Topic: 550 vs 500 head

[hymodyne]

Evening,

are the valves and porting the same on the following cylinder heads: a '72 500 and a '76 550?

Hymodyne

[neckyzips]

funny, i was just going to ask that percise question! why do you want to know?

[hymodyne]

I'm asking because I bolted a head from a '76 550 onto my '72 500 jug, using my 500 cam, chain and valve cover.
it bolted up perfectly, but a gentleman raised the question about valve size and porting last evening and I began to wonder if those differences would have anything to do with the difficulty I'm having tuning the bike in...It starts right up, idles at approx 1100, and I only have to use the choke when its first starting. when I put it in first and try to roll off,  the engine bogs down, I have to rev or keep the throttle at 0ver 3000 rpm to get forward motion without stalling. I was having some problems with a cold cylinder (#4), but as of last evening, all four are firing. A honda mechanic suggested a compression test, believing that poorly seating valves or ring issues might be causing my problem. as of yet, I haven't been able to find a compression tester that is made for motorbikes around here at all,(NW Mass),  or online that doesn't cost an arm and a leg.

hymodyne

[neckyzips]

just asking, but why  did you put a 550 head on the 500? it does sound like rings, at least to me i would think if it were a head problem. it wouldnt want to sit and idle. unless the 500 cam is ground differently and doesnt open the valves enough on the 550, have you checked your valves, ie adjusted the tappets?

[hymodyne]

I used the 550 head becuase that is what I had in my garage. I had looked at older greenspun archive threads about this and read one where someone confirmed that a 500 head could go on a 550 jug. I'll check the specs on valves for the 550 and see if any adjustments should be made


hymodyne

[neckyzips]

the reason i ask,
i just ended up with 600cc jugs, and figured that the 550 head ports, and valves may be a bit larger?
but i do have a 500 head if  you need one trade..