Topic: CB750 F2 cam shaft in CB 750 K7: Has anyone done this?

[Wobbly]

If so, please share your experience with me (modifications, etc.). Thanks!

[Garage_guy_chris]

this has been discussed a fair bit in combination with the Ebay cruzinimage 836cc kits.  you should be able to find some more info in the thread:


http://forums.sohc4.net/index.php?topic=89779.300

[HondaMan]

It drops right in, uses the same timing. The F2 cam has about 0.4-0.6mm more intake lift than the K7 cam, otherwise the same specs. The powerband will remain the same, but it might just add a little HP boost in the upper RPM range. The F2 exhaust pipe was a 4-1 type that scavenged the cylinder a little more than the 4-4 pipes of the K7-K8 bikes (the 4-4 of the earlier bikes were better scavengers than the K7-8 pipes), so the intake appeared to be boosted to improve the mix ratio on the F2-3 bikes with their slicker valves and smaller stems, to prevent lean-out at high RPM.

[Jerry Rxman Griffin aka MuthaF'er]

Honda manual says the F2 cam has 5 degrees more duration intake and exhaust vs the K7.

It'd be a good swap IMO.

[Don R]

 I had one in my  ported 836 K4 and loved it. Of course I had to try a bigger cam, the jury is still out on the big one. 

[Wobbly]

Thanks guys for all that information. Very useful. Thanks HondaMan for all the details. I greatly appreciate the information here.

I just rebuilt my K7, using tons of new Honda parts I had collected over the past 30 years, replacing things down to the last bolt and washer even if they were still in great condition (she's my baby for 37 years now, and nothing is too good for her). Yet, when I took her to France last weekend, I suddenly found my self covered in oil. The sweating head gaskets are a familiar sight on the 750Fours, but I never have seen anything like this. I did everything by the book, mostly new Honda parts but used the CycleX steel head gasket--which is where the leak seems to be (yes, I did replace the 6 rubber sealings). Because of the new pistons, etc.,. I kept her under 6000 rpms. Anyhow, I also used #41 web cam but can get my hands on a new F2 cam now. And since I have to pull the engine again to take the head off, I figured...That's why I was asking. Again, many thanks.

[Bailgang]

As Hondaman said it drops right in, I put one in my kids K7 and it runs great. The only thing I didn't like was that my kid insisted on using heavy duty kibblewhite valve springs which I thought were ridiculously stiff for the application and would've preferred factory F2 springs instead. Not sure how the F2 cam will work with the K7 valve springs, I guess so long as you don't blow too many shifts they should be fine but hopefully some one else here can give some input on that.

[CB750F2]

From the F3/K8 service manual:-
Intake Opens 5 deg BTDC for the F3 and 0 deg for the K8
Intake Closes 40 deg ABDC for the F3 and 40 deg ABDC for the K8
Exhaust Opens 40 deg BBDC for the F3 and 40 deg BBDC for the K8
Exhaust Closed 5 deg BTDC for the F3 and 0 deg BTDC for the K8.
The figures quoted by the service manual is at a valve lift of 1.0mm
I hope this helps. Pat

[Jerry Rxman Griffin aka MuthaF'er]

The K8 went with F2/F3 stronger springs. After I missed a 1-2 power shift and blew my engine by floating and breaking a valve on the piston I went with stronger springs and a Yoshi cam. All depends on how you ride. I consider it insurance.

If you removed the cam tower studs you could be leaking there if you didn't put some type of sealer on the threads. I also use a little sealer around the puck edges.

CB750F2's numbers confirm my 5 degrees more duration. I was too lazy to look up and type the details. 

[Wobbly]

If you removed the cam tower studs you could be leaking there if you didn't put some type of sealer on the threads. I also use a little sealer around the puck edges

Sure did. the entire valve train is new, to include NOS cam holders. Changed head gaskets before more often than I wanted to, but I never went that far before. Nor have I ever seen such an oily mess. The right side of my leathers is pretty shiny now. I love to watch the oil dripping from my rear tire. It's a slick ride now.

