Topic: 1977 CB750 K7 /// Rebuild 2.0, Project Anna

[mkoski]

So, with the seat now finished, I'm pretty much finished my CB750 project. Here are a couple pics I took yesterday after cleaning it. (All that remains is passenger pegs.)







I'm very happy with the way it looks, came out almost exactly to what I had in mind when I started this project!

Unfortunately, just before I took those pictures I was waxing my bike and tank when I somehow managed to drop my tank, upside-down, onto my concrete garage floor. I could have shed a tear. It scratched deeply through the powder-coat along the top ridge of the tank. I couldn't even bring myself to take a picture of the damage. That's just the way she goes sometimes.

To fix this I either will get the tank re-coated (which is the easiest solution) or get a new tank and swap that on. I read that the F-style tanks fit well? I need a tank that will match up almost perfectly. Is the F tank going to fit like this?

[SOHC4 Cafe Racer Fan]

Very very nice!!  Passenger pegs?!  Probably not necessary given the seat (or it will be a nut buster against the tank). 

Sorry to hear about your gas tank.  I am sure it can be repaired.  The F tanks look awesome on Ks but (as I recall) will require some adjustment of the seat location.

[mkoski]

Thank, I'm pretty stoked on it!

Yeah, it will definitely be a squishy ride and only really tiny girls will fit on there with me but I only ride in the city and I already have mount-points on the bracket and the pegs ordered. I was also thinking, if it was too tight, I could just make a second seat and swap them out!

Well the tank only cost me ~50 bucks to get done and I have a good relationship with that shop (from the thousands me and my friend have put through there...  ) so I could get the whole thing re-done pretty cheaply if I wanted to. I'm looking at this as an opportunity to check out a new tank though. 

I'll have to do some research on the F tanks, I want to see how well it lines up and see if I can find one to test-fit.

[SOHC4 Cafe Racer Fan]

Thank, I'm pretty stoked on it!

Yeah, it will definitely be a squishy ride and only really tiny girls will fit on there with me but I only ride in the city and I already have mount-points on the bracket and the pegs ordered. I was also thinking, if it was too tight, I could just make a second seat and swap them out!

Well the tank only cost me ~50 bucks to get done and I have a good relationship with that shop (from the thousands me and my friend have put through there...  ) so I could get the whole thing re-done pretty cheaply if I wanted to. I'm looking at this as an opportunity to check out a new tank though. 

I'll have to do some research on the F tanks, I want to see how well it lines up and see if I can find one to test-fit.

The lines on the F tank are more rectangular, but I personally prefer them over the more bulbous K7-K8 tanks -- just a personal preference thing (my bike is a K7 with a F tank). 

I think that the easiest solution is to repair your K tank and re-shoot it.  A word of caution as to F tanks: make sure that you pressure test the tank.  The one I used had numerous pin holes that required welding in new panels into the tank -- and the paint looked clean until it was stripped (rust from the inside top that was working itself toward the surface).







As you can see the donor F tank looked clean to the eye

[mkoski]

I agree with that. I really like the more boxy shape of the F tank. I decided to keep it cost-effective though and keep my existing tank. Now that I'm done though I might just have to change my mind.

And yes, a quick re-powder-coat would be the easiest solution so I'll get that done even if I get a new tank.

I'll be sure to check the tank integrity, like you said, as well! Your 9-lives bike is just unbelievable. I love that thing.

[SOHC4 Cafe Racer Fan]

I agree with that. I really like the more boxy shape of the F tank. I decided to keep it cost-effective though and keep my existing tank. Now that I'm done though I might just have to change my mind.

And yes, a quick re-powder-coat would be the easiest solution so I'll get that done even if I get a new tank.

I'll be sure to check the tank integrity, like you said, as well! Your 9-lives bike is just unbelievable. I love that thing.

Thanks.  The tank is presently getting another repair.  Apparently a couple of spots of rust made their way toward the paint and will be fixed by my painter buddy. 

