Topic: Possible cb750 1978 Purchase, But wanted your opinion first.

[robdrobd]

Hey folks, I have a chance to buy this bike. The bike has 27,000 miles and the owner said that after he allowed the last test drive the bike developed an engine sound/rattle. I was wondering if its worth it to take a shot, or is this rattle a possible big money fix. Any opinions would be appreciated. Here are some pics. I almost think its worth it in parts. Everything comes with it but the saddlebags. I was hoping it was just a cam chain or something, but I'd like to be prepared for worse case. Bike still drives and shifts through the gears.

[Rgconner]

Price?

Cam chain, out of sync carbs, needs a valve adjustment... could be anything.

[robdrobd]

What would be the worst case scenario ya think? Price - $1100.

[iron_worker]

Worst case scenario is a bottom end that is starting to go... but that seems pretty unlikely. The bottom ends of the SOHC 4s are known to be pretty stout.

Could also the valve train starting to eat itself. Lots of guys have plugged up oil ports with gunk and then burned up a head.

Could be just the valve train is out of adjustment... easy fix with a feeler gauge, a couple wrenches, and a flat blade screwdriver.

Could be the cam chain. You should ask the owner if he'll give you 5 min to try and fix it. You have to get the crank in the correct position (see manual ... you'll have to take off the points cover plate to see the viewing window) then loosen the locknut, loosen then bolt, tighten the bolt, tighten the locknut. Super easy.

I guess it could even be a main drive chain? Hard to tell from your basic description.

IW

[chewbacca5000]

Worst case scenario is a bottom end that is starting to go... but that seems pretty unlikely. The bottom ends of the SOHC 4s are known to be pretty stout.

Could also the valve train starting to eat itself. Lots of guys have plugged up oil ports with gunk and then burned up a head.

Could be just the valve train is out of adjustment... easy fix with a feeler gauge, a couple wrenches, and a flat blade screwdriver.

Could be the cam chain. You should ask the owner if he'll give you 5 min to try and fix it. You have to get the crank in the correct position (see manual ... you'll have to take off the points cover plate to see the viewing window) then loosen the locknut, loosen then bolt, tighten the bolt, tighten the locknut. Super easy.

I guess it could even be a main drive chain? Hard to tell from your basic description.

IW

IW if what your are saying about the top end eatting itself wouldn't it destroy itself rather quickly like in a matter of minutes?  Maybe the owner can take it for a 20 minute ride and robdrobd can follow along and see if there is a bike left.  If it runs at the end of that then I would go with cam chain.  If the owner does not want him to take a test drive or follow along I would pass.

He could also ask the owner if he tried to adjust the cam chain recently.

[flybox1]

get over there and hear it run....just dont fix it for the guy in his driveway 
1100 (hopefully with a title) is a pretty good deal+, but you could probably get it for $800.  make it sound like you're worried about the motor rattle, but are willing to take a $700 chance  see how he counters.
 i bet with a good battery and a complete tuneup, you'll have a solid runner.

[lucky]

The 1978 model had most of all the improvements in the engine of all of the CB750's
There were about 21 total improvements in the design.

I would go look at it and take a person that knows more about it.

[TrueSpin]

but you could probably get it for $800.  make it sound like you're worried about the motor rattle, but are willing to take a $700 chance  see how he counters.

Was thinking this myself.

[robdrobd]

Doesn't this bike look like its worth $1100 even if it has a death rattle?

[Jerry Rxman Griffin aka MuthaF'er]

Not likely that ONE test ride created a rattle. One test ride could blow it up then it wouldn't run. Miles aren't bad. It's probably been taken care of with all that #$%* that the PO put on it. ie not repeatly drag raced. Our bikes have rattles. Original equipment, just depends on the severity/where. Carb sync, clutch, tighten cam chain, primary chains. Most of these are exacerbated by out of sync carbs or bad tune up. Simple stuff. $1100 with a rattle! Offer $1000 without a rattle or $750 with a rattle. 

[Retro Rocket]

Carbs out of sync will make everything rattle. Cam chain, primary chain and clutch all rattle, doesn't mean they are screwed, as long as there are no knocks its all cure-able with little effort, it doesn't look like a bike that would have been flogged..

[robdrobd]

How would I recognize a knock vs. a rattle if I go out to look at this thing?

[Hasenkopf]

tell me where it is so I can  go buy it!   

[robdrobd]

Stay away... I got dibs

[fmctm1sw]

but you could probably get it for $800.  make it sound like you're worried about the motor rattle, but are willing to take a $700 chance  see how he counters.

Was thinking this myself.

+1.  Give one of those, "... I don't know, that sound could be the bottom end.  Whole motor would have to come apart..."  lines and see what he'll take for it.  That could be the case.  Like all those cars you see for sale that just needs the A/C "recharged."  The refrigerant had to go somewhere.  Maybe it's something simple... or maybe you need a new compressor, condenser and have leaky hoses...

[Stev-o]

Go test ride it. You will hear the difference of a knock or a rattle.  Most likely not a knocking, if it is, could be time for a major rebuild.

And it will look so much better with the fairing and sissy bar off!

[robdrobd]

Gonna head out to see it this week. Hopefully it is nothing major.

[robdrobd]

Without fixing this for him (because I want a good deal) I am going to look for the following things:

1. When I pull the clutch in does the sound go away - Clutch rattle
2. Cam Chain/Carb sync -not sure how to check for this so I may just hope my guess is correct.
3. Someone said if the sound goes away under load that is a good sign of an easy fix, if the sound gets louder it could be a bent rod or something. Sound right?


Anything else I can check in a 20 minute time period?

[chewbacca5000]

Rob,

Another 78 k has just appeared on the radar and looks to be in better condition.  It is a nice looking bike.  Been riding my 76 around and loving it!  PM sent.

[Duke McDukiedook]

There are no quick checks really, you would have had to work with these bikes for a while to know the ins and outs and know what sound is what to know if the engine is roached or about to be roached.
Take it for a test ride and see what you think or someone you know that knows about these types of bikes.
Odds are a single test ride would probably not create a serious problem but ya never know.

[robdrobd]

Hmmm. So if no power loss and shifts fine then grab it? If I can talk him down to 7 or 8 hundred I think I might grab it either way.

[robdrobd]

Ok, here's the deal. I checked out this bike and theres good and bad news

Bad news - every aluminum part is painted with spray paint. Headers, engine, forks, caliper, drum, etc. The head looks like it was sealed with some kind of gasket sealer and then painted over. Very bad paint job with tons of overspray. The tank is spray painted black and wasn't sanded well before painting.

Good news - bike runs strong, shifts fine, and starts nicely. Sounds like a cam chain to me and I didn't hear a knock. I would bet cam chain, valves, or carb sync. Gauges are nice, tires ok, seat brand new and nice, clean title.

Best news- this guy wants to part this thing out on Friday and said if he gets an offer of $500 before then he would take it. Guy looked to be pretty hard up and desperate.

He is in Oswego NY, his name is Rick. His number is 315-343-9384 if anyone is interested. 

[Stev-o]

So, it's a no?  Even at $500??

[DJ_AX]

What? .. $500 for a strong runner?!!!

[DJ_AX]

offer $300!

Wave a stack of 20s in his face!