Topic: "Beater" .. 77 CB750F2 .. The engine is now apart

[hashvm]

Sooo beater is back .. I was trying to get this thing running and functioning to check if it runs correctly and if it was in fact worth the time and money

cleaned the carbs (multiple times) until i got it firing finally .. she runs really lean? (runs on full choke only even tho the adjusting screws are 3 turns out and you can actually smell gas as if it was really rich  )

I also changed the carb boots for some cruzinimage ones (they are the only one I could found) .. they seem of a good quality although I'm still having vacuum leak issues

drove it around the parking lot and it a little happy .. put her on the center stand and made sure she shifted through all 5 gears 

So at this point I think my next step is to look into the motor .. My plan is to tackle it carefully and make sure she is reliable

I don't think I'll get any big bore kits or anything crazy on it .. at least for now

maybe a cam?

I know I have a head gasket that I need to change and I was planning on doing a warm compression test to see if I need to change any rings

I read that the valves go bad real fast on these models but is there a way to check it without pulling out the head?

Also anybody knows if  I can do a top end rebuilt with the engine in the frame? or do I have to take it off? (frame kit is coming on pretty soon)

This was my initial thoughts for now .. any ideas or addings are much appreciated

next? maybe this? 

[hashvm]

Removing the head requires pulling the engine or a frame kit. No way around that.

Turning the screws out 3 turns is doing nothing. Swap your jets. You're super lean due to the inexpensive pods. Jet for those, swap them for a higher quality brand, or replace with an airbox.

Cal, I was thinking about getting a kit and install it, then do a top end rebuild .. unfortunately the Gordon frame kit is out of stock 

I'll try to get the airbox installed this weekend and see how she runs ..

Anyone knows of any way I can detect valve failure with the engine intact? (is it supposed to smoke?)

Thanks

[hashvm]

Member "754" (Frank) also sells a non-welded kit you can use.

A leakdown test works very well to help diagnose where your engine is hurt. If it's the valves, you should hear air blowing back into the head or carbs (intake valves) or the header (exhaust valves).

Did you ever get your tank cleaned out? Distilled White Vinegar works very well and is inexpensive. Buy a couple of gallons at the grocery or Home Center. Fill up the tank and let it soak. Rinse, neutralize, then slosh some fresh gas mixed with a bit of oil to prevent any flash rusting. Set aside until your ready to ride.

Cal, I pm'ed Frank to ask about the frame kit. It'd be very nice if I can perform the engine work without taking the whole engine off.

Last night I found some time to work on the bike and got the original airbox back on the bike



Started the bike and ... she started right away and idled very nicely 

It was a night and day difference

here she is

It is still missing the accelerator pump circuit so the bike shuts off if I twisted the throttle fast but as long as I do that gradually she's really happy

and of course .. if the bike is happy, I'll always be happy 

next on the plan is a leak down test before I start taking things apart ..

[hashvm]

So I have been trying to find a place that rent a leakdown tester but with no luck .. anyone knows where I can rent those?

[hashvm]

So last night I managed to do a leakdown test using a harbor fright unit .. the readings were very confusing but at least I reached a conclusion about the valve train.

so on each cylinder I took 3 readings at 3 different pressures and they all turned out the same:
24/30, 54/60, and 86/100 which gives a leakage of 20%, 13.3% and 14% respectively

There was leakage  past ALL valves, I could hear the air going through the carbs to the airbox from the intake and I can sense it coming from the muffler at the back of the bike.

So question 1: now what? which parts are the one usually failing causing the leakage? guides? or the valves themselves?

Also, since the valves were leaking I couldn't really tell the condition of the rings .. I guess that leaves me with one last option which is checking them manually when I take the engine apart.

On a side note, I contacted Frank "754" and got some info regarding the frame kit .. I marked the cuts so I can go ahead and just cut them next time



Hashem

[jamesw]

For an upper triple tree, check these guys out.

They're in Canada which means your stronger US dollar will make the price cheaper.

http://www.ripplerockracers.com/product/honda-cb750f-75-78-cb750k-77-78-and-cb-750c-80-82-billet-top-triple/

[slikwilli420]

If you want something a little more unique, I have quite a few triple tree designs I can do for stock forks or conversions.

[hashvm]

Guides are prone to wear on certain F models, but I was under the impression it was the "exhaust side" not the intake.Carbon build-up on the seats and faces of the valves can easily contribute to leakage. In fact, there's a member in PA (who shall remain nameless out of respect) recently rebuilt his motor only to discover significant leakage. After teardown, he too discovered that the intake valves were badly fouled and they were the cause of compression and pressure leak.

