Topic: 750F thread?

[Jerry Rxman Griffin aka MuthaF'er]

Wilbur,

The game is on in a few minutes. Quit playing here. Heading to ESPN!

[TwoTired]

The separator drain should have this cap on it.  It has a slit that opens when you pinch it.  The slit will drip out collected water until it is clogged with sludge or debris.  However, if no vacuum is applied to the separator unit, it can't really perform any useful function other than a place to terminate hoses.

I'm curious how an oil tank can operate properly without a vent.  Fill a closed vessel and the internal pressure builds if there is no place for the displaced air to escape.  The opposite is true when trying to empty a full tank when unvented. There are also expansion/contraction from heat/cold issues that need pressure equalization.  A vented cap would allow the tank to function.  But, guess where oil overflow would go.

Cheers,

[Freaky1]

But I didn't think oil came out of these bikes unless we want it to. 

If you look at my build, I already tapped a fitting into the top of the oil cap so I could use either a vented cap (more money) or the one I already have and just run a line out somewhere. The overflow/vent line in the stock tank has a small box around the top of the tube inside the tank. I'd think that was to allow gasses out and maybe a bit of oil but also to restrict oil just draining, say like when your in a turn.

[70CB750]

Gentlemen, I need strategical advice.  I need to decide what to do with the F2 engine I want to use in my build.  The problem is the head now - what a surprise 

I asked one of the vendors who actually sell parts for 78CB750F and here is his answer: (to make it easier to read, I will make my comments inside his reply)

If you install new pre-honed guides they do not need to be re-honed, however you will not be able to just lap in new valves, but must have the seat cut as they will not be perfectly alligned.

I believe he is correct, makes sense to me - opinions?

The stock valves have a stellite weld on the faces and the top of the stems. The valve in the picture has had the stellite fail. There are many reasons that this can happen. The stellite is very thin on the stock valves so if they show wear they cannot be cut and need to be replaced. If a machine shop did not know this and did a butt cut on them the stellite would be too thin and would only last a short while. Worn valve adjusters is nother scenario that will cause this to happen. The adjuster screws have a round dome on them when they are new, but after years of wear they can become damaged and destroy the stellite as well. A common problem is the springs are stacked incorrectly and coil bind. This will not only destroy the top of the valves, but the keeper groves as well.

I believe he is correct, makes sense to me - opinions?


The valve in the picture also has the classic keeper groove wear that is common in the F2. It causes the valves to pop the top off and drop into the motor. There are many differance in the F2 and the other SOHC models. You will probably find the same wear on all of the valves and if you do they will need to be replaced as well. They are in the attatchment and listed below.

The picture I sent him is not the best quality, from what I could see, the groove is in good shape, but I would replace valves anyway - see below.


There are many areas in the valve train of the 77-78F models that can cause engine failure if not upgraded.
The stock valve spring retainers did not hold the collets in place properly and allowed them to dig into the
valve stems. If the collets have printed into your valves, the valves will need to be replaced. We sell our one
piece stainless steel  F2 valves  for $24.95 each.

I agree, based on the valve I seen, I should install all new valves to save some trouble later.


Due to the less aggressive angle of the F2 retainers we always recommend replacing them with our titanium
retainers  that stop the collet problem by holding the collets tightly to the valves. We sell them for $169.95
a set.

I am inclined to believe this is a sales pitch - by all means, nothing wrong with that but for my old fartish style of riding I don't think I need titanium retainers - opinions?


The stock springs had a very high seat pressure that added to the  problems as well. Our springs will give you
 better valve control with less seat pressure. We sell them for $57.95 a set. 

In this point i would trust Honda and skip new springs - opinion?


The stock cam has harsh ramps that is also very hard on the valve train. We recommend replacing it with our
41 grind cam.  We sell them for $194.95.

Sales pitch, I would rather not buy new cam - opinion?

I am trying to decide if I should go with the rebuild or try to find K head in good shape and fit it on?  With the guides, valves, seat grinding it would be definitely cheaper to get and rebuild  K head than follow on with the F head.

What would you consider the minimum package to make this engine reliable for daily commutes and joy rides?  I am closer to 50 than to any other age group and my riding is anything but sporty.  I am not looking for a space shuttle reliability and red-line-all-day performance.  I would like to do the rebuild to last - say - 50 000 miles over the stretch of 20 years  with relativelly low chance of catastrophic engine failure.

Sorry for the long post 

[Jerry Rxman Griffin aka MuthaF'er]

Yes, there are POTENTIAL issues. Is that 'place' going to do the head or just sell parts to you? My inclination if I was keeping the bike would be to do it right completely one time and be done with it. Heads can be expensive. If I was satisfied with my current cam's performance and it was in good shape I doubt I'd replace it. Ditto springs the stronger F2/F3/K8 springs (vs all other 750's) which will help the most at the far end of the redline. Are your retainers loose? Just depends on how much difference you want to/can afford to spend and how you plan on riding and for how long but thats just my opinion. 

Did they mention lash caps for the valve stem tips? 

Oh yeah, if you do the K option you gotta do jugs and pistons too.

[johsch]

Here is a picture of my 750F -76.

[70CB750]

Thank you, Jerry!

The guy I quoted was just a vendor, only selling parts - at least for me, since he is on the other end of the continent.  And no, he did not mention lash caps.

