Topic: CB750 F3 top end questions

[Davidov]

Starting teardown on my 78 CB750 F engine. I found the 5mm bolts on the rocker shaft for Cylinders 1 and 2 were loose.

They seemed to have been that way for some time, the bolt hole on the cam holder/tower is wallered (technical term?) out.

Is this from a previous lack of proper work, without torquing properly. Anyone seen this before?

[flybox1]

might not need them anyway if you're going by suggestions in HondaMans book 

[70CB750]

Exactly, you are better off without them.  It allows the rocker shafts move more which leads to better lubrication and longer life of those shafts.

[Davidov]

Shoot, the more I see HondaMan's book referenced, the more I see the need for it.

[flybox1]

Shoot, the more I see HondaMan's book referenced, the more I see the need for it.

Yup! 
Dont get me wrong... you can do a rebuild with the shop manual, and help from the forum, but Mark put this together with the layperson in mind, and he did a fabulous job. 
The book is invaluable. 

http://www.lulu.com/us/en/shop/mark-paris/my-cb750-book-hardcover-edition/hardcover/product-16107855.html

[ekpent]

I think the 'wallered' shape you describe is normal.

[70CB750]

I just noticed it is F3 you are taking apart.  How many miles and was there a reason for the rebuild?  Also curious what shape are your valves and guides in.

What is the plan?  Rebuild with new parts or you don't know yet?

[flybox1]

I just noticed it is F3 you are taking apart.  How many miles and was there a reason for the rebuild?  Also curious what shape are your valves and guides in.

What is the plan?  Rebuild with new parts or you don't know yet?

+1
If this is an area you plan to focus on, OEM Honda valve guide seals are highly recommended for the F's.
 

[Davidov]

I searched around this forum, and found a little info on removing these rocker bolts.
If I discard and run without the 5mm bolts, do I need the early style rocker shafts?

I just noticed it is F3 you are taking apart.  How many miles and was there a reason for the rebuild?  Also curious what shape are your valves and guides in.

What is the plan?  Rebuild with new parts or you don't know yet?

Reason for the rebuild; there are a few common oil leaks (head sealing pucks, head gasket) and I found compression was a little on the low side (around 100-110). A little over 20,000 miles.

Haven't got down to inspecting the valves yet.

It looks like someone has been in the engine before. The P.O. "claimed" the guy before him did "valve work", but admitted he had no way to prove it.
There were some scratch marks on the frame, by the exhaust studs. Someone used sealant on the valve cover gasket, and the box of parts that came with the bike had a new cylinder base gasket. 

I'm hoping to get lucky and find updated/improved valve guides.
 

+1
If this is an area you plan to focus on, OEM Honda valve guide seals are highly recommended for the F's.
 

I am planning on using Cycle X's super top end set.

[MCRider]

No you don't need the early style shafts. Mark was threatening to make some that incorporated all the god points of each iteration. Don't know if he ever did. Best to have is the wasp waist style with nothing else added.

[70CB750]

I searched around this forum, and found a little info on removing these rocker bolts.
If I discard and run without the 5mm bolts, do I need the early style rocker shafts?

No, these will do just fine.  That's what I did on my K3F - and I am not that smart or experienced.  It is based on HM book studies of course.

Honda was trying to quiet down the valve ticking, that's why the M5 bolts are there.

[flybox1]

+1
If this is an area you plan to focus on, OEM Honda valve guide seals are highly recommended for the F's.
 

I am planning on using Cycle X's super top end set.

Yes, you can use any aftermarket seal you want.       

[Davidov]

+1
If this is an area you plan to focus on, OEM Honda valve guide seals are highly recommended for the F's.
 

I am planning on using Cycle X's super top end set.

Yes, you can use any aftermarket seal you want.       

Sure, OEM Honda is the way to go. Are the aftermarket seals inferior? The OEM nok seals work better for used valves? Information goes a lot further than an eye rolling smiley haha

[70CB750]

I did use the cyclex head set with MLS.  Quite happy with the overall experience, but the engine was not started yet.

The MLS helped a lot when clocking the camshaft, I took the head off and installed many times and you could not tell by the gasket.

[flybox1]

OEM stem seals are better quality and will seal better on the F guides.  Just a suggestion to keep you from going back in to replace aftermarket seals that cause troubles....
I have a baggie full of aftermarket seals you can have    I'll even pay for shipping 

[Nic]

Before you just take out the 5mm bolts you need to check the shaft for wear. It's advised to use new shafts if you are going to let them rotate. Easy way to check is to adjust the lash on each valve, put a feeler gauge in there n make it whatever you want, then with a screwdriver in the end of the shaft rotate the shaft to see if the feeler gets tighter or looser.
 So now you can see if you just take out the 5mm bolts with worn shafts what will happen as the shaft rotates.

[70CB750]

Since the F3 needs new guides in under 30000 miles my shafts checked ok.

[70CB750]

One thing I found later during the rebuild was that I need new tappet adjustment screws, got them from Dynomen. The old set was all distorted from eating up my valve ends.

[Davidov]

Before you just take out the 5mm bolts you need to check the shaft for wear. It's advised to use new shafts if you are going to let them rotate. Easy way to check is to adjust the lash on each valve, put a feeler gauge in there n make it whatever you want, then with a screwdriver in the end of the shaft rotate the shaft to see if the feeler gets tighter or looser.
 So now you can see if you just take out the 5mm bolts with worn shafts what will happen as the shaft rotates.

Nice tip, thanks!

[Davidov]

I got it disassembled, these orange o-rings in the center on each side of the cam chain hole look like they got smashed on reassembly.

I'm a little confused about the necessary o-rings and stud packing gaskets. I know there should be 4 little o-rings on the cylinder head, 2 around the oil jets.

Does anyone have a better guide to installing these in the proper locations?
Also, I have rust on the foward studs that are open to atmosphere. I've heard of using heat shrink tube over these. Is that the best method?

I know, tons of questions, but I'm trying to make this a "right the first time" build.

[flybox1]

get the HondaMan book and read this!!!
brandEn's leak free top end rebuild thread...
http://forums.sohc4.net/index.php?topic=107040.0

[MRieck]

I would highly recommend using the new Kibblewhite iron guides CycleX just released....you will get much longer life out of them.