Hi,
Vince, thanks for the info, but do they make cams, or do they remake cams ?
My experiences with the standard cams are good, especially the early ones, the reason that the CB72 gets asthma in the high regions (is this good English ?) is that the exhaust port becomes too narrow for the volume of gases it has to let go, there's just too much pressure building up that effects the mixture refreshing in the combustion chamber in a negative way.
There are two ways to solve that problem, first one is another camshaft profile which opens the exhaust valve earlier and closes later. The other way is to redistrict the exhaust channel. Both methods can be combined. I choose for the second way, because it doesn't involve all kind of exotic parts. Both methods have there impact in the low regions and on the low midrange where the needle takes over the stationary jetting.
This is one of the reasons to change the carbs. Not that the CB72 carb isn't good enough in a standard trim, but it is simple (and that's not a negative statement) but because of that not sophisticated enough to adjust to the new situation.
Loud Mouse, what kind of compression ratio do you suggest ? In the sixties and seventies the main idea was the higher the better, until the petrol would give up and had a premature combustion. Maybe that a little exaggerated but I understood this from a lot of tuning specialists in those days.
Today the patrols are more stable, and if I have to use high octane petrol so be it.
I do have a choice here, standard pistons, standard high compression pistons (early piston's), after market pistons. I will make the pistons lighter, and I'm able to change the piston floor to have the squish area I want (I'll take a modern piston as an example).
G-man, I 'll come back to you soon,
Again, thanks for all inputs,
Jensen
30 HP out of an CB72 ?Jensen
Also - check out http://www.eurospares.com/cr216.htm There is a tuning manual for the CB160 which may have some tips (7th paragraph) G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F
Hi G-man,
Like I said, I won't play with my guides, Honda made them good enough to deliver 30HP out of this engine. The cast iron guides are doing there job excellent, it rarely goes wrong there. Phosphor bronze is a good alternative, but if I wanted to change the guides I would go for titanium valves, the prices of these valves are not so high anymore. Until it is necessary to squeeze the last HP out of the engine I'll go that way. I'm a "little" perky about this, maybe time will learn. About flowing. Yes I have my own stuff to measure, and please don't laugh, a regulated vacuum cleaner, a few manometers, a piece of rubber or silicon and you're in business. But...... this I only use to be sure both sides have the same flow resistance. Real advantages are the lessons learned from others how (most of the time) not to do it. There's one thing to keep in mind, the bore * stroke is 54 * 54 mm, and that's square. A few years ago I started to look at other square engines, especially how the inlet and exhaust where shaped. Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
I think there are 3 different HONDA issue compression ratios for the 250 I and just wondered which ya are considering. ................lm
Loud Mouse, what kind of compression ratio do you suggest ? In the sixties and seventies the main idea was the higher the better, until the petrol would give up and had a premature combustion. Maybe that a little exaggerated but I understood this from a lot of tuning specialists in those days.
Jensen -- Phil Joy remachines cams, regrinds, can adjust the profiles, etc, and his particular specialty is Hondas. I can't really tell if he makes them from scratch -- Classic Bike Magazine did a two page article on him in April 2009, and I had heard of him before. He seems to be the top camshaft expert in the UK, and I think his shop in Hertfordshire might be a one-man operation.
Somewhat off topic from this thread, but I thought this was an interesting quote from him in the Classic Bike article: "Riders often misunderstand how cams should be looked after. Most engines last longer when they're worked fairly hard. A slow-spinning cam will suffer a lot more stress than a fast moving one; faster movement prevents the cam from being scuffed so much, and more oil gets splashed around. If a bike has been laid up it's best to get some oil on the camshaft and other parts before firing the engine. Otherwise, start the bike and set it running at a fast idle. That's the best way to get oil pressure up." I thought that quote was interesting, and wondered if it could also apply to breaking in a freshly rebuilt engine. Not necessarily redlining it right off the bat, but not babying it either. Here is another quote from the article: "Most Japanese camshafts are cast steel with welded-on stellite faces. Cam followers sometimes have stellite facing. Honda CB72 and 77 models had a chrome face. This can be replaced with stellite -- it's harder-wearing and doesn't flake. The followers on higher-lift cams don't usually need to be re-radiused. When measuring cam duration I measure from 1mm valve lift. Manufacturers quote varying amounts which can be confusing." Hope this helps you somewhat....
Hi LoudMouse,
For the moment I'll go for a compression ratio 10.5:1 unless someone has good experiences with higher or lower ratio's. I know that there are three types of pistons, 268-000, 268-010 and 268-030. I have the 010 and the 030 versions available, but not the 000 version. Actually I've never seen one in real live. What are the differences with the 010 version ? You talk about 3 different pistons, but are you pointing to these three ? or is the third a dream piston ? I do have a few strange pistons with 2 rings (1 compression ring and 1 oil ring), and I have one set with four rings, both without part numbers. I brought these pistons (and a lot of others) for verification to a specialist John Schermer-Voest (in memoriam), and he said that both where used for C's and CB's. John past away in December 2009, and with him a lot of knowledge. He raced several years with these bikes, also with a CR77 I spent a lot of long evenings with him talking about these machines and I acquired a lot of first hand information from him. But after he passed away, I realized how much information and anecdotes are lost for ever. http://www.kjmv.nl/artikelen/John%20Sch ... 0Voest.pdf Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
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