Band-aid for a 750

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timson4

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Jan 23, 2015
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Howdy Folks!

There was a discussion not too long ago about squeezing a bit more life from a haggard engine, but I´d like a few suggestions for my situation:

The Skinny: a recently acquired 1970 750 needs some TLC so I can run it until I can re-do the top end. Full rebuild is inevitable, but need to postpone teardown and enjoy bike now. Need advice to nurse it along short-term.

The Good: Engine runs, revs, and idles great, with good power and usual symptoms expected of an old motor: minor oil leaks, wet-sumping, and smoke on startup that clears after warm-up (mostly left cylinder). No odd noises.

The Bad: After I got it home, discovered the gearbox nearly empty and primary totally empty of oil (leaked out or was never oiled???). Clutch was maladjusted.

The Ugly: Oil tank full of sparkly oil. Yes, fine magnetic swarf.

Measures taken:
  • Resisted urge to flog the previous owner(s) for their negligence.
  • Put ATF in gearbox, adjusted clutch.
  • ATF in primary.
  • Drained oil tank and sump; cleaned out tank with brake cleaner and removed metal flakes with magnet
  • Removed Lockheed oil cooler and installed an inline transmission filter instead (will install a proper oil filter/holder soon. Urge to flog PO is great. oil cooler!)
  • Plumbed a Mike's XS reed valve in cam-end crankcase breather line to oil tank (already had one on hand. will consider the JS crossmember-friendly sump reed valve for near future)
Measures planned for this weekend:
  • Open timing side to clean out and refresh oil pump
  • Clean out rocker oil feed lines with suitable spray solvent (WD-40?)
  • Clean out any swarf beneath rocker covers
  • Pour oil around rockers to rinse down pushrods and out sump?
  • finish tune-up, button her up and go!
What else can/should I do to clean up this engine and enjoy the bike until I can open it up and give it the attention it needs? I think the damage is done and we all know that these motors can take a flogging, so I´ve little reason not to. Thanks for your suggestions!

timson
 
Personally, I would take out the ATF and put in the recommend oil, at least in the gearbox. Doing the oil pump might be nice as you will have to anyway when you rebuild, but it must be working - then engine hasn't blown up! Otherwise, it's good to go to Winter IMHO.
 
ATF in the primary is generally considered ok.
I agree with Greg, ATF in the gearbox is too light.
Sparkly bits in the oil tank may not be that big of a deal, depending what you did to discover them. It is possible that the tank has never been thoroughly cleaned. But if all you did was drain the oil and it come out sparkly, that is it a different matter.
Still, if the bike runs all right, you probably aren't going to do much damage by riding it in the meantime.
 
If you have fine magnetic particles in your oil, then you are feeding this into the engine, which means your big end bearings will be embedded with metal, your crank will be wrecked, any other bearing surface fed by the oil, eg top end, will be damaged. The metal particles could be from main bearings disintegrating. If so, your pistons will be embedded with shiny bits and your bores will be damaged. I'd pull it apart. Graham
 
velo54 said:
If you have fine magnetic particles in your oil, then you are feeding this into the engine, which means your big end bearings will be embedded with metal, your crank will be wrecked, any other bearing surface fed by the oil, eg top end, will be damaged. The metal particles could be from main bearings disintegrating. If so, your pistons will be embedded with shiny bits and your bores will be damaged. I'd pull it apart. Graham
Click to expand...
If all that will happen, it already has. He says he will rebuild but wants to ride some first and the bike is running OK. IMHO, ride until winter - winter in most of the US is coming soon.
 
Oil film thickness in the big end is what you need, so good oil pressure tells you the oil is getting there in the right amount and an oil with inherent oil film thickness strength will supply the rest. Fully synthetic oil has the best oil film strength, a 20/60W will work with the worn rings.
 
Many visible magnetic metal flakes would worry me.
It's not the lead in the con rod big end bearings.
It's likely not something under the timing case cover
It's likely not from the head so that leaves moving parts like crank journals, crank end bearings, big ends and piston walls.
Putting a filter in is a good idea, but it won't stop whatever is that has been failing.
If it were mine I would want to play it safe and possible avoid further catastrophic damage so i would not ride it and pull it apart soon.
Dennis
 
I have a 70 model. I use a transmission filter in the oil return line. It's a 50 micron filter with a doughnut shaped magnet to catch ferrous metal particles. On solid lifter push rod engines the cam/cam followers are weak point. The thing that protects them is good oiling and good oil. If your oil pump is worn out, you are just insuring a more complete rebuild in the future by flogging it now. I've seen a friend's commando wear through, and spit off, the stellite pad lamination of one of his followers. The pad pinballed around inside his engine and beat up his connecting rods so they were also not reusable. He didn't notice the problem until one cylinder cut out when he went to pass a car on a B-road and the pad let go in pinball fashion.

Last fall my own bike was making a rhythmic growling noise. I assumed it was a cam lobe growl since cam lobe contact is intermittent. I pulled the head and barrels and found 2 followers starting to pit ever so slightly, so I resurfaced them. I took a chance on the cam being ok, and I rebuilt the oil pump. I thought that maybe the oil pump wasn't oiling well enough and those 2 cam lobes were starting to wear because of diminished oiling. I had no noises or metallic oil contamination this entire riding season so far. I just did an oil change on Sunday and I use a magnetic sump plug which had a normal tiny bit of metallic fuzz on it, and I strained the old oil through 50 micron filters and had zero particles from either the tank or the sump. The oil I removed had no metallic look to it whatsoever. Maybe, I might have gambled and won. (for now)

There are things you can observe to "guess" about how your cam and followers are doing. You can pull the plugs out to roll the engine over and watch the valves go up and down. If one or more of the adjusters have a lot more thread exposed, sometimes that's an indication of follower pad wear or delamination, because if the follower wears and gets shorter the adjuster has to extend to get the valve gap correct.

I suppose your idea that everything is already ruined is probably true. Hopefully you don't seize up your engine and put a connecting rod through the case at high speed. Then the most important part could get broken, the nut behind the wheel.....
 
A Norton 750 will run a surprisingly long time with your described symptoms. Especially if you take it relatively easy. Do as you currently plan to do. Everything wearing down is replaceable. All you need is money, the skill to replace the parts, and a good machinist for any cylinder boring or crank journal sizing or polishing work.
 
A lot are not going to like this but I been mixing STP with my Norton oil since 1982 after I had my first rebuild when converting my motor to the Featherbed frame, in my younger days I flogged the sh it out of my Norton, burn outs and doing stupid things, yes young and silly, wore out my bores from the burn outs, with the rebuild 40 oversize Hepolite pistons with a very tight min final hone between bore and pistons, after the run in was when I started to mix the STP to my motor as well regrinding the lifters when I did the rebore, my stock cam was built up and reground to a 2S cam profile, well to this day I am still running with the same over size bore and the same lifters as well same cam.
I had to replace my crank case as from my canning days had a few hairline cracks around the main oil seal as well one broken part of the front case where the front middle stud went in, I replace the case about 20+ years ago and everything inside my motor was still very good, bores were still tight and no wear on the lifters, bearings were all good even the conrod slipper bearings but I replaced them all when I put the new cases on, to me the STP has done its job of extra protection to my motor, my Norton was an everyday ride for most of its life and has clocked up a lot of miles, its semi retired now since 2013 but I still ride it regularly as my Thruxton has taken over the everyday rider, but I have more fun on my old Norton and it will out see my life.

Ashley
 

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