'79 Special completely detonated at 85mph yesterday

phaedrus

phaedrus

XS650 Enthusiast
Messages
53
Reaction score
46
Points
18
Location
San Diego
image.jpeg
image.jpeg
image.jpeg
image.jpeg
image.jpeg
I was getting ready for the Distinguished Gentlmen's charity ride yesterday and was going through the bike. It has had a loud knock since I bought it a year ago so I was planning a big bore top end soon. Lost power at 85 on the freeway and towed it home. Look at all the insidey parts! I'm super screwed!! Anyone selling a 650 mill near San Diego?
 
The loud knock meant the PO tortured the engine.....................maybe ran it with low oil in sump, or maybe allowed the oil filters to plug up. In other words the PO did not do any maintenance, heard the knocking and sold it to you. You recognized there was knocking, but continued to ride until it blew up. Congrats..............both you and the PO have failed the "Basic Engine Maintenance Course".
 
Thanks for the kind words and sympathy on my sad day.

The PO replaced one (1) piston for some reason. I have replaced all filters and oil and worked on the bike for a year inside and out. The top end rebuild was waiting till finances could muster, but oh well.
 
Yeah, you won't get any sympathy from me. You bought a bike with an engine that had a loud knocking, but continued to ride it until the engine destroyed itself. Most guys would not buy an engine that is knocking, or if they did buy it, they would have promptly taken the engine out of the bike for replacement of worn out engine parts. Ignoring loud internal engine noises never has a happy ending.
 
Don't let anyone ever tell you that you don't know how to blow up a motor. You didn't go for just a little hole melted in the piston, you gave the old girl the full monty, lol. That being said, it does look like an over-heating/meltdown type event. What ignition? If still the points, timing could have been off on that side (too advanced), or the ATU could have been worn, allowing too much advance. Then again, it could be those fancy slide carbs not being jetted correctly.
 
Hi Phaedrus,
gotta say that I too have ignored that deep booming knock until the motor self-destructed.
And I too paid the price of negligence.
Luckily my bike got all the way home before it finally died because back then there
were no cell phones or bros with trucks so I'd have had to push it home.
Hopefully there's a motor in the classifieds that'll drop into your nice rolling chassis.
 
There is a recommended path to follow when buying and restoring/modifying old bikes:
First step............ check and re-build front and rear brakes, calipers. pads, M/C etc. so they work 100%
Second step........engine operation normal (no unusual noises) , carbs and ignition working correctly,charging system working 100%
Third step...........customize/ make the bike pretty/cool

Seems like many lads go directly to the third step. If budget is small, many can find money for the third step, but not the first two.
 
I am sorry for your loss, especially just before the ride. At freeway speeds, the splashing oil and sudden loss of power could have resulted in injury, so despite the motor melt you got home safe.
The bike looks well done otherwise; a motor or a parts bike will show up when you least expect it, you will be able to rebuild it better and change those little things that were bugging you.
 
Ouch, Could easily have been the exhaust rocker that caused the end. At 3000 RPM the piston goes up and down 50 times in 1 second. a dropped or stuck valve can do that to a cylinder before the engine screeches to a halt. Um, all that aluminum looks pretty dry, once the piston goes, crankcase pressures from the other side going up and down usually blows oil everywhere...... So yeah watch for a "decent" engine nearby. A wanted in the local CL often gets you a couple of leads. Makes more economic sense than a rebuild. But you might want to do at least a top job on it, open and inspect the filters and oil pump before installing, no matter how much the seller swears "it's just like new".
Always sucks to receive an education by "experience". Yes I've had my fair share of those.
 
Here's what the engine had done to it:
PMA
PAMCO ignition
Mikuni VM34 carbs running safely rich and synced at one time
New carb boots
Temp gauge oil dipstick- it never went over 150 on that short run
Topped up with Rotella within the week
...An ignored knock till funds could provide the top end rebuild to the JE pistons at 700cc
 
lakeview said:
At freeway speeds, the splashing oil and sudden loss of power could have resulted in injury, so despite the motor melt you got home safe.
.
Click to expand...
Yes I do feel lucky that it was just a gradual loss of power and I managed it safely.
 

Similar threads

Muckroot
XSJohn's right side hotter theory - explored
2
Replies
21
Views
3K
xjwmx
xjwmx
Back
Top