Something went snap...or pop...

[LukeM]

I was riding the bike ('79 CB750L) home from an appointment. Nothing special, riding like I always do, and at 35 mph, the bike makes this snap noise, and loses power.  I coast to the nearest parking lot, and try and restart it.  The starter spins the engine pretty freely, and it doesn't fire. As far as I can tell, it's getting spark (it backfired once or twice while cranking). My first guess is broken cam chain (maybe the long one, maybe both).  I think the best way to diagnose this is a compression check on all cylinders.  I intend to rent a motorcycle mechanic to come check it out.  I figure a $40-50 diagnostic fee isn't too bad.

It has had a bit of a rattle for a little while now when idling.  I adjusted the cam chain tensioners per the manual a couple of weeks ago, with no discernable change in the rattle noise.

So let's assume it's a cam chain problem.  How far apart do I have to tear the engine to replace it/them?

Any help is greatly appreciated.
Luke M

[LukeM]

Well, my original diagnosis is correct:  broken long cam chain (between crankshaft and exhaust cam).  I found a good mechanic, who admitted he's better with Harleys but does work on Asian bikes.  I did most of the disassembly (tank, airbox, carbs (which I cleaned out later tonight..hope I got everything cleaned), cylinder head cover, final drive, and then had to take the car back home for number 2 son.

So, another 6-8 bolts, and the engine should be on his stand.  He's thinking some intake valves may be bent, and will check it over and add stuff to the "as long as we're tearing the engine apart" list.  Luckily, I have a friend/co-rider who gets a sizable discount from a Honda Powersports store, so hopefully parts won't be too bad.  The MC mechanic is charging $30/hour.

I was really surprised how easily the bike comes apart. The only really tough part so far was getting the carb bank out.  Turns out it's easier to pull the boots from the airbox.  Then it just slides right out.

Here's a pic of the broken chain.  I figure it's the factory chain, and after 31 years, it was probably about due.  Still need to check the chain tensioners and make sure they work.

Luke M

[wvhardtail]

Ugh, that sucks. I am very to lucky my best friend is a mechanic. He doesn't charge me money but I am fairly good with a wrench so I mainly use him for advice. Plus we ride together so that helps. Only hard part about my engine (SOHC) is that it's a b*&^% to get out of the frame. Good luck!

[free2ride]

where's the crying smilie?

for you . . . nd the bad luck. at least it's nearing the end of the season . . . last year I took my bike in [for an oil seal replacement] in May and didn't get it back until the end of August [stinkin' hard-to-get parts].

oh . . . I'm crying for me, too. $30 an hour? I'm at $85. I'd say it's because he specializes in old bikes, but Honda's [actually, all ofthe local MC shops] mechanics charge $90!

get 'er together soon.

[LukeM]

Contingent on my getting the bike back in April, I had budgeted between 500-1000 USD for repairs.  That would put the grand total of the bike to about $1500, which is what it's worth on the open market.  No sad smiley face yet, unless the bill goes WAY over a grand.  Then I'll cry.

I did undo the main parts of the carbs and cleaned them out nicely.  #4 was the one that had the shiny black spark plug, and I thought it was the one dumping raw fuel into the cylinder.  It didn't look any different than the others.  All jets and passages were clean. There was a little buildup of crud in the float bowls. I guess when we get the head off we can investigate valve guides/seals and so on. The mechanic has a good machine shop at his place, and should be able to get things going pretty quickly.  I'm in no rush, and neither is he.

Updates to follow.
Luke M

[mikey440]

 Luke, sorry to hear that you lost a camchain, makes me wonder about mine, my bike has only 12,000
 miles and it makes a rattle on idle but its the clutch as all these bikes do, I hope your mechanic gets it all straightened out for ya, at least you wont have to worry about a camchain next time your ridin,,keep us posted,,mykee440

[mikey440]

 Luke, that bike you have is worth every penny, its a classic,

[LukeM]

Well, the Avenger has 34000+ miles on it.  I'm reasonably sure it's the factory chain. It's Paul's opinion that the exhaust valves were bent and they may have gotten stuck, which put a large load on the cam chain.  Sounds logical.  Or maybe it was just old.
 
