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Discussion Starter #1
Hi guys,
I have low compression on one side. On inspection I found the following ;

- Bores look good as new with no wear lip at the top
- Pistons are not scored and measure standard size
- Rings on both cylinders are way out of spec
- Valves look good, not burnt out but I suspect they could do with cleaning and lapping in

My question is, would you replace the pistons even though mine look fine and undamaged or would you just replace the piston rings?

Also, would you replace the timing chain (says DID on it?) or would you just fit a new soft link?

I was going to sell the bike as I have a SV650 which I ride regularly but have since decided to rebuild the 500T engine, tidy up some cosmetics and keep it.

Any advice on where to get piston rings from? I have found some aftermarket rings from Japan for £25 on ebay... is it risky?

Many thanks

Dan 57577043_2038653459567247_3392719045068324864_o.jpg
 

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Dan, since 500T pistons are pretty much impossible to find and since yours measure in spec and look good, I'm sure rings would be enough. The superseded part numbers are the same for the later 450 rings so you should be able to find them fairly easily (though cmsnl.com wants 76 euros per piston). As for the cam chain, if the miles on the bike are reasonable and you're not planning to ride it excessively hard all the time, I'd be surprised if the cam chain needs to be replaced. Obviously since you're already there, it would be wise to pull the valves to inspect and lap them in, but they should be leak-tested at the very least
 

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Discussion Starter #3
Dan, since 500T pistons are pretty much impossible to find and since yours measure in spec and look good, I'm sure rings would be enough. The superseded part numbers are the same for the later 450 rings so you should be able to find them fairly easily (though cmsnl.com wants 76 euros per piston). As for the cam chain, if the miles on the bike are reasonable and you're not planning to ride it excessively hard all the time, I'd be surprised if the cam chain needs to be replaced. Obviously since you're already there, it would be wise to pull the valves to inspect and lap them in, but they should be leak-tested at the very least

Thanks for the reply, you have confirmed my own thoughts to which is good.
Do these look reasonable to you? https://www.ebay.co.uk/itm/75-76-HO...332824?hash=item3d6a7932d8:g:LVoAAOSwq7JT0r0d
 

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Discussion Starter #5
Am I right in thinking CB450 pistons fit from year 67-74 ? The same seller has a pair of these pistons and rings for sale at £65!
 

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I believe the height from wristpin to the top of the piston at cylinder edge is different because of the stroke on the 500T being longer (same bore size) and the skirts of the pistons would have to be shortened to clear the crankshaft as well, due to the longer stroke - which apparently is why 500T pistons are so hard to find
 

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Discussion Starter #7
I believe the height from wristpin to the top of the piston at cylinder edge is different because of the stroke on the 500T being longer (same bore size) and the skirts of the pistons would have to be shortened to clear the crankshaft as well, due to the longer stroke - which apparently is why 500T pistons are so hard to find
Ah yes you're right. The 500T pistons seem impossible to find!

I think I will reuse the original pistons with new piston rings unless David Silver can sort something out for a reasonable price.
 

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Dan, I was in exactly the same situation as you with my 450K5. I found that it was cheaper to buy aftermarket +.25mm piston sets from David Silver rather than buying original NOS standard rings. I had the cylinders re bored, the valves and tips reground and the seats re cut at South Wales Pistons I also replaced the cam chain and all seals in the head.
 

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Dan, I was in exactly the same situation as you with my 450K5. I found that it was cheaper to buy aftermarket +.25mm piston sets from David Silver rather than buying original NOS standard rings. I had the cylinders re bored, the valves and tips reground and the seats re cut at South Wales Pistons I also replaced the cam chain and all seals in the head.
Honda valves are stellite coated. Not to be ground.

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