Engine teardown

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Apr 15, 2004
Country flag
It all started as a simple oil pump servicing. But when I took the oil pump apart I found metal fragments inside. The pressure relief valve's piston had been heavily scored as well, so it was obvious the shrapnel had been all through the engine. Additionally, the mounting studs were loose. When I removed them I found out why - the threads in the case had been stripped. The trained ape who did that then tried to helicoil them and botched that too.

Our club had a Tech Day this weekend so I took the bike over. We pulled the motor and tore it down. The head is still assembled but everything else is apart including the crank.

We found more metal debris inside the sludge trap. The right crank journal is scored and will probably need grinding. Rod bearings are scrap. Right piston had seizure marks. Cylinder honing had been done wrong - circumferential pattern rather than cross-hatch. The rings were actually installed correctly though. They somehow managed to do that correctly. The pistons are the old bad ones with the slots in the ring land so I'd want to replace them anyway, even if they hadn't been seized.

The motor had obviously been apart before including the crank. Our best guess is a bearing came apart, maybe a rod bearing but who knows. They apparently tore it down and cleaned it out but didn't get everything. Then they put it back together, stripping out the oil pump studs in the process, and just ran it. No filter or mesh strainer in this motor so the crap went everywhere.

So, it's going to need:

case repair or replacement
new oil pump (gears are damaged)
new timing chain
new main bearings
crank journal grind
new rod bearings
new pistons
cylinder hone, maybe rebore
maybe some head work but don't know yet.

No wear at all on the cam and the cam bushings looked good too. So I guess that's something.

While it's apart I'm also going to open up the gearbox and have a look. This is also a good time to do the 520 chain conversion and service the rear isos. And have the sidestand bracket welded on (bike had the old "inboard" style sidestand bracket). And I'm thinking about other upgrades too.

One of the club members was riding a CNW bike. Wow that looked nice. But I think I can make mine nearly as nice for a lot less money. That's my goal...


Engines are *fun*, aren't they. Like a pinata you bust it open and get all sorts of suprises. And, if the bottom end's that bad - I'd make sure to have the head inspected as well (not yours - the bike's).

If you need a case, let me know. I've got a good spare 1971 case that's gathering dust. Ditto for the rods. Oh, and an oil pump - got one of those too.

Go for the automatic timing chain tensioner while you're in there. It requires the removal of some metal from the timing side case half and is best done with the engine apart.
Engine teardown

One of CNW's engine stands is really helpful as well.
Maybe I should have my head examined. But I don't think the pshrink could do anything to help me! :p

Welcome to the club Debby. I would like to say you are now one of the
" Elite " but too many of us have already been there. I have heard that story too many times about a bike been bought with a total rebuild having just been completed. Right !!!!!!!!

It will be a very good experience to build your own engine back up. When it is all done you should be a little more comfortable with what you have as far as reliability.

There are 4 more months until Christmas so it is not too late to be extra good. There is potential for some very nice stocking stuffers and the remainder of your list would fit nicely under the tree
PM'd you about the parts

That would be Norton Colorado. We're an INOA chapter although you'd never know it from their website :roll:

Norton Colorado

A lot of good people in that club! I was an active member for 10 years, but moved away in '02.
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