Possibly entering the 378 club!

Sderbyshire said:
This will be my approach, minimise disruption and chance of putting it back together incorrectly!

What’s the liklihood of case bolts breaking when i undo them?
Should i reuse old bolts or buy new?
Anything else to worry about?

Steve

there was a thread (a very detailed thread) on the hondatwins site back in 2012 or so, never finished and the guy disappeared but he broke several of those case bolts, I would be prepared for it and take it slow, considering that is must have been done in the past - since someone put a bolt in the tensioner arm, I would say be on the lookout for other things inside that may be improperly installed or missing
 
So, valves arrived yesterday, from israel in 5 days !!!

Still awaitng the cam sprocket and bolts.

I’ve decided that although the cam tensioner is clearly ‘modified’ it has been working fine for the 3 years i’ve had the bike so am going to put off separating the crankcases and get the motor running.

I want to see how it’s working in 389cc configuration and then address any issues at the same time as the tensioner over the winter. There have been several bodges on this bike that have come to light during my ownership, so to be honest i dont want to uncover anything else in the crankcase unless i have to !

Watch out for updates when the sprocket and bolts arrive, hopefully this week.

Steve
Ps, shall be loctiting and tripple checking those pesky 7mm bolts !
 
I never loctited mine and I'm just crossing my fingers everything inside there doesn't explode.

I already got a scare when I left the points advancer/cam bolt off and the bike jumped ignition timing, back-firing loudly before dying the very first time I started it up...
hope that is all the scare for my bike!

as for opening up cans of worms - yea save it for the winter!
 
Case bolts should come out pretty easy. Never had a problem re-using them. It may be a good idea to get a flat punch and 'shock' them with a sharp smack before trying to unscrew though. I've done full stip, all mods, new cam chain and tensioner 'horseshoe' in about 10 hrs (from bad runner to good runner, engine in and out etc) Not sure if I could do it as fast today though as arm and back are pretty messed up plus I'm 10 yrs older ;D
 
Pretty sure I use a couple of taps with an electric impact to break them loose on both the CB360 (I had to split the cases like 3 times on that bike ;D) and the XL, haven't broken one yet.

The small taps are better than a breaker bar with a lot of leverage IMO with those long collared case bolts. In any case they aren't torqued very high so they shouldn't take that much force to break loose.

That being said if you haven't had any issues with the tensioner I wouldn't even bother messing with it.
 
In the absence of engine parts, seem to be coming from the us to the uk by donkey...... i thought i’d tidy up the tail end and do some badge engineering :)

The 70mm pistons equate to a displacement of 389.4cc which is pretty close to 390cc..... and a 9 is an upside down 6.......

Careful work with hacksaw and dremel and we have a CB390 !
 

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Arty garden shot......
 

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How cool is that! I have thought about modifying the cylinder badge by making it say "376" but thats ok... I'll stick to explaining (bragging) that it's really a 380 anyway
 
It's traditional to go to nearest number rather than actual capacity (CB400f was 406cc, Z1 903cc, etc)I like the badge idea and wish I'd thought of it. Bike looks purposeful with 550 front end and dual disc's 8)
 
crazypj said:
It's traditional to go to nearest number rather than actual capacity (CB400f was 406cc, Z1 903cc, etc)I like the badge idea and wish I'd thought of it. Bike looks purposeful with 550 front end and dual disc's 8)

true true, but the engine casting says 356, actual capacity. I'd stick with 380 otherwise
 
Parts delivery !.......
 

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The CB390 Lives, again.

Installed the new cam sprocket and bolts ( triple checked amd loctited :) )

Set cam, valves amd timing and he fired right up.

Couple of cautious test rides and all seems good.

Any advice on ‘running in’ for the big bore engine?

I ran gently up to 7k, as i dont usually have a tacho on the bike, just a speedo, this sounded quite fast enough!

Steve
 

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First up, just idle the engine until it's warm.

Then you need to take it out and ride it as soon as possible. Don't rev the engine without load on it.

When riding, rev the bike up to 5,000 RPM in first gear and then let off the throttle and let the engine do the braking. Repeat a few times.

Repeat again at 7,500 RPM.

Now take it out and ride it like you stole it. Avoid staying at the same engine speed all the time; use the whole RPM range.

It should only take 20 miles of riding or so to break an engine in.
 
What he said, but if you have good hills around you use them for engine braking. Full throttle, off throttle, full throttle, off throttle. In a way, you're trying to put compression on both sides of the rings to seat them.
 
I ran my first 378 on a dyno to about 11,500rpm 30~40 mins after building it. It only had a quick ride around yard and a coupler of heat cycles. :eek: Having it under load for a few seconds after first start helps rings bed in faster but can cause piston to 'pick up' if your not 'careful' ;D
 
Thanks Guys

I’ve done a small run at varied revs up to 7k.

Tonight i’ll do a more methodical load/unload run building up the revs.

Then i think i’ll recheck valve clearances etc and go for an Italian Tuneup :)

Steve
 
The CB390 is running well!

Engine seems stronger than before, but i do need to build up my trust in the motor, I built it !, before proper testing.

Will finish running in this week, then retorque the head and reset valve clearances, seems a little tappy to me.

He he is, resting after a test run :)
 

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So tonight i thought i’d retorque the head, check things over etc.

Head bolts all just clicked on the torque wrench, so hadnt loosened at all.
I reset the valve clearances, timing and fired him up, oil pissing out of the points cover.
So i put the cam seal back in...... and tried again !

Wow! Running like a sewing machine and pulling much harder than before
Clutch is slipping in third when the engine comes on cam, i had to put the standard springs back in as my ‘hd’ ones were shite.....

Two questions for the learned 360 folk?

1, can anyone supply me a set of genuine hd clutch springs, i’ve had no luck getting some
2, whats the procedure for dynamic timing the engine, ie at what revs and what advance am i seeking ( i have a timing strobe and know how to use it from my TR6)

Thanks for all the help so far guys, its been a fun upgrade project.

Here’s the CB390 waiting to go out for test ride......

Steve
 

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