are they happy with that clearance for their particular piston material ?
Hope Murdock has stopped scratching his head now after all this up and down (side to side ?) discussion !
Now, let's start again with ring gaps !!!!
Having rebored well over 100 SOHC/4's using Cruzinimage piston / ring kits, (well, not me personally but Graham (Trigger) , I just make the tea ☺️) I can confirm the clearance we are talking about is correct.
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Jua jua ..
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They have arrived!
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Just for couriosity, can you weight them? Interested what are weight diff piston to piston (if you have such scale)
I'm currently working on old Jawa 350 engine (2 stroke, 2 cyl) and had quite big difference between 2 pistons (7 grams on 200g piston)
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Weights are in grams, cruzing pistons are + 0.50
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I have already delivered cylinders and pistons to the machinist who accepted the 0.0254 mm without hesitation, I hope it goes well,
Could someone now give me advice on the first break-in or start-up, I know it as softening the engine, so that everything settles
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Ride it normallyand change the oil and filter before using then at 500 miles then every 1500.
Check tappets at 500 then every 3000
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OK, thank you