teardown for a rod knock.

angus67

angus67

Welder's penetrate deeper!!
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hi guys, bad news.
If you've been following along with 71' restore by angus67< than you know where i am on that bike.
owner came by yesterday, and since I wasn't familiar with the situation to which it was garaged for 20 years I didn't know the condition existed.
He overheated it in 92, racing it, engine became clattery. new pistons, rings. he couldn't get it started then. sat in his garage for years. I, being the younger guy into tech(read: Internet) I found you guys. he said get it running. its his dad's bike with 3k miles on it.
I did that . big thanks to Pamcopete. Runs sweet! Steady pull threw idle/pilot/mains.
Unfortunately, the noise that prompted him to give a new top end to the '71 motor.
is unfortunately still there. . He is VERY detail oriented ,and has pinpointed the noise to the lower half of the engine. pitch of noise changes from the rite side cover to about where the top end (fins) starts. We have agreed it has a rod knock..
what is involved here? can we split the case, pull the pistons out of the jugs without dismantling the top end? what needs to happen? where do we go? Punkskalar( or anyone willing to sympathize)What can we do to quiet this bugger down? It runs great, but sounds awefull. should we run it? or will running it be more harm than good?
What kind of moneys we talking here? I think I know I need to separate the con rods form the crank, install new bronze, and what-nots.
I just need a direction. whats involved? can he putt around on it? Can I put a lower mileage crank assembly in it?) I did that with my '80 for 80$). Thanx again everybody who helped on this bike. :shrug: I really don't want an engine-less frame haunting my garage while I'm trying to do a clutch job on my 2003 marauder.
 
Running it will just make it worse, you dont want bits of bearing floating around the bottom end. I had a right side crank bearing go bad, but just replaced the whole engine with a used runner(lots cheaper than replacing all the lower end bearings). Since it is a 71, it may be a good idea to keep it original and spend the money on a complete rebuild.
 
thats what I' thinking too, but he test rode it, and revved the hell outta it, Ive got some hefty inclines around my house, and he said it never ran better.
can It be taken apart from the underside without disturbing the top end? I think so, but want to be sure. How would one get the rings back in the bore? thats the only hang up i can think of at this point. Well,, another point...
where can I find a early low mileage crank assembly?
 
Wow what a blind side hit on you. Oh yeah, by the way it had a death knock when I garaged it 'cause I over revved it??:banghead:
 
Don't be surprised if he sells it a couple weeks after it's all done.
 
At least it runs now.
I did service) clean ) the upper oil filer. the usual crud.nothing big there. Ide feel really bad If I was a shop, and charged him the headaches and hours that went along with that bike just to end up being the same.
On a side, He gave me a nice golf club set for my time, gave it to my dad for something for us to do this summer, but some jerk broke in to my dad's garage and swiped it, along with gramp's clubs, and a 18horse johnson.
 
check ebay for a bottom end, but you still really dont know the true condition. A new bottom end bearing set is going to cost at least $500 counting gaskets and misc crap needed to get the job done.
 
Money has been known to get tight all of a sudden. I'd make a deal where if he sold it I'd get paid for my work. Damn I'm cynical....
 
 
not looking foward to this.
How do I know those rods are good? I might have to trek up to WISEGUY CHOPPERS FOR A CRANK ASSEMBLY.
Marvin's got Alot of bikes at his house.
I need to see them in person to tell.
good prices on those though if good.
 
yeah thats just the thing, you really dont know till it is in your hands. Marvins a good guy, I would buy one if he has one.
 
that's where i got my assembly for my '80, before the shop openned, and he was working outof his two car garage. the two in one intake was still in R&d.
 
Being a 71 it has the 256 engine. Well known for rod small end trouble. The small end of the rod has a needle bearing. The rod small end tends to get egg shaped under hard use.
Climbing steep hills at 75 mhp would fall into this catagory. Spending too much time above 5000 rpm can do it too.
I don't think the pistons can come down out the bottom.
Replacing the engine internals from a 447 engine would probably be the best thing for it. The rods don't use the needle bearings and the rod small end is stronger than the 256 rods. It would withstand the abuse better.
 
Angus, trying to get the crank out without taking down the top end won't buy you anything. You can break the cam chain and remove the pistons and rods with the crank, but you can't get the pistons and rings back in the cylinders without removing the cylinders first, and cylinders should be honed before pistons and rings are reinstalled anyway.

Next, you don't "replace the bronze" in these motors because there isn't any; the rods are one-piece and ride on roller bearings, and to replace the rod bearings the crank assembly must be pressed apart.

Finally, if you get a crank assembly, be sure the rods on it have 22 mm. wristpin holes, not the 20 mm. holes of the late engines.

Rod bearings come with the rods, and they go for far less than $500/pr. unless you want Falicons or Carillos or suchlike trick stuff. The main bearings are the costly items, and at this point there's no reason to believe the mains are trashed (but little reason to believe they're not).

I hope you're getting paid for this--good luck!
 

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