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Discussion Starter #1 (Edited)
I'm sure most 450 owners are aware that there are no oversize pistons available anymore. I've checked DSS/CMSNL The US dealer network and some less reputable sellers. Two places from the former Soviet Bloc had them listed but when I contacted them they could not locate them. This is quite a dilemma as these bikes keep getting older. I noticed on eBay that cruzinimage_co was selling Non-OEM standard size pistons and rings. After a close look I found that he had oversize pistons and rings listed on his website but that they were also out of stock. After this I contacted him to find out if he had intentions of getting more. There was a communication error as I had to use an existing eBay listing (CB450SC STD rings) to be able to message him. I wanted to know about both pistons and rings but he only responded about rings. As far as oversize rings he would need to make a 500 set (1,000 of each ring) order for his supplier to bother. I couldn't get a clear response about pistons but I would imagine it is a similar situation.

So that pretty much became a dead end. While fumbling around the rabbit hole I did find this crazy German guy who pressed out the sleeves on a CMX450, bored the cylinder and re-sleeved it to fit a pair of Hayabusa pistons. Not sure of their diameter but he says it'll be a 531 or something when he is done (he started over three years ago). Now that is just way too much work IMO. I respect his talent and think it's a cool project but it still stands to be seen if it even works, not to mention the thousands he must have already spent.

So that also became a dead end. However it did get me thinking about pistons from other bikes. Thankfully I found This Honda Piston Size List. Unfortunately it doesn't seem to be complete and only covers Honda. I've been unable to find any sort of list for piston specs (diameter, pin ID, height, and compression height) so it's very difficult to know what might be in the same ballpark. If I had access to a listing like that Honda list I linked I might be able to make some more progress.

I'm hoping you guys will have some insight here. I know Weisco and a handful of others will custom make pistons to your spec but I think that's a little out of reach of the every-man.

Does anyone know the thickness of the sleeve in the 450's? 5th oversize is 76MM, would it be safe to go beyond that? I'm not on a mission for more power here. I just hope to find a viable option for when things get out of spec.


Edit: Grammatical error.
 
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Have you tried the TRW site?
 

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I am very curious about the Pistons as well! I am looking into a Frankenstein motor project for a flat track style bike.


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Discussion Starter #4
Have you tried the TRW site?
Hadn't heard of them until now, but they don't appear to sell engine parts from my limited look around their site.
 

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Venolia will make custom pistons as well, I've had a 74mm set made by them before, long ago, for my 450 drag bike (but never got to use them). You just need to provide them with the specs
 

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The CMX450 uses the same pistons as your's so there's no pistons for those models either. That spec list is wrong on the pin diameter, it's 18mm not 20mm.
I don't know about the sleeves but stock would probably be ok out to 2mm, operative word is probably.
 

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I have been searching the past couple days for some more dimensional information on pistons. It seems the manufactures like to keep that information secret. I came across the following dimensional information but it appears to be only for car pistons but it is a boatload of different makes, all broke up by the piston dimensions. It also lists the OEM item # so you can price them quick and easy. Take a peek.

DAH LIN JIN CO., LTD.--Product Line

Could you run car pistons in a motorcycle engine? Theoretically....?
 

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Yes, car pistons can be used in motorcycles, pretty much they're all the same. There'll be structural differences between the 2 since one is designed for much higher revolutions. Once you've found the right diameter and pin size the next big thing is the crown(top) where the piston to head and piston to valve clearance becomes critical.
 

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The COMP spec is the pin center to top of the piston, sometimes referred to a piston deck. The lower minus numbers could be the valve reliefs or the dish on the piston. Not many, if any, manufacturers are using flat top pistons anymore.
Note that the piston pin diameter is listed as 22mm and the 450's are 18mm. There's no room to bore the rod end out to 22.
 

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Discussion Starter #11
Couldn't a bushing be machined to fit the smaller pin to the larger pin bore on the piston?
 
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That was just for reference. I am still narrowing down a piston.

How much should I worry about the distance between the piston rod end and the recess in the piston?


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If you're referring to the area above the rod to the bottom of the piston deck that's not of much concern. That area is more determined by the thickness of the top. The skirts of the piston to rod is important, that can be easily machined away though.
HamHock, a bushing would be the only practical solution I can think of but what would retain it in place? A hot/cold press fit might work or cause stress on the piston in the area or even come loose under hot running conditions.
 

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Just got the 450 jugs in. Looks like I picked a winner on eBay.

Liner ID: 74.79

Liner OD: 82.3

So there is some meat to it. How thin do you think the walls can go. I read somewhere about 4mm. With a 77mm piston that would give you 5mm and a 530cc.







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If you're referring to the area above the rod to the bottom of the piston deck that's not of much concern. That area is more determined by the thickness of the top. The skirts of the piston to rod is important, that can be easily machined away though.
HamHock, a bushing would be the only practical solution I can think of but what would retain it in place? A hot/cold press fit might work or cause stress on the piston in the area or even come loose under hot running conditions.
The stock "C" clip in the piston would hold the bushing in, and then you could use a Teflon button to hold the wrist pin it.
TOOLS
 

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Discussion Starter #17
Damnit Tools, we're all working in metric and here you come with the imperial system.:rolleyes: So 3.173MM for anyone keeping up. colvinry's measurements show a sleeve thickness of 3.79MM +/- .1MM (I don't trust a slide caliper here). Honda's largest oversize is +1MM which is pretty much in line with what you have said for minimal sleeve thickness, Tools. More or less, maximum bore, without re-sleeving, is 76MM. This is good news! It means we have established one parameter for the piston we need.

Maximum bore: 76MM
 

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These are the closest pistons I have found yet. Still looking for a dome top option. These are cast pistons, flat tops at 77mm. The are out of a 1980 Honda Civic 1.8L EP motor.

They are 7 bucks. LOL!!!!

Can someone with a 450 piston around measure the top to the center of the wrist pin??

Might be able to cut a dome on the lathe and mill the head to up the compression. Then there is the overall length which might be an issue and the valve clearance. Which i am open to making some space with a dremel and some plastigauge. Then there is the matter of the cam chain......dun, dun, dun. Not sure where to even start with that issue.


EP_81Accord Piston.jpg
 

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Discussion Starter #19
If you mill the head you will mess up cam timing as you pointed out. The solution to that is to have the cam sprocket slotted and use a TDC stop with a cam degree wheel to time the cam properly.

I have a loose piston somewhere but I think my calipers are at a friends. I might be able to get some measurements saturday.
 
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