Honda Twins banner

1 - 20 of 40 Posts

·
Registered
Joined
·
18 Posts
Discussion Starter · #1 ·
Hello all,

So I bought a 74 cb450. I ended up tearing apart the motor after finding a bad oil leak. After measuring the pistons, I'm having a hard time sourcing new rings. Stock pistons are supposed to be 70mm, but mine measure at 73mm. The biggest oversize kits I can find are 71mm. Can anybody help me source new rings? I accidentally broke an oil ring so I'm kind of screwed if I can find a new set.
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #9 ·
Does the -12 indicate amount of oversize? This piston has 450-12 stamped on the inside. I wasn't quite sure what it means.

Also what is ring mfg.s?
 

·
Registered
Joined
·
13,085 Posts
The term is S-12, as in 12 sizes over stock going in 0.25mm increments totaling 3mm in your case. It's usually done to increase performance, as more CCs equals more power. My comment on the ring lands refers to the ring and piston manufacturer being the same, as in the thickness of the ring and whether or not it will fit your pistons. They aren't always the same when from different manufacturers. His comment was an abbreviation for "ring manufacturers"
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #11 ·
Hi friends, so I finally received the the rings mentioned above. After test fitting in the cylinder they appear to still be too small. The ring end Gap meaures about 2.5mm. So it seems like I have two options here.

First option is to reuse all of my old rings. I would only use one of the oil scraper rings (I broke the original one). Would this be a bad idea?

The second option is to try to find a 4mm oversized ring. I did a quick Google search and couldn't find anything, but I'm sure they exist.

Any opinions would be greatly appreciated. I attached a picture with one of the new rings in one cylinder and one of the old rings in the other.
 

Attachments

·
Registered
Joined
·
13,085 Posts
I had my doubts about that listing after re-reading the way it was written a few times. I think the seller was describing them in a way that made it sound like 3mm oversize but didn't actually mean that... judging from the huge end gap, I'd say they aren't very oversized at all, unfortunately. It's not going to be that easy to find a set of 3mm over rings, I've been looking for a set of 4mm over rings for my bike and only the handful of high-performance piston sellers will have them and again, they might not be a correct fit for the pistons you have depending on the manufacturer. Todd Henning Racing and M3 Racing are the only commonly-known names I'm aware of now that Terry Naughtin of Team Hansen has fully retired (where I got my 74mm pistons), other than trying the piston manufacturers themselves - Wiseco being the most well-known in the motorcycle area. Here's a possibility - but you should call and talk to someone about it, however, at least this listing has the thickness measurements for the rings to compare to yours

https://www.z1enterprises.com/piston-ring-set-730mm-z1-kz100044-gs1000.html
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #13 ·
These are significantly bigger than the stock size rings. The stock rings I bought just fell right through the cylinder. I'm starting to wonder if I need 74mm rings.

The real question is, how bad would it be to use one of these new rings on the oil scraper and then just reuse my old rings for the compression seals?

Would it significantly affect compression? I'd really just like to get this thing back together for the season. If need be I can do a more thorough tear down this winter.
 

·
Registered
Joined
·
641 Posts
You will need to check that oil ring for fit in piston groove. Also you will loose some compression, how much i dont know. That would be the risk of doing all that work. And it not performing well, then again it might. Thats a choice to make, check cross section of ring too. Just look at the end of the broken oil ring, and compare it to the new one.
You could take pics of all three original ring ends, to email a ring manufacturer to see if they have them too.

Sent from my SM-N920R4 using Tapatalk
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #15 ·
Hmm... That's kind of what I figured.

I think these rings might be more work than it's worth. The pistons themselves are a little worn out. So I'm going to try and find a stock sized cylinder and just bore it out to the first size. This way I can have fresh pistons and rings.

For the mean time I'm going to try putting the motor back together with the rings I have. I don't have high hopes, but what have I got to loose?

Any suggestions where to source the new cylinder and pistons? Right now I'm looking at this set on ebay.

Cj0KCQjwocPnBRDFARIsAJJcf95S9sxL1IgFeHf82gKAgdD6p6PqXOr9lMdFntL2qHS35O5wANM_FuYaAqBnEALw_wcB
 

·
Premium Member
Joined
·
5,550 Posts
Oil rings don't really count for compression as long as you didn't break any of actual compression rings I would just run it. I'm with TOOLS it may just burn a little more oil on that side it may not, that is, IF you can get that one back on the piston without breaking it as well. As long as the compression is good on both sides and you get good oiling I would not even worry about scoring on the pistons, maybe polish it a little if you can catch the grooves with a finger nail.

SIDE NOTE if it is overbored the top of the piston SHOULD be stamped with the overbore, if they were at least GOOD pistons.
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #19 ·
Thanks guys! That's exactly what I've been thinking, but all the car guys at work have been lecturing me about not cutting corners on a motor rebuild. It's nice to hear that I'm not crazy about this.

The pistons were stamped on the underside of the skirt. It has a 450-12 which one of you guys said means it was bored 12 sizes over.

I'll look into that ring mfg site, but I think if the motor comes apart again I'm just going to drop the money on some quality machine work and a new cylinder.

I'm going to try and get the motor back in this weekend. I'll keep you guys posted. Hopefully I can wrap up this project and get back to my RD350. These four strokes are getting too complicated for me ?
 

·
Registered
Joined
·
13,085 Posts
The pistons were stamped on the underside of the skirt. It has a 450-12 which one of you guys said means it was bored 12 sizes over.
Just to be clear, I explained the term S-12 and what it means with reference to overbore pistons and rings... I didn't say that what is stamped on your piston meant it was 12 sizes over, although it would certainly allow for the assumption
 
1 - 20 of 40 Posts
Top