I am pretty certain that the F tank is slightly longer that the K7 tank.  I originally used a stock seat pan, and had to move the hinges to slide the seat rearward to make it all fit.  I am not sure how you mounted your seat, but maybe you can make 2 attachment points for the different tanks.

[SOHC4 Cafe Racer Fan]

Don't forget to "accept" your nomination for the July BOTM thread.

http://forums.sohc4.net/index.php/topic,148308.0.html

[knottedknickers]

I also got a little inventive on my carbs. I know one of the most common complaints/rationals for not using pods/pods not working well is the turbulent airflow coming into the carb throats. In school I took a lot of fluid dynamics courses and remembered a simple device to create laminar flow which has the same principle as using many small tubes to align flow:

Results: significantly improved idle from previous state with simple mod. Still need to balance carbs as I haven't received my vac gauge yet. Will report back after thats completed to really get a picture of performance.

Very interesting 'pod mod'! You mentioned a performance report... How's she go?

[mkoski]

There were some really good results from that little mod, I had to pull the little straw bundles out though as a bit of gas was getting on them which was loosening the electrical tape. I just need to attached them together in a stronger fashion before I can give a good result of the mod. That, however, is on hold now due to a large issue that occurred two days ago...

Sunday night I was out for a ride and heading home when I lost oil pressure around one mile away from my house. I was on a major road with a high speed limit when I noticed my engine began to lack power and run a little funny. This lack of power was accompanied by a fairly loud ticking in the top end of my engine almost immediately after the power loss was noticeable. I made an exit and noticed that at idle I had to give some throttle to keep the engine running. This felt like I was fighting piston/sleeve friction.  I brought it into my garage. I tried using the electric starter to turn the engine over and it would not turn. Unbeknownst to me at the time, my oil filter on the front had ruptured and caused me to lose a lot of oil. I left my bike to cool for the night after looking in the oil tank, confirming that there was no oil.

Yesterday morning (Monday) I went to my bike and hit the electric start. The engine turned over no problems and seemed to sound okay. I did not start it as it had no oil. After work I picked up a bunch of oil and went home and changed the oil twice and also the oil filter. I didn't find any obvious signs of metal in the oil. I fired the bike up after circulating oil with the starter for a bit and it started fine and seemed to sound okay, besides slightly-louder-than-before valve-train sounds. I revved it up a bit and it sounded fine so I took it for a ride. While riding I could feel the same symptoms of when I was riding home Sunday night. A loud ticking sound was apparent when the engine was under load. The bike would rev up more slowly and produce very little power.

So my question to you guys is this: from the lack of power and ticking in the valves when under load I am sure I need to do a top-end rebuild/inspection. What else should I look for and what specifically do you guys think is causing this issue? My best guess thus far is that a valve or rocker is stuck/damaged and this is causing a cylinder to not fire, causing the lack of power. Does that sound right?

Tonight I am going to remove tappets to check valve clearances and make sure nothing is loose then test compression across all four cylinders. This should give me some idea of what might be wrong.

[SOHC4 Cafe Racer Fan]

This is where a frame kit can come in very handy.  Sorry to hear about your oil issue.  I am not sure how long you were running the motor and whether the top end suffered any significant oil starvation issues.  Others can better advise you as to whether a visual inspection from the tappet covers is sufficient or whether you need to look at the valve train with the cover off.  IF you do end up having to pull the motor, install a frame kit.

[SOHC4 Cafe Racer Fan]

Cal,

Any opinion on whether he can see enough from the tappet holes, or whether he needs to pull the valve cover?

[SOHC4 Cafe Racer Fan]

I've been having waking dreams/nightmares of seeing your tank fall and bounce, and hearing the sound of you yelling "NOOOOOOO" in slow motion and the clang of the tank.  Luckily it's completely repairable!!

[knottedknickers]

There were some really good results from that little mod, I had to pull the little straw bundles out though as a bit of gas was getting on them which was loosening the electrical tape. I just need to attached them together in a stronger fashion before I can give a good result of the mod.