Latest info: we've had 2 of the cam journal bolts break, which means they'll need to be extracted.  It shouldn't be that bad.  So far, we'll be getting the long and short cam chains replaced, 1 or 2 exhaust valves in cylinder #4 replaced, and the BIG gasket kit for this motor.  If all goes well, it'll be operational sometime next week.

I figure I've got a parts bill around $400 or so, and maybe another $500 in labor.  I'm doing some of the work, which is helping to defray Paul's $30/hour rate.

On the "keeping it" topic, I've had a lot of fun riding my wife's Honda Metropolitan while the Avenger is down.  Granted, it only does 38 mph max, and it's Creamsicle Orange, but I can't argue with one kick starting, and twist and go.  It's got more storage than my bike.  I was thinking of trading in the Avenger when it's running good for a Met or an Elite or Ruckus, but if I put that kind of money into it, I might as well enjoy a good-running bike, right?  

Luke M

[Re-run]

those little skooters are nice around town for the most part. I would get a ruckus as I think they do at least 50. Only downside is when you twist the grip and you just start moving as opposed to revving and dumping and hanging on with a huge grin!

[wvhardtail]

You know what they say about scooters.....?

[LukeM]

OK...finally got the engine down to the crankcase halves.  2 days of solid work.  I will say this: I hope I never have to do this ever again.  There are WAY too many bolts involved in holding this beastie together.  I needed both the Haynes and FSM to get it apart. There were all sorts of metal bits in the crankcase, most from the sheared up cam chain.  

The long cam chain tensioner is mostly worn away and will need to be replaced.  The chain must have been loose for a long while: it was wearing away the aluminum at the case where the crankshaft gear is. I will also swap the short cam chain as well. Pistons look fine, aside from some carbon buildup.  The bores on the jugs look fine, but my mechanic suggests new rings. We'll swap out rod and big end bearings, because they're just starting to show some copper. The primary chain looks very good, so if I don't have to swap it, I won't.  I do have a budget to adhere to. I think that's enough to get this engine rebuilt.

Now it's off to the dealer man (or maybe Rice Paddy) to see how much these parts are gonna be.  This might get painful, but hopefully it'll run a whole lot better when it's all back together.  I have to look at the end result, or I'll get disappointed at the inbetween steps. :-)

Luke M

[LukeM]

OK, I'll bite: what do they say about scooters?
Luke M

[wvhardtail]

HOLY HELL, DON'T GO THE STEALERSHIP FOR PARTS!!! I feel your pain. Finished my top end last weekend and that was quite enough bolts for me as well! Good suggestions on the ring, too.

Oh and scooters are like fat chicks, both fun to ride til your friends see you on one!

[free2ride]

LukeM wrote

Contingent on my getting the bike back in April, I had budgeted between 500-1000 USD for repairs.  That would put the grand total of the bike to about $1500, which is what it's worth on the open market.  No sad smiley face yet, unless the bill goes WAY over a grand.  Then I'll cry.

I'm looking at my bill for last year's work and the tears are starting to fall . . . I knew it was going to be expensive but had too many hours of labour to fix the thing [I'm clueless and trust the mechanic] . . . was looking at a bunch 'cause the motor had to be split to change the bottom oil seal but then the bearings were basically shot and the clutch needed work and the brakes and [tears tears and more tears].

That was just last year's work . . . carb job the year before . . .


BUT: this year I've been out as often as possible and it looks like it is going to be a good fall.

Sure I could have almost paid for the bike I originally wanted before I got this "deal" . . . but the bike runs beautifully and it gets looks. I'll never get what I've got into it out of it but that's OK -- it should [fingers crosses] last many more years before anything serious goes [got away without tires this year but not next] . . . and I'm ready to start trying to do some work on my own.

All that to say . . . I'm  when I'm on the bike and I've just decided to ignore how much it cost to fix. Sure I couldn't really afford it . . . but I knew going in that I probably couldn't afford a bike and bought it any way.

Again, hope the repairs go well and smoothly.

