Author Topic: CB750F newb top end questions - with good pics  (Read 1322 times)

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Offline wohali

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CB750F newb top end questions - with good pics
« on: December 03, 2010, 08:38:29 PM »
Hi there - long time lurker, (nearly) first time poster.

Last weekend I started the rebuild on my 77/78 CB750F with the engine pull. Tonight I got through the top end disassembly. Image galleries are here and here, respectively.

Two questions. First, when I got the top cover off, the inside is showing these odd cracks that don't go all the way through, and one scratch I can't figure out how it got there (hard to see due to what I think is possibly factory permanent marker!) Are these anything to worry about? Are they common? The cover feels solid enough, but I can get my fingernail into the crack. I have higher res versions of these photos if it'd help.

The other may be a bit more serious. After removing the 3-4 rocker shafts, I noted some small indentations inside the raceway in the cam / rocker tower (only one shown here). Should I be trying to sand these out? I am nervous they may have been damage caused by the removal process.

Big shout out to Hondaman - your signed 1st ed. book is in the photos, and starting to get covered in oil :) Much more readable than the Clymer or Haynes or even the Honda manuals! So far I have one suggestion for future printings. You say "if the cam is holding a valve up, you will need to loosen the nut and adjuster screw." I recommend saying "just go ahead and loosen all the nuts and adjuster screws" or perhaps "go ahead and loosen all the nuts and adjuster screws for any rocker that doesn't freely move with your index finger."

Thanks for reading my post!

Offline brandEn

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Re: CB750F newb top end questions - with good pics
« Reply #1 on: December 03, 2010, 09:21:31 PM »
I don't think the cam cover is anything to worry about. The cracks are normal. The scratch or gouge looks like your bike had some top end trouble in its previous life. I don't think there is any reason to replace it if those are the only defects. The cam rocker journal (looks like damage from removal), well if it were mine I would replace it. I am rebuilding a 78F now so if you have any questions I will do my best to help! Check out my build thread.

http://forums.sohc4.net/index.php?topic=76757.0
« Last Edit: December 03, 2010, 09:31:30 PM by BWJ »

Offline wohali

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Re: CB750F newb top end questions - with good pics
« Reply #2 on: December 03, 2010, 09:56:03 PM »
Thanks BWJ. I don't mind replacement IF it's really necessary AND it's not impossible to find the part. I don't have a lot of time to troll eBay for these things and really, REALLY don't have the time to do a second engine buy and teardown just to get a hold of one, but if you & others think it's going to be essential to prevent long term damage...

Offline brandEn

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Re: CB750F newb top end questions - with good pics
« Reply #3 on: December 03, 2010, 09:59:52 PM »
You bet. I will be the first to admit I am no expert with these engines so don't take my word as gospel...lol. Keep your eye on the parts for sale section as there are always good deals and parts to be had. You could also post a thread in the parts needed section, I have had GREAT success doing this.


Offline wohali

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Re: CB750F newb top end questions - with good pics
« Reply #5 on: December 03, 2010, 10:07:43 PM »
Wow talk about a fast response! :) Will the '76 CB750E-25***** match onto my CB750E-31***** OK? I guess I'd have to take the ENTIRE tower/rocker set and put them on as one unit, instead of keeping what I have and just using the tower, since it won't be wear matched...right?

Oh! I forgot to take cam pics. There's some rough bits on the EDGES between the horizontal surface that does the business and the vertical surface, but I suspect this is OK (and probably should be lightly filed/emeried down? Will get to the cam pics tomorrow, and probably finish the inspection on it too...

Online bryanj

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Re: CB750F newb top end questions - with good pics
« Reply #6 on: December 03, 2010, 10:27:07 PM »
Ignore the lot, casting marks in the cover and the shaft that goes in the cam tower where the marks are doesn't turn so it don't matter
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline wohali

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Re: CB750F newb top end questions - with good pics
« Reply #7 on: December 03, 2010, 10:29:09 PM »
Thanks bryanj, you put my mind at ease. :) Cam pics tomorrow!

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Re: CB750F newb top end questions - with good pics
« Reply #8 on: December 03, 2010, 10:33:55 PM »
If its really a 77/78 F you need to check the valve guides for wear, especially the exhausts as they were/are a known bad part
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline brandEn

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Re: CB750F newb top end questions - with good pics
« Reply #9 on: December 03, 2010, 11:28:28 PM »
Ignore the lot, casting marks in the cover and the shaft that goes in the cam tower where the marks are doesn't turn so it don't matter

That makes sense.

wohali-Sorry if my previous post about your cam tower got you worried.

Offline wohali

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Re: CB750F newb top end questions - with good pics
« Reply #10 on: December 04, 2010, 12:09:19 PM »
If its really a 77/78 F you need to check the valve guides for wear, especially the exhausts as they were/are a known bad part

Yup - well aware of this from the awesome posts on this forum! I'm not to the inspection yet, just disassembly and documentation. As an engineer I am a bit of a stickler for process and procedure ;)

BWJ: No worries :) I had forgotten too, the 77 era engine has the extra 5mm bolts that definitely prevent the shafts from rotation, so as long as it's not a HUGE gouge I don't see an issue now.