As of now I am inclined to replace all valves, guides, tappets screws - keeping the cam and springs.  Retainers seem to be in good shape, I will check them again with sharp light and magnifying glass to make sure of it.

Tappet screws are available on ebay as regrounds which should be enough with good oil and regular oil change.

[Jerry Rxman Griffin aka MuthaF'er]

You can probably get new tappet screws from Honda, I did. Reground screws?? or rocker arms?

Now that I'm thinking about it I'm not sure if you can use the original retainers with new valves. The new valves may have a different shape cut for the keepers/cotters requiring you to use different ones and the retainers may need to match?? Better check with the head guy on that and lash caps too. MRieck did my head and the Kibblewhite kit came with lash caps to install when I put the cam in. They protect the ends of the stems. 

[Jerry Rxman Griffin aka MuthaF'er]

Here is a picture of my 750F -76.

Looks nice. Can't wait to see what it looks like when it's all together.

[FrankenFrankenstuff]

(Shameless plug) I have a set of FO and F3 ready to go.

[TwoTired]

The F2 has a higher red line than the K models.  And High RPM is quite stressfull to valve train components.  It is also why the cam profile is more "aggressive".

Many of the changes and part recommended are chicken and egg issues, and have much to do with engine longevity.  For this engine, simply not using the extra 1000 RPM red line will almost certainly lead to longer life even with the stock parts.

How much longer?   ??  There are other factors to consider as well.

If the guides are pre hone and are interference fit into the head casting bores.  What keeps the guide I.D. from distorting during press fit?  Further, the act of driving them into place works as a forge to distort he end being hammered.  These install issues can be minimized with heating the head in an oven.

If the stock valves are stellite treated,  are the stainless offerings done that way as well?  Is the stainless as hard as the stellite?

The keeper wear is from both the spring pressure and the reciprocating mass direction change severity (RPM).  Titanium is longer lasting, particularly for High RPM operation.  But, then for high RPM operation you need stiffer springs to get the valve back into its seat.  (Chicken/egg)  If you reduce the valve spring pressure, expect to lose stock red line reliability/ power with the stock cam.  IF you replace the cam with one less aggressive, do you also lose power at high RPM?  Do you lower the red line as well as power?

How important is keeping red line to you?  To my mind the importance of the F2 head it that it offers both power and red line operation.  Will you be happy with changing those characteristics?  If so, why not get a K7-K8 head?  Even a used one will be cheaper than a rebuilt one and give you the same longevity and reliability the CB750 is known for, albeit with less peak power.

Those are my thoughts...
Cheers,

[70CB750]

Thank you, TT!

Redline for me? Lets say that gun it for me means hitting 6-7000 rpms and it does not happen often.

Are you saying the K7-8 head is direct bolt on and no other alterations are needed?

[fr33man]

New tail

hey i have the same tail - do you know if it has a name?

[70CB750]

Donald the Duck? 

[fr33man]

here is my contribution - only photo i have, and ive only had it for a week =)

[fr33man]

Donald the Duck? 

even though it looks kinda gooofy? =)

[70CB750]

 

[Retro Rocket]

Thank you, TT!

Are you saying the K7-8 head is direct bolt on and no other alterations are needed?

NO, you would need new pistons as well as, the F2 pistons have a much higher dome to fit the larger {deeper} combustion chamber of the F2 head.  Stainless valves mentioned are a HIPO part and WON"T have the same problems, my 3 engines have stainless valves. I suggest you send Mike Reick or Big Jay a pm, both are world class engine builders and have dealt with the F2 problems since the bikes inception..

[TwoTired]

Thank you, TT!

Redline for me? Lets say that gun it for me means hitting 6-7000 rpms and it does not happen often.

Are you saying the K7-8 head is direct bolt on and no other alterations are needed?

No.  There is the domed piston thing as mentioned.  So, the CR will be way off.  But, if you are not using the F2's 9500 red line, you'd probably be happier with 836 pistons and the K7-8 head for more torque at throttle twist, as well as long term reliability.  Then you won't need the RPM to get the big power surge.

Pretty sure MRieck doesn't like the F2 head either.  Certainly not for longevity.  I'm thinking you can do the 836 and a lightly used K7-8 head for about the same price as having the F2 head cured of its ills.
I haven't shopped for a while, though.

Cheers,

[70CB750]

Thank you, gents, and my apologies for asking the same question in different threads and taking long time to grasp the concept.

[70CB750]

What do you do for the rubber connectors head - carburator?  For the 1978 F they are not available anymore, correct?

Mine is a special case, the engine came with early carburetors - K2 or K3 - I am thinking about removing spigots and turning them down to accept regular K rubber insulators.

Thoughts?

[brandEn]

Regular K rubbers will fit. I am using them on my F3 head with CR29 carbs made for an early K.

[70CB750]

Thanks, I needed some good news 

[cabrala]

I have followed this thread with envy while riding my mighty 550. It comes with great pleasure to announce my new acquisition...

A 1975 CB750F!!

Bought it in Maine this past weekend. Gentleman rode with Harley guys so the bike is dressed in a Vetter decked out in leather bags and American eagle decals. I have some work to do, but for $700 I got the bike, the original motor (drive chain through the case), Shoei hard bags, rear luggage hard bag, original airbox and a bunch of other goodies that I need to go through.

Bike started up on Sunday after some time not running. It sounded good but is in need of a tune and some maintenance items. All in all I am so very happy and ready to learn.

Alex

[70CB750]

Congratulations!