My mind is going on this one! How long do the straws need to be to create laminar flow? Yours look about 3 cm long--is that about right? Just looking at the 'end-on' picture of the straws packed in the filter rubbers makes me wonder about the spaces between the straws (i.e., not the straw hole, but the other 'holes')... I'm assuming one wouldn't want these closed in as it would restrict airflow, right (which rules out gluing them together with Gorilla glue or something like that; maybe a small dab of CA glue between each straw would work)? And because the gaps are straight in relation to the straw holes, they're contributing to laminar flow, right (i.e., the air passages don't all have to be round, just parallel)? I'm just racking my brain thinking where I've seen some suitable 'honeycomb' material... Probably in my dad's shop (he's got a bit of everything... ) It'd be nice to find something 'prefab'.

Sunday night I was out for a ride and heading home when I lost oil pressure around one mile away from my house.

BUMmer! You heard about the guy who heard most accidents happen a mile from home? He moved... Hope you get to the bottom of it without too much trouble.

[SOHC4 Cafe Racer Fan]

Cal,

Any opinion on whether he can see enough from the tappet holes, or whether he needs to pull the valve cover?

Unlikely. I'd think the cover has to come off for a proper inspection. Given that he just finished a lengthy and comprehensive rebuild, he'd want to err on the side of caution and verify the top end, and diagnose the original cause of the oil pressure lost (I saw the notation about an oil filter blowout, but I don't know what that means)

Without knowing whether the oil filter seal blew out causing the problem or was the result of a pressure build up, I agree that it makes most sense to pull off the valve cover for a look see.

[Restoration Fan]

Personally, I'm not sure I'd even be comfortable after only pulling the valve covers.  I would most likely go ahead and at least remove the head so that I could see down into the cylinders and see if there is any obvious damage. 

Then rotate the crank and watch the pistons move through a full series of travel just to confirm that a piston ring isn't broken, seizing or something.

The cost of a new head gasket and a few hours of time putting it back together would greatly be paid for by having seen down in there.  Just my opinion but it's what I would do.

[SOHC4 Cafe Racer Fan]

Ron - there's no "right or wrong way" with these situations. However, I'd submit that, oil for the cylinders is from beneath the piston, and a loss of oil pressure isn't usually associated with a broken ring. If his motor cranks and runs, but then looses power, suspicions would be head/valve train (damage to the cam, rocker, valve, etc). Pull the valve cover first anyway, it will usually tell you how deep you have to go to repair the damage. But the head is probably coming off shortly anyway.

Me, I'd investigate as I go, turning, measuring, observing. It's a good sign that his repeated oil changes didn't contain any measurable metal or alloys! Quite possibly, he did such a good job building it, and quickly enough to stop the motor, that he may not have done any real damage. Or at least, minimized the damage.

And the oil pump and returns fortunately are outside the engine, so fingers crossed, he won't be pulling cylinders or splitting cases!

This sounds like a prudent way to go about it -- along with adding in a frame kit.  I never thought I would ever pull the motor after its initial rebuild.  Two more times (for top end issues) taught me a good lesson to install the bloody frame kit!

[Restoration Fan]

Ron - there's no "right or wrong way" with these situations. However, I'd submit that, oil for the cylinders is from beneath the piston, and a loss of oil pressure isn't usually associated with a broken ring. If his motor cranks and runs, but then looses power, suspicions would be head/valve train (damage to the cam, rocker, valve, etc). Pull the valve cover first anyway, it will usually tell you how deep you have to go to repair the damage. But the head is probably coming off shortly anyway.

Me, I'd investigate as I go, turning, measuring, observing. It's a good sign that his repeated oil changes didn't contain any measurable metal or alloys! Quite possibly, he did such a good job building it, and quickly enough to stop the motor, that he may not have done any real damage. Or at least, minimized the damage.

And the oil pump and returns fortunately are outside the engine, so fingers crossed, he won't be pulling cylinders or splitting cases!

Good advice.  I wasn't saying that he necessarily had to but I was just saying that if I'm pulling the engine from the frame, I would personally go the extra step and check the cylinders.  You're right that it sounds like that might be overkill but I have gotten lazy in my older age and I'm averse to being stranded.  Just my overly paranoid nature, I guess.

