CB400T Shitbox Build - Daily Driver

[8ball]

Sounds more like a rod knock......possibly. Hard to tell over computer audio. Here is a quick and dirty way to tell. Remove one spark plug (leave one in for compression resistance) and manually rotate the engine while looking down one plug hole. Stop rotating as the piston is on its downward stroke. Take a screwdriver and push down on the piston lightly. If the piston moves before trying to rotate the crank, you have a bad rod bearing. There should be no perceivable slop between the piston, rod and crank.

Repeat on the other cylinder

[steveo]

It might be worth balancing/cleaning your carbs before going any further.

[jakejensen]

Sounds more like a rod knock......possibly. Hard to tell over computer audio. Here is a quick and dirty way to tell. Remove one spark plug (leave one in for compression resistance) and manually rotate the engine while looking down one plug hole. Stop rotating as the piston is on its downward stroke. Take a screwdriver and push down on the piston lightly. If the piston moves before trying to rotate the crank, you have a bad rod bearing. There should be no perceivable slop between the piston, rod and crank.

Repeat on the other cylinder

Thanks for the tip 8ball! I'll see what happens.

Just checked out your Suzuki build thread, awesome stuff!

[jakejensen]

It might be worth balancing/cleaning your carbs before going any further.

Good call, others have said the same. I started out by (like an idiot) tearing into the front forks and brakes. I wanted to replace the seals in the forks (they had some weird looking corrosion going on, turned out to be water from the cracked dust seal), and because I'm a novice I figured I would just rip out the whole triple tree and headlight. Anyways, It needed new brake pads and the calipers were a little scratched up. Long story short Ive cleaned the all the brake components and the pistons all look to be in real good condition. The rotors are in good shape, but I'm still kicking around the idea of new drilled and slotted ones for better braking in the wet of Berlin. I cannot for the life of me find any that bolt up to this bike. I checked EBC and SPS and they don't have any, unless I fucked up the search. I'm going to paint and seal them, then put the front forks back on.

At that point I can clean the carbs and start er up again.

[steveo]

There's a few Brembo discs listed on UK ebay. Probably best to sit down before seeing the price tho. https://www.ebay.co.uk/itm/Honda-CB4...oAAOSw-4RaT6ZS

[jakejensen]

There's a few Brembo discs listed on UK ebay. Probably best to sit down before seeing the price tho. https://www.ebay.co.uk/itm/Honda-CB4...oAAOSw-4RaT6ZS

Whooo 250 Euros probably.... looks like they won’t fit anyways, if the picture matches the product. The 81 I have is a 5 bolt pattern.

[Cyorg]

It sounds disgusting.... always hard to diagnose via recording. If you are going to crank the engine over (with starter) with a plug removed, or run it on one cylinder to see if its one cylinder or the other making the noise... don't just let the unused plug lead hang there. Probably best to short it out to ground. If you are just turning it back and forth with a wrench, it doesn't matter. Doesn't sound like piston slap and that would be relatively rare in one of those engines. If something is going to go south due to lack of oil, the cam bearing surfaces in the head are first to go, so "usually" you'll get the death rattle in the upper end first. As suggested, set up the carbs, but before you do..... Adjust the valve clearances, cam chain, and don't forget to adjust the balancer chain. If the balancer chain adjustment has been ignored for a while. that could be a source of at least part of that expensive sounding racket. I would sort that out before you spend money on exhaust etc.

[jakejensen]

If something is going to go south due to lack of oil, the cam bearing surfaces in the head are first to go, so "usually" you'll get the death rattle in the upper end first. As suggested, set up the carbs, but before you do..... Adjust the valve clearances, cam chain, and don't forget to adjust the balancer chain. If the balancer chain adjustment has been ignored for a while. that could be a source of at least part of that expensive sounding racket. I would sort that out before you spend money on exhaust etc.

Boom! Thanks for the tips, seriously. I’ve got a set of feeler gauges coming in next week with a micrometer, so I’ll get it going. Time to tune!!!

[jcw]

Have you mentioned what you have done so far engine-wise?
Any bike i buy used, i will try to drop the oil pan and check for debris and clean out oil pick up screen.
Check air filter, change oil filter and check the plugs. Check the fuel filter and carb overflow lines. Drain the carb bowl and look at the color and smell of the fuel coming out. Check the plugs and wires. Look at the coils for any major cracks.
Check the carb boots, crankcase valve and line to airbox.

Address what you find then start in on tuning. Tuning is wasted on an engine not in good working condition.

[jakejensen]

Have you mentioned what you have done so far engine-wise?
Any bike i buy used, i will try to drop the oil pan and check for debris and clean out oil pick up screen.
Check air filter, change oil filter and check the plugs. Check the fuel filter and carb overflow lines. Drain the carb bowl and look at the color and smell of the fuel coming out. Check the plugs and wires. Look at the coils for any major cracks.
Check the carb boots, crankcase valve and line to airbox.

Address what you find then start in on tuning. Tuning is wasted on an engine not in good working condition.

Awesome stuff. I’ll do all that once i can start it again.

I havent touched the motor. I pulled The air filter foam which was old but not damaged... other than that I haven’t touched it.