Topic: CB Rebuild

[itzbrad_CB350f]

Hello,
I am brand new to the forum. I just finished a rebuild on a nice CB350F. Head and cylinders came off. New rings. everything cleaned. Cylinders honed. Carbs rebuilt. So its back together now and not even a hint of starting. I admit i messed it up somewhere. It appears to be getting fire and fuel. Any ideas?

[OldSchool_IsCool]

Welcome to the forum Brad!

All you need for these bad boys to start is:
1- compression
2- proper air/fuel mix in cylinder
3- hot spark delivered at the right time

Lets check/eliminate the easy stuff first. 

Well-timed hot spark:
- Is your battery fully changed?
-- a weak battery will not fully saturate you coils, especially if you are using the electric starter. 
-- put your battery on a battery tender if you have doubts.

- Are you getting spark?
-- with your fully changed battery, pull out the plugs (yes, all 4)
-- hold the plugs to the cylinder block and look for a fat, blue spark on each plug

- Is it timed properly?
-- The Honda CB-four uses a wasted spark ignition.  Specifically, 1&4 fire together and 2&3 fire together.  Under normal configuration, only one of the cylinder pairs will have fuel/air compressed at the time of the spark.  The other cylinder would be finishing it'sexhaust strok and is only now drawing in fresh fuel.
-- Assuming you have points, 1&4 fire off the BLUE wire and 3&4 off the yellow.  With your gas tank off, is the BLUE wire connected to the coil that feeds 1&4 plugs?
-- What is your point gap set to ( the gap when the points are OPEN to their max, you can eyeball this as you turn the crank clockwise by hand)
-- With the gap set right, connect a lamp or volt meter across your BLUE points (left side), does the lamp turn on or meter go to 12v when the timing mark is pointing to F of 1.4?

That's plenty to chew on for a while.  Report your findings back here.

[baronsmear]

hey,
i'm just about to the point of putting it back together as you have...but i'm freaking out about putting the new pistons in.  how in the world did you lower the cylinders onto the pistons without messing up the rings and/or the gasket?
thanks for any help you can offer,
brian

[ev0lve]

You can use just use your fingers to compress the rings if you've got a second person there to move the head down evenly. It will give you "the fear" though - or at least it did for me Otherwise there's a tool for that. You can tack the gasket down with some gasket glue - Gaskacinch worked well for me. One way or another - sloooooooowly.

[CBGBs]

Cam position??

[tomkimberly]

To hold the pistons in place, you can purchase two of these or make your own.


http://www.hondaminitrail.com/gifs/T12.jpg


Tom

[baronsmear]

not the cam piston...sorry, i should've been more specific.  -or maybe the cam piston...i dunno what the proper name is for the pistons.  but they're the main pistons, if that is any clearer...sorry.

that tool to hold the pistons in place...how does that thing work?  i can't make heads nor tails of that thing.

am i just better off if i do this like i would a car?  -take the oil pan off, take the rods off the crankshaft, attach the cylinders to the crankcase, drop the pistons and rods into the cylinders and then attach the rods to the crankshaft?  neither manual i own talks about doing this, which is where my hesitation comes into play.

thanks, guys.

brian

[tomkimberly]

not the cam piston...sorry, i should've been more specific.  -or maybe the cam piston...i dunno what the proper name is for the pistons.  but they're the main pistons, if that is any clearer...sorry.

that tool to hold the pistons in place...how does that thing work?  i can't make heads nor tails of that thing.

am i just better off if i do this like i would a car?  -take the oil pan off, take the rods off the crankshaft, attach the cylinders to the crankcase, drop the pistons and rods into the cylinders and then attach the rods to the crankshaft?  neither manual i own talks about doing this, which is where my hesitation comes into play.

thanks, guys.

brian

They slip over the connecting rods and prevent the pistons from dropping down into the engine cases.

You don't need to use them if you have someone helping, but if you are doing the job by yourself, they are most helpful.


Tom

[OldSchool_IsCool]

Like Tom said, the tool slips around the connecting rod under the piston.  You will need 2 of these pistons holders (or your home made version, I used square tubing) 

It's job is to basically hold the pistons still and level as the cylinder block is lowered over them.  Start with pistons 2&3.  Once you have those rings in their cylinders, move 1&4.  Two people helps, but it can be done solo with the right amount of finesse and curse words.

[itzbrad_CB350f]

Thanks for the advice. All good stuff. I am sure it is a timing issue so we'll focus on that.

As for the cylinder slipping over the rings, I had an extra set of hands and we did it the old fashioned way. Only broke one set of rings too. Someday i will buy a ring tool.

[itzbrad_CB350f]

Got it started. Timing was off 180 degrees.

[itzbrad_CB350f]

Here are before during and after photos. $600 for a decent 350f,  $1000 or more (i stopped counting) worth of new parts, beadblasting, and powdercoating and you get a decent looking cafe racer.

http://s569.photobucket.com/albums/ss136/itzbrad_cb350f/?albumview=slideshow