Topic: Engine rebuild then find a frame

[Wingnut74]

I spent last winter rebuilding a cb750k4 engine last winter that was rust seized with all new oem+1mm pistons, and rings, MReick valve job, mild porting and it was super fun. So fun  that I wan't to do it again.It runs awesome!  Also to boot I never rode anything bigger than a CB400 until I rode my 74 cb750, and holy crap does it have some pull! So I have been looking for a new winter project looking at hundreds of bikes and specs and have come to the conclusion that our old bikes were not only awesome in their day, but still are wildly better than some new bikes  like a brand new Harley Sportster (a 2001 883 CC  -Sportser has the advantage of 25 years of technology and more cc's and can only manage 50 HP- that is disgraceful). And a 2001 bmw 1200c has only 61hp, Or if you look at an old Beemer airhead you have to go to 1000cc to get to what a cb750 can do. So you all probably knew all this, but I am amazed at how superior the CB750 is. So my next one is going to be another CB750, but since I am so enjoying the extra oomph, I want to go for higher performance on the next one and learn more stuff.

 I have not been able to find a cheap bike with an engine to rebuild, but I see cb750 engines that I just want to buy, rebuild over the winter and then find a titled frame/donor with a bad engine later. Will any CB750 engine fit any frame? any other big issues? thanks

[markreimer]

I spent last winter rebuilding a cb750k4 engine last winter that was rust seized with all new oem+1mm pistons, and rings, MReick valve job, mild porting and it was super fun. So fun  that I wan't to do it again.It runs awesome!  Also to boot I never rode anything bigger than a CB400 until I rode my 74 cb750, and holy crap does it have some pull! So I have been looking for a new winter project looking at hundreds of bikes and specs and have come to the conclusion that our old bikes were not only awesome in their day, but still are wildly better than some new bikes  like a brand new Harley Sportster (a 2001 883 CC  -Sportser has the advantage of 25 years of technology and more cc's and can only manage 50 HP- that is disgraceful). And a 2001 bmw 1200c has only 61hp, Or if you look at an old Beemer airhead you have to go to 1000cc to get to what a cb750 can do. So you all probably knew all this, but I am amazed at how superior the CB750 is. So my next one is going to be another CB750, but since I am so enjoying the extra oomph, I want to go for higher performance on the next one and learn more stuff.

 I have not been able to find a cheap bike with an engine to rebuild, but I see cb750 engines that I just want to buy, rebuild over the winter and then find a titled frame/donor with a bad engine later. Will any CB750 engine fit any frame? any other big issues? thanks

I believe the 69-76 K engines are pretty much interchangeable. You can make a 77/78 work but they have different chain line, carbs, exhaust etc.


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[Powderman]

Your motor only makes 50hp also. You can't compare H-D's and Honda in the same vein, it's tractors and Camaro comparison. Although with a little bit of cash you can do wonderful things with a Harley. Note my avatar.

[calj737]

Your motor only makes 50hp also. You can't compare H-D's and Honda in the same vein, it's tractors and Camaro comparison.

The stock 750 has a higher base HP than 50. Much closer to mid- upper 60s. The 550 had a rated BHP of 50, probably closer to mid 40s in actual fact.

But your point of comparing a 750 to an HD or BMW is afield. Numbers lie greatly. Torque, curb weight, etc all factor greatly into the overall performance of a bike. But, you should have no issue locating a titled frame (try Bill Benton through the forum) to install your motor into.