My 750 K6 was Modified to 838cc and worked very well , later a 970cc Russ Collins set was installed - that was not so good , it had very high compression and the starter motor could not start it so all in all it did not work so well.
@@SPANNERRASH Yes , the trouble was that R.C Enginerings sets originally was intended for drag racing so the compression was way over 11,5 to 1 and in fact would have broken the conection rods quickly , it one of the 750 honda engines weak points - just to tell that R.C also had a 1015 cc set and also a set with stroker conection rods for the Honda CB 750 engine but yes it was a huge remoddeling of the crane case and New chromemolybden cylinder liners and when the Cylinders get so large diameter that the problem with the oil channels really is apparently , the first time my engine was started back then at the mc-shop it spilled oil out all the wrong places but got fixed but ended up breaking the piston - rings in one cylinder which cooked the oil and nearly seized the whole engine and i had to give it up returning with another 750 engine bored to 838cc and a Modified cam and greater exhaust valve , it worked well for many years . Sure miss my 750 Honda (in blue k6) Every spring thinking riding in the sun.
To be honest I am not sure. If you watch the video again around the 5 minute section the bottom of the barrels where the oil drain comes through is different. If one of these oil passage ways through the barrel is blocked where it joins the crankcase is blocked off then it will stop oil draining properly from the head. You will need to check your crankcases to see if this would be an issue. If you look at video no 19 in the playlist for this bike around minute 11 it looks like my engine does have the right openings on the crankcase, but I don't know if this is true for all later engines. Good luck.
I'm about half way through this series now and I have to say they are amongst the most informative restoration videos I have found. Much appreciate not just the info but the time it takes to film and edit. I am currently looking for a rebuild project and I am pretty much decided on a CB750 SOHC. Looking forward to getting caught up and seeing how the first ride goes.
Wow, thanks! CB750's make great projects, and even better bikes to ride when you have done them, so it is a good choice. Hope you enjoy ther rest of the vids as we put them out.
I'm glad my video helped. I suspect that your heads would both be ..300.. part numbers. Although they added those seal cut outs they didn't change the part number much, and I do think they are interchangeable.
@@ALA-uv7jq I'm not sure what you mean by oil control jets. The all have one oil control jet for each cam block. But there is only one drain per side on the later head.
Hi. Thanks for the info decrypting the differences between the barrels and head. I have a 1977 CB750 and was just going to swap the K series head with a F series because of the bigger valves. Now I will take a much closer look at what I have. Thank you!
@@SPANNERRASH Thank you. Yes that makes sense on the compression, larger chamber lower compression. Do you know if the F series head intake and exhaust ports flow any better than the K series head? Thx!
@@timmyc7898 I suspect that with the bigger valves if will flow better. The F head also has revised cams that I believe open quicker and stay open longer, but the there may not be a lot in it. I also believe that this causes earlier issues with the guides wearing. Unless you are really chasing every last little percent of power I don't think it would be worth the cost. Good luck with whatever you decide.
Thank you, all good info. Looking for simple power upgrades and thought the head swap might be a good one. I need to disassemble the engine this winter and replace the primary chain, it’s shot and makes a lot of noise. The tensioner is maxed out and it still has a lot of slack. Thx and keep the videos coming!
@timmyc7898Do NOT use a 410 head [F2] with a k series cylinder ....totally incompatible, ...... yes it will physically fit .... BUT you get massive oil leakage from the cylinder fins.
Very informative and interesting video thank you for sharing
Glad you enjoyed it. I'm finding out more and more about my engine.
My 750 K6 was Modified to 838cc and worked very well , later a 970cc Russ Collins set was installed - that was not so good , it had very high compression and the starter motor could not start it so all in all it did not work so well.
It's amazing that the old SOHC could be taken out so far. It must have been and expensive build, with a modified crank as well.
