Topic: 1979 CB750 Engine Work

[bayerja]

I have a 1979 Cb750 F with a locked up engine.  I pulled the engine and tore down the top end.  Cylinder 1 has some rough spots in the sleeve and the piston rings were stuck pretty good.  I've got one ring that still won't come out and possibly one other piston that is damaged from taking the rings out.  I use a bore to ream out the cylinders.  Number 1 still has a few soft ridges in it. 

Im wondering if i buy a set of honda OEM used cylinders off ebay and shove those in there, i stand a chance of getting it running.  I know there are some specifics on the sizing of the rings to the cylinder sleeves but if I've simply run a bore through it at this point.

I'm trying to aviod pluging much more money into this bike since it started with as a doner bike for my cafe project.  I came up with a great plan to get a title for the frame, and now that I have it I'm determined to get it running.

2nd option:  Does anyone have a DOHC engine that turns over?

3rd option: Does anyone need a DOHC frame with a title?  I have all the other parts of the bike.     

[lucky]

I have a 1979 Cb750 F with a locked up engine.  I pulled the engine and tore down the top end.  Cylinder 1 has some rough spots in the sleeve and the piston rings were stuck pretty good.  I've got one ring that still won't come out and possibly one other piston that is damaged from taking the rings out.  I use a bore to ream out the cylinders.  Number 1 still has a few soft ridges in it. 

Im wondering if i buy a set of honda OEM used cylinders off ebay and shove those in there, i stand a chance of getting it running.  I know there are some specifics on the sizing of the rings to the cylinder sleeves but if I've simply run a bore through it at this point.

I'm trying to aviod pluging much more money into this bike since it started with as a doner bike for my cafe project.  I came up with a great plan to get a title for the frame, and now that I have it I'm determined to get it running.

2nd option:  Does anyone have a DOHC engine that turns over?

3rd option: Does anyone need a DOHC frame with a title?  I have all the other parts of the bike.   

I have a 1978 CB750 frame for sale now WITH a title and it is powder coated gold.

[bollingball]

You have a DOHC. Are the mounting points the same as a SOHC? I'm thinking other things may not line up either. But I don't know much about the 79 DOHC. You may want to post in the (OTHER BIKES) You would get more answers there.

Ken

[onepieceatatime]

Lucky, He has a titled frame, he is not looking for a frame.

  I came up with a great plan to get a title for the frame, and now that I have it I'm determined to get it running.

Bayerja,
How did you get the title?

[bayerja]

I got the title from a guy off ebay.  He doesn't do titles anymore unfortunatly.  i just asked him to get me one for a bronco this morning and he said he wasn't in the business any longer. 

I know I have a DOHC.  This is pretty generic question on the piston rings though.  I thought someone here might be able to answer.

[onepieceatatime]

I got the title from a guy off ebay.  He doesn't do titles anymore unfortunatly.  i just asked him to get me one for a bronco this morning and he said he wasn't in the business any longer. 

I know I have a DOHC.  This is pretty generic question on the piston rings though.  I thought someone here might be able to answer.

OK, thanks for the info. I have a DOHC 900F engine that came with my '81 750F, but the PO told me the bottom end bearings were bad. It is just taking up space in the garage. I would offer a trade on the locked up 750 engine, but that is kind of a long ways to go. Check Greggo though, He just got a bunch of DOHC parts when he bought a load of SOHC parts... I am buying some of them from him, but I know he has more available including a couple 750 engines.

http://forums.sohc4.net/index.php?topic=111413.0

[Xnavylfr]

As far as your question about DOHC and SOHC frames!! NO a DOHC engine won't JUST fit in there, the DOHC engine is about 3 inches wider. Of course you could modify the frame but by the time you're finshed you could have built a complete new frame.
 If you buy new sleeves/jugs off E-bay you won't be able to JUST install them with your pistons and expect all things to be perfect. The cyls could have been oversized and the PO didn't know it so they get advertised as STOCK jugs. Better for you to find another engine that spins and start from there!!!


Xnavylfr(CHUCK)
I have a DOHC engine but shipping would cost a BUNCH for something that weighs 200lbs.

[thrownchain]

I take it from you're description, that your honed the cylinders? If there are still pits in the cylinder wall, then you're probably needing to bore the cylinders. You also state that the pistons may be damaged? So you're also looking at new pistons.  Instead of trying to "cheap" it, got new oversize pistons and bore it to match. Costs$, but farther ahead in the end.