Timing Chain, 72 link Part # 92057-1019 C25H Roller Chain 72 link

I've spent almost a week trying to source a new Timing Chain 72 link  part # 92057-1019, used on all model years as near as I can tell. The final outcome of this post will be what I found as a reasonable replacement for this No Longer Available Chain.

MCG in Germany www.z1300.de sells a replacement for this chain but it's not an identical replacement, meaning in the engineering world a reasonable replacement needs to conform to the 3 F's, Fit Form and Function. The MCG chain meets the Fit and most of the Function but definitely not the Form Because of not being able to meet the 3 F's, I have concerns about using this chain. 

 

This is a pic of the old chain (lower chain with oval side plates) and a similar replacement  (upper chain with figure 8 side plate) like the one available from MCG. Also shown is the tensioner guide shoe that the chain is tensioned with.

Regarding the "Fit"  and "Function"-
The original stock chain is a #25 chain with 72 links and has what's called in the chain world either "Flat Sidebars" or Straight Sidebar Links" meaning the links of the chain are oval in shape instead of the standard roller chain figure 8 shape. Why is this important? The flat side of link rides on the tensioner guide which is a plastic based guide shoe. It could be Nylon 6/6 or maybe another form of nylon. A 72 link #25 chain is the right size and my only concern is that a standard #25 roller chain as made available from MCCG being a figure 8 link plate style will have the chain bearing on the guide on 2 spots of each link rather than bearing on the entire side of each link. My concern is not if the chain will last, but if the tension guide shoe will wear out prematurely.

 
Stamped 25H and remember the space between the pins is .250" or 6.37mm so you can imagine how small the letters are.

 

On another post under my topic " Kawboy's Restoration" Stocktoy asked me if the chain had any stampings on it and my initial response was No. Today, after trying to figure out what the industry would call this chain, I decided to seek out an expert's advice. I ended up at Motion Canada and talked to one of their sales people and after looking at the chain for 10 seconds  says, "Well, it looks like a C25H chain. It's stamped 25H. Let me call my supplier" So Off he goes to his desk and makes a call. He comes back to the counter and tells me if it was a C25 chain, he has it in Cambridge Ontario but this is a C25H meaning heavy duty and he has to check with a couple of suppliers and will get back to me. So I take the chain with me and head home.
When I get back, I look at the chain again and I can't see "25H" stamped on a link. So, I grab my smartphone and open up the camera function and dial it up to 8 times magnification and sure enough, some links are stamped "Japan" and some are stamped 25H. Go figure !!

Another hour on the internet looking up a C25H roller chain and yes, C25H definitely describes the appropriate part #. So now I just need to find a reputable manufacturer . We'll see what my supplier comes up with

 

The drawing of this company's 25H chain suggests that it has straight side plates. Would it be worth asking if they have a distributor near you? Maybe you've already tried them.
www.durochains.com/durochain-premium-25h...chain-p/rc-p-25h.htm

Nice find there Jim !! I'll keep it in mind if my supplier here fails to locate a source. He's already invested time in this so he should be rewarded with a sale if possible.

Just thinking outside the box a little.....

If the chain guide is curved..... then only the centres of individual 'oval' side links touch the guide, while on a figure 8 chain, both ends of individual side links touch the guide - perhaps doubling the contact area?  I guess it would boil down to how much of the centre link touches the guide vs how much end links touch the guide.

Bucko wrote:

Just thinking outside the box a little.....

If the chain guide is curved..... then only the centres of individual 'oval' side links touch the guide, while on a figure 8 chain, both ends of individual side links touch the guide - perhaps doubling the contact area?  I guess it would boil down to how much of the centre link touches the guide vs how much end links touch the guide.

Valid point and thanks for bringing it up. Maybe the figure 8 chain would give more contact support per link than the flat side chain? Interesting....... Very interesting.

Thinking this through-
If a flat sidebar link ( oval shaped link) contacts a round surface guide, then the center of the link would only contact the guide which is 1 contact per link or 1 contact per pitch.
A standard roller chain with a figure 8 link plate would contact the guide over the center of each roller which is also once per pitch so -
The contact is equal no matter which chain type is selected - one contact point per pitch.

So glad to have this forum to discuss things like this and provoke thought. Here I was thinking that the MCG chain option could be a problem and I was swaying away from it but now thinking that it's a nonissue. this would open up many more replacement chain options provided that the chain is a 25H series (heavy duty) as opposed to a standard 25 series chain.

I'm not an engineer but in a previous life, had a great deal of exposure to engineering and it's affected the way I look at problems. At least I don't barrel ahead and just replace things without any thought process.
Thanks to all those who participate in these discussions.

Wouldn’t it be interesting to speak to the engineers who designed this engine? What was the thinking behind opting for the straight side plate chain? Also, why did they think it was acceptable to have the valve timing influenced by primary chain wear?