@@SPANNERRASH Yes , the trouble was that R.C Enginerings sets originally was intended for drag racing so the compression was way over 11,5 to 1 and in fact would have broken the conection rods quickly , it one of the 750 honda engines weak points - just to tell that R.C also had a 1015 cc set and also a set with stroker conection rods for the Honda CB 750 engine but yes it was a huge remoddeling of the crane case and New chromemolybden cylinder liners and when the Cylinders get so large diameter that the problem with the oil channels really is apparently , the first time my engine was started back then at the mc-shop it spilled oil out all the wrong places but got fixed but ended up breaking the piston - rings in one cylinder which cooked the oil and nearly seized the whole engine and i had to give it up returning with another 750 engine bored to 838cc and a Modified cam and greater exhaust valve , it worked well for many years . Sure miss my 750 Honda (in blue k6) Every spring thinking riding in the sun.
@@oleriis-vestergaard6844 Great to experience the different builds, but at the end of the day reliabilty gets you riding in the sun more often. :)
RATHER INFORMATIVE ,,THANK YOU !
Glad it was helpful! I just hope it right. It is difficult to find solid information, it is one of the reasons I made this video.
Good info.... I have 3 motors to make one.
I am really pleased if it helps. It is really hard to sift through the information on forums, I am sure some people just make it up :)
What about an k series head with F series cylinders?
To be honest I am not sure. If you watch the video again around the 5 minute section the bottom of the barrels where the oil drain comes through is different. If one of these oil passage ways through the barrel is blocked where it joins the crankcase is blocked off then it will stop oil draining properly from the head. You will need to check your crankcases to see if this would be an issue. If you look at video no 19 in the playlist for this bike around minute 11 it looks like my engine does have the right openings on the crankcase, but I don't know if this is true for all later engines. Good luck.
@@SPANNERRASH thank you!
I'm about half way through this series now and I have to say they are amongst the most informative restoration videos I have found. Much appreciate not just the info but the time it takes to film and edit. I am currently looking for a rebuild project and I am pretty much decided on a CB750 SOHC. Looking forward to getting caught up and seeing how the first ride goes.
Wow, thanks! CB750's make great projects, and even better bikes to ride when you have done them, so it is a good choice. Hope you enjoy ther rest of the vids as we put them out.
Very helpful explaining the diff heads. I have two heads with no numbers, but seems from your vid that one is a 300 and one is 392.
I'm glad my video helped. I suspect that your heads would both be ..300.. part numbers. Although they added those seal cut outs they didn't change the part number much, and I do think they are interchangeable.
@@SPANNERRASH Also interesting is one head has the double oil control jets. Are these important as they dont appear in the early heads.
@@ALA-uv7jq I'm not sure what you mean by oil control jets. The all have one oil control jet for each cam block. But there is only one drain per side on the later head.
Been really enjoying this series especially as I’m looking at starting a cafe racer project it’s been very helpful thank 😊
I'm glad you are enjoying it. I must pick up the pace a little now the sun is out :)
Nice Hitchhikers Guide reference. Is this for the cafe 750 project you picked up? It seemed like you got a good deal on that one.
I love Douglas Adams' books! This is for the Cafe Project. It's taking longer than I thought it would, but I am still thrilled with gettting it.
Hi. Thanks for the info decrypting the differences between the barrels and head. I have a 1977 CB750 and was just going to swap the K series head with a F series because of the bigger valves. Now I will take a much closer look at what I have. Thank you!
Glad it helps. I think what you are suggesting would work. The oil ways through the barrel would be fine, but you would lose a little compression.
@@SPANNERRASH Thank you. Yes that makes sense on the compression, larger chamber lower compression. Do you know if the F series head intake and exhaust ports flow any better than the K series head? Thx!
@@timmyc7898 I suspect that with the bigger valves if will flow better. The F head also has revised cams that I believe open quicker and stay open longer, but the there may not be a lot in it. I also believe that this causes earlier issues with the guides wearing. Unless you are really chasing every last little percent of power I don't think it would be worth the cost. Good luck with whatever you decide.
Thank you, all good info. Looking for simple power upgrades and thought the head swap might be a good one. I need to disassemble the engine this winter and replace the primary chain, it’s shot and makes a lot of noise. The tensioner is maxed out and it still has a lot of slack. Thx and keep the videos coming!
@timmyc7898Do NOT use a 410 head [F2] with a k series cylinder ....totally incompatible, ...... yes it will physically fit .... BUT you get massive oil leakage from the cylinder fins.