Topic: 500/4 conrods

[Colin Tweedie]

I am starting to build a spare engine for my 500/4 race bike  . I have 4 old engines of which I hope to build two goodish engines on the cheap using mostly standard parts. ( no money till I sell my Tab k4 ) got one stripped ,sand blasted and ready to put together with a rebore and  new cg125 pistons . Big end and crank shells all look good so save some dosh their . Thought I would have a go at lightening and polishing the rods removed 24 grams from them by removing cast marks etc and polishing , pictures show from left to right old rod ground rod and finished rod. Question is have I over done it will the rod fail under load , any ideas tips would be great . should I just fit the standard rods or save up and pay Stockers an obscene amount of money for trick ones ?

[Greggo]

Subscribed.  I'd like to hear what the more experienced guys have to say.

[MRieck]

You should have just polished the beams and shotpeened the pieces. Also...use 750 F2 rod bolts and nuts. 24 grams is a lot to take off a small rod. Please don't ask me if they will fail....I do not know....that's your call.

[Doctor_D]

You should have just polished the beams and shotpeened the pieces. Also...use 750 F2 rod bolts and nuts. 24 grams is a lot to take off a small rod. Please don't ask me if they will fail....I do not know....that's your call.

+1

Also, please pay attention to the big end and small end weights as you remove material.  (My CB750 rods are balanced, cryo'd, polished, shotpeened, and use F2 bolts. I'll let you know if they break.)

[fastbroshi]

I was talking with an old guy that used to DRAG a hopped up 550, he said he used the stock rods and just shot peened them.  He said he made many runs revving up to 10K RPM on the regular and never had a failure. 

[turboguzzi]

gee, dont want to even think how much time you've spent doing that...

the stock rods on my 500 racer, no shot peening, no special bolts, no nothing, held for four season with plenty of forays to 12K-13K rpm, bet they are ready for more

unlike 750's, 500 rods are quite over engineered.

I think that the only way to find out if they'll fail is to use them and see

[lordmoonpie]

Sounds like a lot of weight removed to me - I polished my 250-4 rods and took 2.5 grams off each. I know it's not as simple as doubling up but 12 grams sure sounds a lot. It also depends on your intended use. For old Honda engines destined for the IOM, use stock rods and stock crank unless you want to pay for fancy rods like Arrows in which case you'll get a benefit. If it's short circuit stuff you might get away with it for some time but as everyone says, if it's a race motor the only way you'll know if to try and find out.

BTW if you go down the fancy rods route, I can utterly recommend Arrow. Their products are awesome and the design dept is really really helpful in specifiying exactly what you want and need. But then I only used them in my 750, I have no 500 experience...

[Rod]

as others have said above - no need to do more than polish / peen - with the poor aspiration on the 500 head you'll run out of useful revs before the rods give up.