[LukeM]

Thanks, Free.  I think I'm getting a good deal as far as the labor goes.  The parts are going to be the pricey part.  I've got a line on a used engine in the Columbus area for $150, which I could scavenge for parts like valves, or maybe the whole head.  I have no idea what shape this used engine is in, but hopefully I can recycle some parts.  If all else fails, it'll be nice to have the "whole" engine there for a reference.

I'm sure the end result will be well worth it, and if I get a few more years out of this beastie, it'll be worth it.  It's in good enough shape, and the mechanic's friends that stroll through his shop go out of their way to say how nice it looks, and how good a shape it's in.

Luke M

[LukeM]

I have a friend who works the MSC program at the Honda dealer in Newark, and I'm remembering he can get a 40-50% discount on parts.  So, that should help, along with quicker turnaround assuming the dealer has all the parts I'll need.

I've been reading horror stories about the sad state of replacement cam chains.  I'm not a high revving guy when I ride this bike. Well, not all the time...once in a while I'll get it up to 5-6K rpm. I leave the high winding shenanigans to the crotch rocket riders who need to prove out their manliness...errr...compensate for a shortness somewhere...errr...you know what I mean.

Luke M

[free2ride]

LukeM wrote

I leave the high winding shenanigans to the crotch rocket riders who need to prove out their manliness...errr...compensate for a shortness somewhere...errr...you know what I mean.

[wvhardtail]

I agree! I like to ride but I also like LIVING!

[LukeM]

Thanks to the people at Rice Paddy, I was able to pick up a slightly used pair of cam chains, the primary chain, both cam chain tensioners and guides for about $40.  The old tensioner has almost no plastic on it.  This may have hastened the failure, as the chain was loose regardless of tensioner tightness.

I also picked up a bare cylinder head, just in case the mechanic wants to move the valves and stuff from one to the other.  The original head doesn't look that bad, but 2 of the cam bearing bolts broke and may be a problem to extract.  Also, Rice Paddy may have a fully populated head in their warehouse for a few dollars more, so I may go that route.

I'll still have to hit up the dealer man for rings, crank and rod bearings, the BIG gasket set, oil seals, and 2 exhaust valves. Need to check the jugs to make sure they don't need to be bored out. However, I do know a guy who gets 40% off of dealer price.  I figure that's not bad at all.

So I got an email from another poster, wondering why I was pouring this kind of money into this bike.  Well, I started with $500.  New tire and some little stuff was another $100-150 or so. Current resale value on this bike is anywhere from 1000-2500 depending on condition.  I couldn't sell it for $750 in the shape it was in: I figured the motor was hurt pretty bad, and since I don't like getting stuck like that, I try not to stick others like that.  Call me old fashioned...  So, if this overhaul runs to between 1000-1500, is that too much to put into this machine?  Everything else on the bike is in good shape: clutch, carbs, tires, brakes, chrome, paint, seat, bars, frame...might as well keep it, run it until it explodes.  Parts are getting harder to find, and those that are out there are getting pricey.

Comments?
Luke M

[free2ride]

LukeM wrote

So I got an email from another poster, wondering why I was pouring this kind of money into this bike.  Well, I started with $500.  New tire and some little stuff was another $100-150 or so. Current resale value on this bike is anywhere from 1000-2500 depending on condition.  I couldn't sell it for $750 in the shape it was in: I figured the motor was hurt pretty bad, and since I don't like getting stuck like that, I try not to stick others like that.  Call me old fashioned...  So, if this overhaul runs to between 1000-1500, is that too much to put into this machine?  Everything else on the bike is in good shape: clutch, carbs, tires, brakes, chrome, paint, seat, bars, frame...might as well keep it, run it until it explodes.  Parts are getting harder to find, and those that are out there are getting pricey.

First, big thumbs up for not sticking it to someone else.

As to how much to put into the bike, if you're asking me you're asking the wrong person . . . I've already done my whining regarding how much $$$ I've got into mine . . . coulda walked away and bought something newer but my mech said that you never know how a bike will turn out, and with the work in mine I have a good number of years left . . . plus I have a bike that is not run-of-the-mill ordinary/like very other bike on the road.

I say go for it, merely because you'll know the bike you have and you won't get better for the money you put into buying something different.

my 2¢