1974 Commando 850 Barn Find

elefantrider said:

Yeah, dare I say never but IMO, there is no way that frame is ever going to be straight.

Reminds me of the effort behind this famous article.

https://nortonclub.com/docs/Straightest_Commando_Frame.pdf

Click to expand...

"Straight enough" is often the goal.

"Straightest" is nigh on impossible.

That's a win if the bike tracks straight down the road and the license plate, rear fender and tail light are all on straight. Many are not.

That's kind of unfortunate the Commando doesn't have a removable/replaceable rear subframe, although it looks like that wouldn't help much in this case.

I had to replace the main frame on my 1972 manufacture 750 Commando due to internal corrosion. I purchased a new main frame from Andover and had it at my door in less than a week . Powder coated black and the cost was likely less than welding in new tubing and refinishing. Highly recommended.

Richard Tool said:

I had to replace the main frame on my 1972 manufacture 750 Commando due to internal corrosion. I purchased a new main frame from Andover and had it at my door in less than a week . Powder coated black and the cost was likely less than welding in new tubing and refinishing. Highly recommended.

Click to expand...

So new AN frames are UNPAINTED???

grandpaul said:

So new AN frames are UNPAINTED???

Click to expand...

Powder coat black

Richard Tool said:

Powder coat black

Click to expand...

Ah, I mis-read the original post.

As Emily Litella (Gilda Radner, RIP) said, many times... "Never Mind!"

A new frame would be nice, but not in the budget at the moment. I'm trying my hand at a repair before moving on to replacement.

In the meantime I'm working on cleaning the rest of the parts and starting to rebuild. I've got the top end cleaned up and lapped, just waiting for new tappet adjusters as the old ones had been overtightened and the threads messed up. Transmission has also been stripped and all bearings replaced. Just waiting to be put back together this week.

I also tried a new method of rust removal on the gas tank. I've had success with Evaporust in the past, but don't want to pay $100 for enough solution to do an entire tank. A few months back I ran across a video of a diy version that used citric acid and washing soda to create a similar sodium citrate solution. I know everyone swears by their particular brand of acid/electrolysis/voodoo, but this one did a great job with a lower chance of further eroding the base metal or damaging the paint. The steps I followed are below.

In a 5 gallon bucket, add 15 Liters of water. Mix in 1500g of citric acid crystals(I bought a 5lb bag from eBay for $20 delivered). Stir until dissolved. SLOWLY add in 600g of washing soda. The mix will foam up so take your time and let each addition react. Once finished, add some dish soap to act as a surfactant. I probably used a bit more than 1/8 cup, which is too much.

For the tank, empty any remaining fuel and pour in a small box of drywall screws, couple liters of water, and a half cup of simple green. Shake the tank for 5 minutes in all directions to try and dislodge any loose rust. Empty the tank and fish out the screws. Rinse a few times to remove rust flakes. Once empty, fill completely with the rust remover solution.

Wait a day or two and check your progress. After a day you will see the small rust spots disappear, but some large ones remaining. You'll know its ready when the large flakes easily detach when poked with a stick. Empty the tank 3/4 of the way, keeping the solution in the bucket for the next project. Swish the remaining solution around before emptying to remove larger flakes. Rinse repeatedly with water, drains completely, and dry with a hair dryer on low. Once dry, either fill with fuel or use some type of oil on the interior to keep it from rusting again.

Before and after of the inside of the tank below.

Nice, I once labored over an old sportster tank, sanding, filler, decals, clear coat like glass. Guess it was a little worse inside than I expected, muriatic bubbled right through into the paint..never again. Thanks for the recipe.

Richard Tool said:

I had to replace the main frame on my 1972 manufacture 750 Commando due to internal corrosion. I purchased a new main frame from Andover and had it at my door in less than a week . Powder coated black and the cost was likely less than welding in new tubing and refinishing. Highly recommended.

Click to expand...

I agree. A few years back, I had a customer MKIII with sidestand lug collapse problem. The places willing to fix it costs a lot and they required the frame bare. A new AN MKIII frame and some of my time and he was good to go. I had zero problems with the new frame - everything fit well.

I've also done other frame swaps with used frames found on eBay. There are several available now, but they are priced too high - it takes patience to get the right deal.

