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Doing a top end rebuild on my '73 350G. First-timer getting this deep into the engine, feeling pretty good about it so far but am hitting the point where I need some advice-
To preface my questions, I started this job because the left side was not firing and I came to find that there was bad compression- about 30 if I remember right. Compression on the right side was around 150psi. I added some oil to the left side and tested again and it came up to about 90 psi, so I figured it was rings.
So i've taken it down, and took measurements throughout both cylinders, and found that BOTH of them were out of standard specs, for the most part.
Both sides had a total average measurement of 2.5210" with the largest measurement in a couple places in each cylinder being 2.5217" (keeping in mind that this was my first time using snap gauges and micrometers, so error was likely, however I took over 35 measurements in each cylinder to double check, then averaged measurements in each position)
So, do I need to bore? How much? I've seen that Common Motor has oversized pistons up to 2mm over, but the factory manual says to replace the sleeve if boring over 1 mm is needed.. maybe im misunderstanding the language in the manual? Anyway, any advice is appreciated!
Thanks.
 

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If the FSM says that (and I don't know that for sure) it's just Honda being typically overprotective in the interest of reliability, as always... my 450 (and a previous one as well) is bored 4mm oversize on the stock sleeves and I ride it on the weekends like any other street bike I've owned in 50 years of riding - and it survived the heat of Barber last October as well, riding it around the grounds every day for the entire week (I was there with a vendor so longer than the 3 day weekend the public sees) including all the traffic of Friday through Sunday. Going 1 to 3mm over on stock sleeves is not that big a deal
 

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Honda only offered oversize pistons up to 1.00 mm oversize, for anything bigger than that they expected to sell you a new liner or cylinder. I would only go as big as is necessary to clean up the bore, the more meat you leave in the cylinder the more room for future rebuilds. Parts in the .25 to 1.00 oversize range will likely be easier to find in the future, using genuine Honda parts means quality will be consistent also.
 

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Let your machinist tell you how much you need to bore to clean things up. The cost will depend on how many "passes" he thinks he has to make.
Then order what he says - parts in hand, he'll be able to do a proper job.
 

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It had all been said, and i heard a lil voice in my head that said zip it!!
Thats my story, and i'm sticking to it!

Sent from my SM-N920R4 using Tapatalk
 

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If it is just a road-going bike: Go as large as you need to, not more.

You can go up to 67,5mm, if you want. That will work in the original liners. But you'd have to but aftermarket pistons like from Todd Henning Racing. Honda sells piston up to +1mm in increments of .25mm. If you buy Honda pistons, be sure to get the piston rings that have the three part oil ring.
 

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If you bore fore displacement, that limits your future - if you ever need another bore you're screwed. Largest I ever saw was 12'th over (3mm) - if your 12'th over fails you'll need new sleeves.
Otherwise, just bore enough to clean the cylinders up, leave yourself some headroom in the future.
 

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If you bore fore displacement, that limits your future - if you ever need another bore you're screwed. Largest I ever saw was 12'th over (3mm) - if your 12'th over fails you'll need new sleeves.
Otherwise, just bore enough to clean the cylinders up, leave yourself some headroom in the future.
Bill, you did see my post above, right? I've done S-16 (with high compression) twice with great long-term reliability. Granted, it's at the end and if anything happens you need new sleeves or a good used cylinder, but it's more reliable than people give it credit for as long as you don't do dumb stuff that you shouldn't do anyway, like idling in summer heat for a long time, it's fine for a very long time. It doesn't get much hotter than Barber last October and my bike did just fine running around the grounds all week long, including in the very increased traffic from Friday on when the public came in droves
 

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Bill, you did see my post above, right? I've done S-16 (with high compression) twice with great long-term reliability. Granted, it's at the end and if anything happens you need new sleeves or a good used cylinder, but it's more reliable than people give it credit for as long as you don't do dumb stuff that you shouldn't do anyway, like idling in summer heat for a long time, it's fine for a very long time. It doesn't get much hotter than Barber last October and my bike did just fine running around the grounds all week long, including in the very increased traffic from Friday on when the public came in droves
Like I said above, I've never personally seen anything bigger than 12 - I'm not doubting the existence, just the rarity........
And again, if you blow out those 16's, those sleeves are probably done for.
 

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The best answer to the question in your title is:

ONLY YOUR MACHINIST KNOWS - Unless you own a Bore Gauge and have the skills to read it.

Let them tell you how much has to be removed.

Again like already said - Unless you are going for Max Size... but REALLY... These motors are already pretty much as tricked out for performance as needed for Street purposes.
If you really need that much Speed/Performance you should be looking at a bigger bike.
 
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