Early CB1E conrod vs SC03


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LONGCLOSE
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Early CB1E conrod vs SC03

Post by LONGCLOSE »

Hi everyone,

I am currently in the throws of the final assembly of my CB1E motor. I have been advised by the local CBX guru here that I should fit the later 422 conrod from the SC03 engine rather than the 11S conrod which were the originals. The trouble is that this will leave me short of 422 conrods for my next rebuild on an SC03 motor which I have.

I have weighed the two rods and the 11S conrod is 10 grams lighter than the 422. The reason I was told to use the later conrods as they are stronger, I am fitting 1123 piston kit so the engine will be slightly higher stressed than stock, compression I have calculated about 10.2:1.

The bike will be to original spec. and will not be ridden hard so I appreciate any input to my question.

Thanks to you all in advance..

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Re: Early CB1E conrod vs SC03

Post by EMS »

Never heard of a "115" connecting rod. If this number indicates the product code, the part would come from a 50cc motor (CB50).
Wonder who that CBX guru was, you talked to :?
At least Honda lists all conrods for the CB1E being the same as for the SC03E. "422" part numbers.

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Re: Early CB1E conrod vs SC03

Post by daves79x »

Honda CBX rods were made in batches, with different marking numbers, but the metallurgy is all the same. The weight code tells you what it should weigh and you should match up codes. Most engines are 'B' code or 'C' code rods. Weight within the same rod codes should be within 2 or 3 grams of each other in any given engine. Although we have found this not to always be the case. Better find a different CBX 'Guru'.

Dave

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Re: Early CB1E conrod vs SC03

Post by LONGCLOSE »

Thank you all for the feedback,

I assure you they are visually different, have posted a picture, they were removed by myself from the original CB1E engine, the six S11 conrods weighs 339 grams the 422 rod 349 grams - 10 grams less.

The CBX Guru restores,rebuilds and maintains CBX's probably running into the 100's in the last 20 years, there is at least 5 bikes in his workshop at any one time, he has owned his original prolink since 1983.

He recognised the S11 rods straight away and recommended moving to the 422 rods as they are more resilient to over revving, Visually the 422 has a slightly thicker web. I am aware of the weight codes but 10 grams I would have thought would be well outside normal specification and must be a different early design and could not be matched with that weight difference?

Maybe it is just the batch code but these two batches could never be matched at that weight difference surely...
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Re: Early CB1E conrod vs SC03

Post by EMS »

What is your original CB1E engine serial number?

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Re: Early CB1E conrod vs SC03

Post by LONGCLOSE »

Hi EMS

The engine number is 2024615, I think Dave may be right as the part number are the same for the CB1 and SC03 motors. It appears that the 422 conrods came along later, still amazed that there is a 10 gram difference, unfortunately due to age and storage the weight values are difficult to determine hence the need to weigh them!

The Guy ins SA says he has never seen a 422 rod thrown through abuse but has replaced (or seen blown motors) on many of the "s" series rods thrown on the CB1E motors so its just from time and his 30 years of personal experience not from engineering prowess in metallurgy!

Anyway I think I am safe with the S11 rods as I do not intend to abuse the said restoration!!!

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Re: Early CB1E conrod vs SC03

Post by EMS »

Your engine is one of the last ones built for the CB1 and most likely dates into January or February of 1979. Hard to believe that the "422" rods came along "later"

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Re: Early CB1E conrod vs SC03

Post by LONGCLOSE »

As I said he strips and rebuilds CBX's across South Africa as his daily job and has done for 20 years, he referred to the 422 conrod as being from the "B" motor or SC03, he must have at least 10 stripped motors in his store room as I have seen the crankcases. The part number for the CB1E engine and SC03 is the same on CMSNL site so it would be good if nothing else to understand if the rods are interchangeable for future rebuild projects as rods are now becoming pretty scarce second hand.

I will try and see if I can identify the weight codes on both sets and do a comparison and feed back, maybe others could take a look from their stock as 10 grams between the two rods is 3% difference and would destroy a finally balanced engine in no time. I found this link which Dave 79 commented on, may this indicates that they are incompatible viewtopic.php?f=25&t=10322&start=0 The outcome was unfortunately never published.

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Re: Early CB1E conrod vs SC03

Post by daves79x »

There is at least a 10 gram difference between weight codes. That's why they are coded. 422 is a '79 first-year part number. As far as any other year's rods being more robust, I've seen bent rods from hydrolock on every year CBX. And several late models with spun #6 rod bearings. They may look slightly different, but in service they are not. Match your weight codes and double-check by weighing them.

Dave

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Re: Early CB1E conrod vs SC03

Post by EMS »

If the rods would have been new and different for 1980 (SC03E) they would have a -469- instead of a -422- part number. That's how the Honda system worked and still works. No reason to doubt it was different for the CBX

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Re: Early CB1E conrod vs SC03

Post by LONGCLOSE »

Thanks guys, am learning the intricacies of the CBX idiosyncrasies as I go. All the six (s11) rods were within 1 gram, so ready to go on installation, I am also rebuilding two Cb1100RC engines and noted that the conrods were 7 grams difference between the codes so Dave you are right. I am now not worried about throwing a rod!

Thank you so much for the advice and feedback, will get some pictures published of the restored 79 "black" CBX when finished engine as currently stands..
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Re: Early CB1E conrod vs SC03

Post by EMS »

If it gives you additional assurance and peace of mind: I think the "S15" is a forging code and does not contain any reference to weight or any other spec of the conrods. I checked my parts stash of new and used rods and I have a plethora of different markings, S1, S2, S10, S14, S15, S16, S18, some with and some without the "422". There are minor differences in appearance but again, it probably depends on what forge they came from.

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Re: Early CB1E conrod vs SC03

Post by LONGCLOSE »

Certainly re-assured, the 40 years of the engineer in me always questioned the statements that were made about the rods, the guy certainly knows his stuff but in this instance I think it is purely a misconception. It is just pure chance the rods he has seen thrown (not bent by locking) were the "S" series.

One more problem down now just need to deal with the fact that I need 315 shims (which don't exist as stock!) for 3 inlet valves on a rebuilt ported head which came with the package of parts I acquired. Looks like the valve stems are short so need to pop out and replace tomorrow.

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Re: Early CB1E conrod vs SC03

Post by EMS »

LONGCLOSE wrote: One more problem down now just need to deal with the fact that I need 315 shims (which don't exist as stock!) .
They do too. Part-No 14935-422-000 from Honda. Same diameter shim was also used by Yamaha and by some car manufacturers. Just search for 25mm shim.
Honda shims were available up to 3.50.

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Re: Early CB1E conrod vs SC03

Post by LONGCLOSE »

Thanks EMS it is good to know, I just searched my stock and a brief trawl of the web.

Under the circumstances I am going to investigate further as all other shims up to journal 12 are 285 to 295. Journal 13 to 16 are 305 to 315 with the valve stem not protruding above the collets (visually at the moment) on the 315 measured shims.

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