[Restoration Fan]

Maybe it's where you live and ride, Ron? Time to upgrade your neighborhood. D Too many pool parties going on perhaps?

Probably so, Cal.  Heck, I could only afford an E class for my wife.  Couldn't step up and go big time for the S-class like some people I know of! 

[mkoski]

I've been having waking dreams/nightmares of seeing your tank fall and bounce, and hearing the sound of you yelling "NOOOOOOO" in slow motion and the clang of the tank.  Luckily it's completely repairable!!

Me too, cold sweats.  I just picked it up and went and grabbed a beer. It's funny how little I care about that now with my engine all frigged now. 

[SOHC4 Cafe Racer Fan]

I've been having waking dreams/nightmares of seeing your tank fall and bounce, and hearing the sound of you yelling "NOOOOOOO" in slow motion and the clang of the tank.  Luckily it's completely repairable!!

Me too, cold sweats.  I just picked it up and went and grabbed a beer. It's funny how little I care about that now with my engine all frigged now. 

Don't despair about the engine.  Pull it out and give yourself some peace of mind, and while you're at it install the frame kit.  The down time should be about the same as it will take to repair the tank and re-coat it.  Still plenty of time to enjoy it this Summer.

[mkoski]

And in response for all the advice about my top-end:

I agree with you guys. The idea of pulling my engine makes me very sad but its a big opportunity to do some work on the engine. I ran the engine last night and she's firing on all four cylinders (they are all equally hot and idle seems to be okay) so valve-train and cam are the most obvious culprits for the sounds (very apparently coming from under the cover). My plan is to pull the engine and take a look at the cam/valves. If its something apparent right off the bat I should be able to replace it and get her back on the road... If not, I will settle into the bigger work of doing the entire engine and buy a new (old) bike to ride for the remainder of the summer. I want to do things right but I also want to ride.

That's the plan for now. This weekend I'll pull er and see whats up. Lots of pictures will be coming up!

[SOHC4 Cafe Racer Fan]

What VERY little consolation there is, your bike is still up for BOTM. 

When my CB750 motor was initially rebuilt by a pro, I was told not to bother with a frame kit.  It leaked like a sieve when it was first fired.  The motor was pulled 2 more times to correct leaks.  Even though it was "rebuilt" all of the original OLD seals were used and a few o-rings were missing, too.  My 750 now has a frame kit!  I learned the hard way.  I began to think that my bike was cursed.  She now runs great -- and yours will too.

The good thing is that you've taken down this motor and your problems are almost certainly limited to the valve train.  This should not take all summer, but maybe a week to three, provided you have the help to pull and re-install the motor. 

[mkoski]

What VERY little consolation there is, your bike is still up for BOTM. 

When my CB750 motor was initially rebuilt by a pro, I was told not to bother with a frame kit.  It leaked like a sieve when it was first fired.  The motor was pulled 2 more times to correct leaks.  Even though it was "rebuilt" all of the original OLD seals were used and a few o-rings were missing, too.  My 750 now has a frame kit!  I learned the hard way.  I began to think that my bike was cursed.  She now runs great -- and yours will too.

The good thing is that you've taken down this motor and your problems are almost certainly limited to the valve train.  This should not take all summer, but maybe a week to three, provided you have the help to pull and re-install the motor.

Hahaha, its a pretty big consolation. I'm very stoked that I built exactly what I like and everyone thinks its pretty cool. =)

Thanks for the encouragement. You are correct, I should have a diagnosis on the problems this weekend, parts on order Monday and then problem solved and back in within a week or two.

[Davez134]

When you do figure it out and fix it, (which you will) don't use words like "complete, done, finished, fixed" I have found them to be bad luck If you must, then modify with "hopefully, or for now."  seems to have worked for me!

[SOHC4 Cafe Racer Fan]

When you do figure it out and fix it, (which you will) don't use words like "complete, done, finished, fixed" I have found them to be bad luck If you must, then modify with "hopefully, or for now."  seems to have worked for me!

Too true . . . .