I went in to the shop fixing the frame this week and confirmed that it seems to be straight enough to use. All of the measurements in the book checked out and the headset also seem perpendicular to the iso mounts. They think it should be done beginning of the week.





In the meantime, made some progress on cleaning up parts and took some steps back dissembling the bottom end. I didn't intend to go that far, but was having a hard time really cleaning the sludge out of the sump and decided it would be best to just split the cases and the crank in case the same buildup was inside. Seems like a good call, the inside of the crank was a bit dirty and the big end shells don't look great to my eye. I left my mics at home so couldn't check the journals, but they felt fine and didn't seem scored or pitted. Pretty sure those tabs are supposed to be bent over the crank bolts though.

Also, are FAG roller bearings stock for this crank? These seem a little too new compared to the rest, I'm thinking they've been replaced. Ideally I'm going to leave them all intact and run them.






The camshaft also doesn't look great, not sure if I should be concerned by this wear pattern or not? There are a few small pits too. GME has a few cam options I may consider if this one is fubar'd. Unfortunately would need followers reground as well so not ideal.

Hammerski said:

I went in to the shop fixing the frame this week and confirmed that it seems to be straight enough to use. All of the measurements in the book checked out and the headset also seem perpendicular to the iso mounts. They think it should be done beginning of the week.

In the meantime, made some progress on cleaning up parts and took some steps back dissembling the bottom end. I didn't intend to go that far, but was having a hard time really cleaning the sludge out of the sump and decided it would be best to just split the cases and the crank in case the same buildup was inside. Seems like a good call, the inside of the crank was a bit dirty and the big end shells don't look great to my eye. I left my mics at home so couldn't check the journals, but they felt fine and didn't seem scored or pitted. Pretty sure those tabs are supposed to be bent over the crank bolts though.

Also, are FAG roller bearings stock for this crank? These seem a little too new compared to the rest, I'm thinking they've been replaced. Ideally I'm going to leave them all intact and run them.

The camshaft also doesn't look great, not sure if I should be concerned by this wear pattern or not? There are a few small pits too. GME has a few cam options I may consider if this one is fubar'd. Unfortunately would need followers reground as well so not ideal.

Click to expand...

Polish the crank, shitcan the cam.

Also, what looks like a tab washer is really just retaining a dowel pin between those bolt holes.

cam is now a paperweight

+1 on the above..

Journals should polish up fine.

Replace the shells.

Mains should be fine at that mileage, clean and inspect to be sure.

Cam is not usable, but could be used as a core to send to Web Cam or similar (build up with stelite and re profile).

Surprised the cam ended up in that bad shape in only 5 k miles.

When I build an engine other than standard I measure the spring compression poundage and check for coil bind. On a street bike no more than 180 lb over the nose and 100 thou minimum off coil bind at full lift.

Then if the bike sits for more an a week or two I take off the exhaust rocker covers and pour an egg cup of oil down the push rod tunnels before starting.

Finally I don't let the bike idle until it's warm and set the idle at 1000 to 1200 rpm.

Plus obviously use a suitable oil with zinc and change it at 3 to 4 k intervals or at least once a year.

Cams and followers have lasted many tens off thousands of km on the street.

Cam, big end shell, and hardware are en route from the UK. In the meantime, finished painting most brackets and got the frame back from the shop. Time will tell, but everything lines up so far. Also finished rebuilding the trans so I threw it in the frame. Z plates will need to come off, but put them on temporarily to get the battery tray in. The left side cover mounts were bent in whichever accident caused the frame damage and needed to be aligned. Everything fits up nicely now.

Enjoying this... You don't fool around! Nice work.
Russ

Getting closer...

Oil lines and tank in, brakes rebuild and bled, front fork final assembly done, wiring harness done(redid the reg/rec section, grounds, and removed anything not needed, added battery monitor and blade fuse at battery negative), engine mounted, bars and some controls on, both side covers fit and ready to mount, rear grab rail back on.

If you installed the bottom bolt in the oil tank, REMOVE IT (unless you are OK with a cracked tank).

Just keep an eye on the two rubber bobbins and replace them as they fatigue and crack.

Open intake ports with washers and screws nearby, scare me...

grandpaul said:

Open intake ports with washers and screws nearby, scare me...

Click to expand...

Even better when little people help.