Pulled the valves, cleaned them up, lapped them back in, and he's Jim Dandy. Your actual mileage may vary... But it sounds like pulling the head is in your imminent future.

Cal,
I can easily see carbon being the reason. the bike was running rich for a while and the plugs were night black! 

I'm planning on pulling the head this weekend (hopefully) and we'll see what happens. anything to keep in mind while taking the engine apart?

[hashvm]

For an upper triple tree, check these guys out.

They're in Canada which means your stronger US dollar will make the price cheaper.

http://www.ripplerockracers.com/product/honda-cb750f-75-78-cb750k-77-78-and-cb-750c-80-82-billet-top-triple/

James, thanks for the info.

I'm a mechanical engineering student and was thinking about designing my triple tree in case I do a fork conversion. We'll see if that happens

If you want something a little more unique, I have quite a few triple tree designs I can do for stock forks or conversions.

Willi, thanks I appreciate the offer. I was trying to design my own tree just for practice but I'll let you know if I decide otherwise.

[slikwilli420]

If you want something a little more unique, I have quite a few triple tree designs I can do for stock forks or conversions.

Willi, thanks I appreciate the offer. I was trying to design my own tree just for practice but I'll let you know if I decide otherwise.
[/quote]

You design it, I'll make it. Happy to help if I can.

[hashvm]

Hey fellas, this week has been a productive one

Last weekend I got my frame marked and ready to be cut

Well, I'll let the pictures do the talking ..







I then took my time to carefully taking the engine apart ..
Starting with the valves cover (where I have the first gasket leak) ..



Man this thing was not torqued whatsoever!  the bolts were hand tightened and came out really easily

then I was welcomed by the valve train  (alert: a lot of pictures ahead)









To be continued ..

[hashvm]

Next the cam and rockers came off







I noticed the head had an engraving .. anybody know what this indicates? or is it just a casting mark?



This time I tried to be really organized



Took the exhaust off



Anyone know if this muffler is fixible?



16 nuts and 5 bolts later ..





Carbon, a lot of carbon ..







And here are the pistons

[hashvm]

This brings me to today ..



I took measurements of the cam lobes and its bearings

here are the measurements:

Cylinder 1:
Intake= 36.17mm
Exhaust=35.75mm

Cylinder 2:
Intake= 36.20mm
Exhaust=35.76mm

Cylinder 3:
Intake= 36.18mm
Exhaust=35.90mm

Cylinder 4:
Intake= 36.20mm
Exhaust=35.94mm

This is all within specs which makes me happy 

That's where I'm standing now

any advice or recommendation is recommended

[hashvm]

The muffler could only be salvaged by cutting out and grafting a replacement section. Potential problem is: if theres that much decay, there might be more on either side farther away. That seam is usually where they rot, but rot doesn't stand still. It consumes all possible metal it can get its teeth into.

A very good trick to clean that head (and pistons) is to immerse them in boiling antifreeze to remove all the carbon fouling. Its not destructive, not corrosive, and cheap. Use an outdoor grill and large metal can. The heat won't effect the head at all (as long as you removed the rubber pucks). Keep the pistons and their rings associated. You'll get a whistle clean part back with no elbow grease.

Cal, I'll keep your words in my head

If I went the Cafe route with my bike, I might just swap the muffler for a slip on.

As for carbon cleaning, I can't do the boiling anti-freeze in my current housing, but I'm trying permatex gasket remover and it seems to work for now when I tested it. I might need to find a way to clean tight spots on the head but it should work fine

[hashvm]

I went ahead and got the jugs off so I can get access to the pistons in order to clean them up







I noticed that two of the studs looked like this (I wasn't really planning on changing the studs since I'm keeping the engine with no heavy mods)



Aaaaand within a week she looks like this now

[hashvm]

Also, since I'm gonna be spending a lot of time cleaning, I was thinking about getting some orders going.

First things first is the gasket kit, I was looking at the cycle X top end kit but I heard the MLS ones could still leak if not put with HD studs. Is that right?

O-rings, is there a kit for them or should I order them separately?

Anything else I should consider changing? 

I know it's a lot of questions but bare with me 

Hashem

[hashvm]

The MLS gaskets require perfectly decked surfaces on the jug and head. I'm unaware of the HD stud requirement, maybe so?

Cal, I read somewhere here that since they are made of steel they will experience less compression under the normal studs torque. That's why it's better to have em with HD studs so they can be tightened to higher torque.