[HondaMan]

If you removed the cam tower studs you could be leaking there if you didn't put some type of sealer on the threads. I also use a little sealer around the puck edges

Sure did. the entire valve train is new, to include NOS cam holders. Changed head gaskets before more often than I wanted to, but I never went that far before. Nor have I ever seen such an oily mess. The right side of my leathers is pretty shiny now. I love to watch the oil dripping from my rear tire. It's a slick ride now.

Umm...did you also install HD studs? With the harder CycleX head gasket, it takes more torque to make them seal. The HD studs will let you tighten to 20 ft-lbs (or even a little more) to help close it up.

With most of today's aftermarket head gaskets, which don't have the sealant coating that Honda always did, I've had to start adding some sealant around the drain holes to make them seal. It also helps to increase the torque a little, or do the multiple-torque routine: I tighten the head down, go home and sleep, then come back and loosen the nuts all 1/2 to 1 turn in reverse order, then re-torque in order again. When hard[er] head gaskets appeared, like the ones in the red-colored "Made in Japan" kits or now, even the Vesrah kits, this leaking business we are seeing became an epidemic.

If you can find my build thread in the Projects section, look through the pictures when I installed the head. You can see where I added the sealant. On the later-style heads with the 8 rubber "dowels", be sure to check the thickness of the (now compressed) head gasket against the OEM gasket: some of the aftermarket ones are thicker than the OEM gasket. The compressed gasket should be just under 1.0mm thick, and they only compress about 0.1 to 0.2mm during installation.

There are also some odd 'new' head dowel seals out there. I first noticed them in the Athena kits: they have a bevel on their inside edges instead of a flat end. The one engine I rebuilt with those (because the customer brought the Athena gasket kit) leaked, and leaked a lot. I pulled it back apart, installed 'regular' rubber dowels from Vesrah, and that fixed it.

[Wobbly]

@HondaMan

Thanks for all that information. I did not install HD studs since nowhere did it say that they are required--I would have never bought that gasket otherwise. I will stick with genuine Honda from now on--thought this would be an improvement. Oh well.
Anyhow, the leak seems to come from above the head gasket, below the cam cover gasket, close #3 spark plug. Leaving that plug out and running the engine, it runs for some time without leaking. Then, suddenly oil spurts out under pressure. The head was installed new a few years ago, has hardly any mileage, and was perfectly okay prior to installing a new valve drive, pistons, etc.
Again, I try to take a picture because, once the engine is pulled, it will be difficult to locate the spot again. It is still difficult to see with the frame in the way. But, I would greatly appreciate it, if you could have a look once a pic is posted, and give me your opinion.
Thanks so much,
Tom (currently very sad and disappointed)

[HondaMan]

@HondaMan

Thanks for all that information. I did not install HD studs since nowhere did it say that they are required--I would have never bought that gasket otherwise. I will stick with genuine Honda from now on--thought this would be an improvement. Oh well.
Anyhow, the leak seems to come from above the head gasket, below the cam cover gasket, close #3 spark plug. Leaving that plug out and running the engine, it runs for some time without leaking. Then, suddenly oil spurts out under pressure. The head was installed new a few years ago, has hardly any mileage, and was perfectly okay prior to installing a new valve drive, pistons, etc.
Again, I try to take a picture because, once the engine is pulled, it will be difficult to locate the spot again. It is still difficult to see with the frame in the way. But, I would greatly appreciate it, if you could have a look once a pic is posted, and give me your opinion.
Thanks so much,
Tom (currently very sad and disappointed)

Ah, the plot thickens...
There are 6 little rubber pucks under the cam bearings (aka "rocker towers) that seal the holes there. They shrink over time and with heat. If they were not replaced with new ones during the last rebuild, or if they were the too-thin ones we have seen occasionally from vendors, or if the cam was changed to a higher-lift, or stronger springs, without first removing and re-sealing them, they like to leak.

