dommie vs commando rods

I have taken the Manxman...sorry, 650 SS...motor apart. All looks good except the crank journals need to be turned. Question now ...for the average rider...is it worthwhile to replace original rods with commando rods? I've heard they are stronger. Both are available to me at no extra cost. The crank will be balanced to 64% afterwards.

Also, can you recommend anything else to improve the motor? Original cam looks very good. Anything in the head besides bronze guides and modern valves? I would love to use the JS rods and pistons but it is not my motor or my money.

Jim Scmidt and I consulted 10-15 years ago about the piston weight/balance parallel twin vibration problem. I whole heartily concur with the weigh loss program and am a big proponent of it. However, I am not rich enough to go beyond aggressive weight saving attempts off standard components, pistons, wrist pins and small end of the rod. This will be one of the most worked on areas of my next build of my 65 engine, the "2S combat" cam hot rod atlas. There is no weight saving to stay with the R1 or R2 early rods. The R7 (combat era) or R8 (850 era) are within 3 grams of each other. 388-391 (no shells) So if you believe the rumors of "stronger" then go with it. I'm keeping my early rods for the 650 and the later ones for the 10.5-11 CR pistons in the 2S atlas. It have a good (no spigot) atlas head that was previously drilled for 3/8 head bolts, so I'm using commando barrels. I will give it a clone porting job identical to my 1992 rally commando head...awsome...28.5mm port plus working all around the guide and short port to the seats
Another thing I'd suggest, which I am doing , is very close attention to the advance curve. Get away from the mag with a stone age AA curve (none). get a commando type rear distributor lucas or ? norvil or other. for a good EI advance curve. I don't have any data yet but it might not be the same for the 650ss. To start I'll use a rita.... then try something programable
DON'T use the stupid manxman/650SS intake rocker cover vent. I can't believe people buy into it?
My 2 cents

Thanks...I was talking to JS about the Commando rods being stronger than the earlier ones and he said there was more metal at the top of the commando rod so that would make the small end a bit stronger. My big questions the length. ARE THE TWO RODS INTERCHANGEABLE?
Or...if mildly ridden will the original 650 rods be sufficient? Should I just get the originals resized and be happy?

I would like to replace the magneto with a pazon ignition and, as you said, get a real advance curve. However, the owner really wants the mag and has sent it off for a complete refurbishing. So that is what we shall use.

A question for Dynodave, whats the issue with the inlet cover breather?, I can see that its not going to be a effective as a proper case breather,but might be helpfull in stemming leaks from rocker bolts and covers. With regard to rod breakages ,I've never had any and consider that its more likely that these are down to bad workmanship ,poor timing and tune . There is also the added factor that in the UK we don't use the machines the same way as the US. Bikes have always been thought of as valued transport and treated with consideration. I still use a classic in preferance to cars ,van or truck which are all ready to go.

seattle##gs " ARE THE TWO RODS INTERCHANGEABLE? "

yes interchangeable, I would agree the shape of the front/rear arc inside the web area below the wrist pin area is more gradual than the early rods to spread out stress loading. Same at the bottom.
For a bike not abused like a race bike, I don't see the need to replace them.

I would have replaced the Lucas maggie with a moden Joe Hunt, a lot better in the long run, my Manxman has a Lucas compertitison maggie on it which is better than the standard maggie but if it plays up a JH will replace it, my hot 850 works so well with the JH, but of course thats my opinion, I would never go back to anything else.

Ashley

The early 650 series had a few 'features' which weren't so robust.

Weren't the rods one of the things that were improved not very far down the road. ?

dynodave said:

It have a good (no spigot) atlas head ......

Click to expand...

Hi, it means that the spigot head is not good?
Thank you.
Piero

pierodn said:

dynodave said:

It have a good (no spigot) atlas head ......

Click to expand...

Hi, it means that the spigot head is not good?
Thank you.
Piero

Click to expand...

Sorry english does not always give precise meaning:

I have a good atlas head.

what kind of head ? (no spigot) or flat barrel
Dave

Why have spigotted heads leapt into a conrod discussion - enquiring minds and all that... ?