How in the hell did they build them on the assembly line?

Hi All,

Back in April a bought a 1981 CB750C as a project bike - when I bought it
it was leaking oil badly (per the seller it was just gushing out of the
head when the bike
was running, I never was able to get the bike started) Seller had tried
using RTV
(RTV?!?!) on the head to seal it,
didn't work, just wanted to get rid of the bike, I bought it cheap, etc.

So, last Friday I happened to be in a bike wrecking yard and asked the
owner
if he happened to have any CB750 top end parts. To my surprise he had an
entire 750 engine, sitting there, which he sold me for $100. (30 day
warranty,
and he claimed it only had about 20K miles on it, whatever, I wasn't
arguing)

So over Saturday I got interested and swapped engines. The wrecking yard
engine runs really smooth, (better even than my 1980 CB750K) bike has great
power, idles great, carbs were not all gummed up, life is good, etc.

What I cannot figure out though, after doing this job, is just how exactly
the factory BUILT the damn things! That engine took at least 30 minutes of
jogging around on the jack to get into the frame, I had to turn it at an
angle,
and many bolts had real limited acessibility. And to top it off, getting
the
carbs in was horrible. I had decided to keep it as stock as possible and so
kept the factory airbox - but there's barely enough clearance with the stock
airbox pulled back to get the carbs in, you have to reach in with long
screwdrivers
and such to get the boots realigned, and there's no way to apply pressure to
the center of the airbox once the carbs are in that will fully force the
intake
tubes completely onto the carbs, and the airbox of course bows inwards at
the center when you try to shove it onto the carbs. It took at least an
hour
of wiggling it to get it seated, and still the center two cylinders the
airbox boots
were not completely on the carbs. And that does not even cover all the
fishing around to get the airbox tubes and carb draintubes in the right
place.

I don't suppose that anyone reading worked in the Honda factory on
the motorcycle assembly line 25 years ago, but I would love to know
what the tricks were and how they did it.

Ted

 

I had two CB750s back in the 70's on which I logged a little over 300,000
miles. Yes, it was a little like a Chinese puzzle, but twist the engine
just right and it would slide right in. After a half dozen complete engine
rebuilds, muscle memory sticks with me like it was yesterday. After
removing seat, tank, carbs, etc., here was my technique for getting the
engine out: position a piece of 2x4 on a cinder block to the right side of
the engine, parallel and about same height as lower frame rail under the
engine. Place jack under engine for support, and remove all mounting
bolts/plates except for the long lower rear hanger bolt (just remove the
nut). Straddle the bike (where seat would be), and with right hand on head
to wobble engine slightly on the jack, remove long rear hanger bolt with
left hand. (Engine is now resting on jack and steadied with right hand.)
Move left hand under head, move right hand under clutch housing. Brace your
chest against frame backbone (where tank would be), lift engine slightly up
and rotate forward (head down/rear up) so rear mounting bosses on engine
clear frame protrusions, slide engine out the right side and rest it on
right frame rail and the prepositioned 2x4. Unstraddle the bike, left hand
under rear of engine, right hand under head, lift engine clear of frame.
Reinstallation was exactly reverse.

I didn't have the stock airbox on either bike, so had no trouble with the
carbs.

 

Bwaaahahahaha! Lovely.

There's a surprise )


<snip>

A lot of older Honda four-cylinder engines go in *much* more easily if
you remove the oil filter housing and sump first. If the bike has been
sufficiently stripped, the old dodge is to lay the engine on its side
on a piece of board or something, and lower the frame over the engine,
but that's not always possible if you're doing a simple swap with a
bike that's already built up.

Fitting carbs back on old fours is a right PITA, agreed. In the past,
I've used gentle heat (rags soaked in boling water) to soften the inlet
rubbers. Makes the job easier.

 

Oh yeah, I forgot to mention that they didn't bother removing the head,
they just smeared the RTV over the outside of the engine along the
head gasket seam. Blue RTV.

I'm just waiting to see what's inside the old engine. Since I never got it
started
it could be anything imaginable.

That's a good idea, I'll have to remember that!

Ted

 

I can't imagine anyone trying to seal a head gasket leak by smearing RTV
on the outside edge, to be honest.....

 

My uncle used to save his old worn out boots ,to make different gaskets
seal and even saw him make an bushing once that held til he got done
with what he needed the equipment for.
I miss that man he could do just about any repair with an old leather
boot ,wire and some electrical tape .He was a veteran from WW2 and drove
a deuce and a half in Germany those guys were amazing what they did in
the field for repairs we all can learn a thing or two from them.

 

Like this: the Wehrmacht had better equipment.