There is one in between the 1-2 and 2-3 sparkplugs, and one just above each cylinder's sparkplug.

So...if the head gasket itself is not leaking, you may be in luck (so to speak): you can just (just?) remove the engine, pull off the cam cover and cam, and rocker towers, re-seal those pucks, re-torque the head while you're there (for insurance), then put it all back together. Or, if you measure the little pucks and discover they are the thin ones, you can get the right ones today, and install them instead. They are about $3 each from places like Honda, PartsNmore, or several other vendors who advertise on our SOHC4 site.

I say "in luck" here, as if that means less work, but at least you wouldn't have to pull the head?

[BPellerine]

don't the head and barrels have to be skimmed to use the mls gasket or I thought it was at least recommended?also read some where on here that the rubber dowels are not nec with mls bit I could have it wrong.bill

[Wobbly]

@ HondaMan

The rubber pucks were all replaced (still available from Honda). The original cam was replaced with web cam 41. New cam holders, rockers, shafts, rockers, valves, springs--all (!) there is was replaced with NOS. The new parts are the result of 30 years worth of collecting. Now it was time to use the goodies before dropping dead, and my kids trading the bike for an I-Pod.
The good thing: I just bought that NOS F2 cam on eBay which will go in now. I wouldn't have done this if there was no need to pull the engine again. The head itself was replaced a few years ago-simply because I had a new one sitting. No problems with it before. Not likely for it to develop some crack now, right? Right? I am beginning to panic. Besides, the oil gushes out when it finally appears.
I printed out your pics showing where to put sealant on. Awesome help that should not be buried down deep in your thread. This time, I will follow yours and Jerry Rxman Griffin's advise and get the sealant out. The CycleX gasket will go and I use the Honda gasket again. They worked for 37 years.
I still will take that pic tomorrow. It's already night time here in lovely Germany--and perfect motorcycle weather.
Thanks to all--I greatly appreciate it. 

[BPellerine]

did you not like the cx1?bill

[HondaMan]

@ HondaMan

The rubber pucks were all replaced (still available from Honda). The original cam was replaced with web cam 41. New cam holders, rockers, shafts, rockers, valves, springs--all (!) there is was replaced with NOS. The new parts are the result of 30 years worth of collecting. Now it was time to use the goodies before dropping dead, and my kids trading the bike for an I-Pod.
The good thing: I just bought that NOS F2 cam on eBay which will go in now. I wouldn't have done this if there was no need to pull the engine again. The head itself was replaced a few years ago-simply because I had a new one sitting. No problems with it before. Not likely for it to develop some crack now, right? Right? I am beginning to panic. Besides, the oil gushes out when it finally appears.
I printed out your pics showing where to put sealant on. Awesome help that should not be buried down deep in your thread. This time, I will follow yours and Jerry Rxman Griffin's advise and get the sealant out. The CycleX gasket will go and I use the Honda gasket again. They worked for 37 years.
I still will take that pic tomorrow. It's already night time here in lovely Germany--and perfect motorcycle weather.
Thanks to all--I greatly appreciate it. 

I have now 'witnessed' 3 installations of the CX-1 cam here in the forums that also caused leaking pucks. I think maybe installation of that high-lift cam may require the 6mm bolts that hold down the middle of the rocker towers have extra threads installed into the head, so the torque there can be increased. This, plus the sealant, has stopped the leaks on the CX-1 and Webcam 41a bikes I did here, at least.

I drilled out the existing 6mm aluminum threads in those 4 holes, then threaded new double-length Helicoils into the holes, ending them about 1mm below the surface to ensure a flat top under the rocker towers. This lets you put about 110 in-lbs on those flanged bolts. I also set the cam bearing bolts and nuts to 100 in-lbs, as they help hold the towers down, too.

[Wobbly]

@ HondaMan

I cannot get a clear shot of the leak. It is at the cylinder head behind spark plug #3--where there shouldn't be an opening for a leak, i.e., solid head. It then runs down between the fins--which I can show on the picture. Not likely, that the head suddenly developed a crack, is it? Unheard of as far as I know.

