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'71 750 Commando Rebuild

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Re: '71 750 Commando Rebuild

Postby ELMZY » Fri Jul 15, 2016 11:35 pm

Engine Trouble.
Image
This original slotted piston may not of "flipped it's lid" as some are reported to have done (above).
But it did drop a piece of skirt (below).
The importer drained the crank for transport so I was surprised to find it - in the timing case.
There aren't many passages into the '71 timing side so the odds were pretty high.
Image

Image

Image
Evidence of a few rough revs around the crank (above).
I'm guessing this breakdown was a long time ago by the 13,000 miles on the speedo.
And the condition of the crank journals (below).
They've held their shape and are within spec for a new set of standard bearing shells - and new crank hardware.
Image

Image
Some black cheese in the sludge trap (above).
I was expecting more, considering it ran without an oil filter.
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Re: '71 750 Commando Rebuild

Postby grandpaul » Sun Jul 17, 2016 9:07 am

Photo links are screwy.

There is no way to get piston debris bigger than about 1/4" into the timing case, unless it involved tools and fingers.
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Re: '71 750 Commando Rebuild

Postby ELMZY » Mon Jul 18, 2016 10:20 am

"There is no way to get piston debris bigger than about 1/4" into the timing case, unless it involved tools and fingers."

Tools and fingers ? WTF ?

That negative inference surprises me more than that piece of metal I FOUND down near the oil pump.

But thanks for the heads up on my choice of Image format.
It seemed like such a good idea at the time.
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Re: '71 750 Commando Rebuild

Postby grandpaul » Tue Jul 19, 2016 5:26 am

I'm just saying that any metal in the timing chest would have to fit through the transfer hole(s) which measure around 1/4" (3/8"?)

Nothing implied or inferred.
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Re: '71 750 Commando Rebuild

Postby ELMZY » Tue Jul 19, 2016 8:20 pm

Last few frame mods before a visit to the powder coater.

Had the later model side stand lug welded on (Old Britts Tech Article).
Still a couple of crimp marks on top of the tube where the PO had the double U bolt aftermarket lug attached.
The worst ones were underneath so I got the welder to fill them in.
Upgraded side stand lug.

Bought a new swing arm with the gusseted cross member from AN, and had the plug housings machined a little deeper to suit the MK 111 shorter bushes and lube disc/welch plug set up (Old Britts Tech Article).
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Re: '71 750 Commando Rebuild

Postby ELMZY » Mon Aug 08, 2016 8:49 am

Finished the crankcase breather - thanks Matt for the kit and comnoz for the engineering know how.
Tapped and blocked off the redundant passages into the timing side with 2 x 3/8" UNC + 1 x 1/4" UNC black socket head grub screws.
Drilled a 1/4" hole for drainage back into the crank case - bottom left side of the oil pump boss.
I'll Red Loctite the grub screws and breather screws after vapour blasting.

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Barrels bead blasted and rebored + .020".
Yet to decide on rattle can High Temp Black or Powdercoat.

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Re: '71 750 Commando Rebuild

Postby motorson » Mon Aug 08, 2016 9:19 am

I trust red locktite a lot. But, it wouldn't be a bad idea to center punch the sides of your grub screws. Especially because those are never coming out again.
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Re: '71 750 Commando Rebuild

Postby ELMZY » Mon Aug 08, 2016 4:56 pm

motorson wrote:I trust red locktite a lot. But, it wouldn't be a bad idea to center punch the sides of your grub screws. Especially because those are never coming out again.

Yeah, good call motorson.
That reminds me about the crank bolts. :idea:
The top four were punched when I stripped it (bottom two studs had the locking tabs bent over).
Definitely good for peace of mind.
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Re: '71 750 Commando Rebuild

Postby ELMZY » Tue Aug 16, 2016 11:28 pm

Just received my first shipment of quality "bling" from cNw.
They'd have to be the finest motorcycle products I've ever had in hand - and they came with installation instructions.
Expensive gear, but you get what you pay for.
In the past I've ended up going without altogether because of affordability issues and my reluctance to buy poor quality products.
Not this time. It's a once in a lifetime build so I'm "goin' top shelf" - even if it means recycling assets.
Obviously there are plenty of mid priced items out there that are more than adequate for a vintage motorcycle rebuild but, it seems the growing trend of setting up in Asia and bangin' out cheap shit is on the up.
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Re: '71 750 Commando Rebuild

Postby Fast Eddie » Wed Aug 17, 2016 1:07 am

The more you get from Matt... the more impressed you will be...

As you say, you get what you pay for. On top of that, my philosophy is that if you are going to keep a bike for a long time, the extra cost of 'doing it right' is nothing when amortised over those years. Balance that with the enjoyment and pride you will have from having 'done it right' and its a no brainer...

Wives tend not to agree. But wadda they know...?!?
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Re: '71 750 Commando Rebuild

Postby ELMZY » Wed Aug 17, 2016 3:17 am

Fast Eddie wrote: my philosophy is that if you are going to keep a bike for a long time, the extra cost of 'doing it right' is nothing when amortised over those years. Balance that with the enjoyment and pride you will have from having 'done it right' and its a no brainer...

Wives tend not to agree. But wadda they know...?!?


Well said Fast Eddie.

I'll drink ta that.

In fact - I am :wink:
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Re: '71 750 Commando Rebuild

Postby ELMZY » Wed Aug 17, 2016 6:40 pm

Stuffed up the paint job on the barrels.
I used VHT Caliper paint - aerosol.
Their Engine paint has Engine Primer listed but not the Caliper paint - so I didn't use it.
Bad move. I should of known better.
Went to trial fit it with my new cNw / ARP barrel studs and the paint chipped off around the holes.
Scraped the flange with a screwdriver and it came off pretty easily.
As far as the prep goes I was thorough (except for the primer) :
# Scrubbed it in a bucket with HD detergent - hosed off and dried out in the sun.
# Next day hit it with compressed air, brushed it down with prepsol wax and grease remover and wiped dry with a clean rag.
# Masked it up and sprayed with contact cleaner (alcohol) - another clean rag wipe.
# Gave it the once over with a heat gun.
# Weather was sunny, 22 deg C, no wind, low humidity.
# Gave it one light coat followed by two medium coats - looked good.
# Let it dry for 3 hours in the sun, then baked it the oven for 1 hour @ 100 deg C (wifey's in the States) 8)

I definitely advise primer for anyone attempting this with VHT Caliper paint.
I just had a good read of the Barrel Coatings/Heat Dissipation thread by comnoz.
I'm goin' Powder Coat this time - I'll drop it off when I pick up the frame.
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Re: '71 750 Commando Rebuild

Postby gortnipper » Wed Aug 17, 2016 7:30 pm

I used some caliper paint on some small frame pieces I needed to paint, and used primer with them. I was not happy with the results of the finish as it just looked very sloppy despite careful application, and ended up stripping it off. Rustoleum ended up looking great.
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Re: '71 750 Commando Rebuild

Postby ELMZY » Wed Aug 17, 2016 8:05 pm

gortnipper wrote: Rustoleum ended up looking great.

Yeah, came across this guy during my research - good for 650 deg C.
Went for the name brand.
Still, I left out a major ingredient...............PRIMER.
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Re: '71 750 Commando Rebuild

Postby gortnipper » Wed Aug 17, 2016 8:19 pm

mmm....reminds me we have some Angus Scotch fillet cutlets for dinner.
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