I pull the engines and let you know what I find. Saturday, it's off to Italy with my RR--spring break. I had hoped to take the Honda. Oh well.
If I do not pull the head, I won't have to change its gasket. Do you think then, it be okay with the CycleX gasket, not having the HD studs?
Lastly, in my case, would you still advance a new F2 cam 5 degrees or can I leave it alone?

[Martin Thomassen]

Sorry for hijacking this thread, but I just have a quick question regarding the use of the F2 camshaft in older engines:
Are the F2 valve springs essential a "need to have" or "nice to have" in addition to the F2 camshaft?

[PeWe]

Pulling the engine... so much work....
I used the saw and cut my beloved CB750 since 35 year... I have the head off with engine still in frame. I'll time the cam without removing my PAMCO ignition plate or alternator cover. I have attached photos of my installation in the thread below where other do the frame mod too.

This thanks to Frank (754)
http://forums.sohc4.net/index.php?topic=62832.200

[PeWe]

Sorry for hijacking this thread, but I just have a quick question regarding the use of the F2 camshaft in older engines:
Are the F2 valve springs essential a "need to have" or "nice to have" in addition to the F2 camshaft?

There are other threads with this. Searched on f2 cam + springs
this is one among many...
http://forums.sohc4.net/index.php?topic=17972.msg188308#msg188308
one more
http://forums.sohc4.net/index.php?topic=37520.msg404279#msg404279

[Martin Thomassen]

Sorry for hijacking this thread, but I just have a quick question regarding the use of the F2 camshaft in older engines:
Are the F2 valve springs essential a "need to have" or "nice to have" in addition to the F2 camshaft?

There are other threads with this. Searched on f2 cam + springs
this is one among many...
http://forums.sohc4.net/index.php?topic=17972.msg188308#msg188308
one more
http://forums.sohc4.net/index.php?topic=37520.msg404279#msg404279

Yeah, I already read most of these threads, but I´m still left wondering whether the valve springs needs to be replaced as well. At some point I guess that the stock F2 camshaft won´t make that much of a difference, but then again I don´t know whether the pre ´77 valve springs are already close to their limit when reaching the stock redline (8500 rpm), which then leads to valve float at the increased F2 redline (9500 rpm)?

[Wobbly]

Pulling the engine... so much work....
I used the saw and cut my beloved CB750 since 35 year... I have the head off with engine still in frame. I'll time the cam without removing my PAMCO ignition plate or alternator cover. I have attached photos of my installation in the thread below where other do the frame mod too.

This thanks to Frank (754)
http://forums.sohc4.net/index.php?topic=62832.200

I sooner cut my leg off than my frame. Thanks for the great links, however.

[Wobbly]

don't the head and barrels have to be skimmed to use the mls gasket or I thought it was at least recommended?also read some where on here that the rubber dowels are not nec with mls bit I could have it wrong.bill

Bill, you mean the web cam 41? I couldn't tell any difference in comparison to the stock one aside from the fact that stock isn't available (except for well about 1,000 Euros with tax at CMS in the Netherlands). I prefer stock, but this is robbery. That is why I opted for the web-cam--which sells for twice as much in Germany than in the States, indicating the different price levels in both counties.  Thanks God for military mail, and not having to deal with this unless I am in a hurry. I just bought the F2 cam new on eBay for 199 euros. It's not available new anywhere else on this planet. Anyhow, the bike starts right up with the #41, runs smooth, idle at 1100 rpm. I didn't have the problems that others reported--but my ride was cut short after 200 miles because of the oil leak. I am not after performance gain with the Honda, have my BMW RR for that. It's reliability I want to preserve. I've failed miserably so far.

[BPellerine]

hey you did not fail an oil leak is not the end ,I was just wondering why the cam change but nos is nos and I gather you like that idea you have logged some big miles on your 78 how long did you go with the first set of guides?check out ironworkers thread he used the mls gasket on a stock engine as well.bill