Get ahead.

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Hi all,

I had a great day :D Spent 5 hours and managed to get the head off my 850 MKIII without damaging any gasket surfaces, breaking off any studs, or rounding any nuts :shock: took me a while to find the two upside down puppies, but I did. And what's with the pushrod juggling act :lol:

Anyway, from my limited experience, everyhting looks OK except a worn groove in the top of one exhaust valve stem. The other three have a polished look.

Not too much carbon, so I'll remove it with a brass wheel on my dremel.

What else should I look for? Is it advised to have the head rebuilt? The valves look OK from the top, but I can't see the seats from where I'm sitting :lol:

All advice welcome.
If the worn spot is where the adjuster runs it was probebly run with the valves out of adjustment or as little softer valve. that needs to be corected. while the head is off I would look at the guide's for sure, probebly worn bad if it has over 10,000 miles on it also put new intake seals on it. the two frount studs on the head need to be sealed if they are drilled through along with the two small studs in the cylinder. think about new head bolts for reassembly.

I'd do a complete rebuild on the head, especially since you haven't run the motor. You don't want to put it all back together and find out that the guides are leaking or a valve is bent or whatever. while you're at it lift the cyclinder and check out the cam and followers. Mk III's came thru with some soft cams and you may need to replace it. Mine had a bad lobe which of course screwed up the follower too. My head also had a casting flaw that rubbed on one of the push rods. If the cam is chewed up you might as well do a complete rebuild since you will need to split the cases to replace the cam.
Good luck.
Thanks Bill & scooter62!

I gave the head a bath and inspected. All looks OK, but I will take your advice and rebuild -- I have 12k miles. I'll replace the guides and seals as suggested, face off the valve stems, and hand-lap the valve seats (assuming they're OK).

I cleaned out the domes (fun times) and the piston tops. Nothing to worry about -- except that I couldn't clean what looked like a very tough deposit on the valve face underneath a layer of carbon ... almost like metal droplets had been "sputtered" over the valve face and had formed a thin layer. I wonder if someone melted a plug electrode. I will think on what to do with this. There's also a rather large buildup of carbon and crud all inside the exhaust ports. Time for some more dremeling -- maybe a nice port and polish while I'm in there :wink: (just kidding). Wish I had a flow bench.

I also drained the oil from all the places. I found what looked to be a crunched and folded washer in the large drain plug/screen on the bottom. Hmmm. Also looks like the screens have never been touched. The oil was dark, but the sludge in the trap was the consistency of molasses. Nothing a little Gumout and an ultrasonic cleaner couldn't handle :) No metal on the magnet :) Oil filter looked normal --- I'm guessing 4-5k in service by the looks of things.

Time to pull the cylinders up and check out the other goodies (please be OK, please be OK).

I also took the opportunity to paint my first part. I polished and painted the oil filler cap gloss black :lol: :lol:
one quick word, if you replace the guide's you will have to have the seats ground they will be to far off to lap.

Get ahead

I would not change valve guides just yet unless you see damage to them. Just take out the valves, clean them, use your dremel to clean the exhast ports out, and run a 5/16 reamer trough the guides to remove any carbon that may have entered. Lap the valves and assemble the top end. Be careful you can bend the valves springs with the valve spring compressor. The melted metal you found may have been part of the orginal carburetters. Get used to tearing it apart and assembling it, this will increase your confidence in your bike, your skill and your confidencein your skill. LOL
Thanks sway,

I was debating about doing it or finding someone else, but now that you mention it, I think I trust myself better 8) -- and if I mess up, you guys are here :lol:

I was able to remove the metal deposits with persistent and carefull use of a dremel stainless wire wheel -- took about an hour. Looks good ... but now I'm wondering what's on the flip side -- so into the oven she goes. The spousal unit should appreciate that :lol:

Question: is there a tolerance spec for valve play in the guide?
Get Ahead (Valve specs.)

Valve stems Dia. 0.311 +/- 0.0005
Valve guide I.D. 0.314 +/- 0.0005
That works out to a clearence of 0.003 +/-0.001
guide clearances

I have felt the factory guide clearance specs are a joke. The grossly large clearances were for ease of assembly in a factory environment. Simple, sloppy guides allow the valve to center on the seat easily.
As Bill said new guides will require grinding the seats to realign the seat to the new location of the valve. If I could run a 5/16 reamer through a valve guide of mine, the head would come apart for a rebuild since it would be (to me) fully worn out.
I think I end up with about .0008" on the intakes and .0012 on the exhaust. The thing is you can't really measure the guides accurately since straightness is not accounted for in a "spot" measurement.
I found profe$$ional shops lacking in the level of care I looked for, so I invested a good part of $3k in valve working equipment. After MANY air cooled and water cooled engine valve jobs and 15 years of experience, I finally am an accomplished amature, and am happy to stay that way.

Caution on sloppy guides.....
I am now helping a local club member do a valve job on another (new/replacement) 850 head, since a local shop in leominster, ma (now closed) "exchanged" heads without his knowledge and gave the guy a junk/cracked head. This "new/replacement" 75 head has a bent valve.
Extremely sloppy guides will oil burn and coke up the valve stems and when the valves stick...they will hit the piston or each other and bend. They may not even appear to smoke excessively. Don't let this happen to you. I've seen this more than once....

Being able to remove a valve from a head, and lapping in a valve is a LONG way from doing a valve job. If you find this enjoyable fine, do it. Without the tools ($$$) I think you will be not be able to do quality work. Then as you say, you will be back on this or another board for "help".

good luck :)
5+ commando
2 atlas
3 BSA A-10
3 ducati
1 Dunstall atlas
1 T100R
2 lotus
Dodge diesel
Get ahead

Actually I don't believe every thing I read in a manual, even a Norton shop manual but when I read the same thing in a Vincent shop manual, a Triumph shop manual, a Honda shop manual I think the information might be worth thinking about. I think without good information good work is impossible.

OK you guys :!:

You've succeeded in scaring me :shock: so I'm not going to pull my head apart at this time (my hair out maybe).

I've been calling and driving around. There's a guy near me who only works on Brits, but he's crotchety and pricey (I think). He wants $600 to do a complete valve job (if the seats need to be re-done). This includes St-st valves and bronze guides :cry:

He wants half that if the seats don't need to be re-cut :(

Pass (for now). I don't want him to touch my stuff anyway ... just a feeling. I would prefer to send my parts to the other ocean than go the 2 miles to his shop.

BTW, what is the going rate :?: (and I don't mind sending it to Taxachusetts ... actually, I'm going East in Jan or Feb, so maybe I'll take it as carry-on :lol: :lol: airport security should have a field day).

Anyway, with my limited funds, my plan is now:
Put it all back together after a thorough bath and scrub, as well as a nice cleaning of the combustion area and valve surfaces. I measured the cylinders using the ring method (don't have a mic handy), and there's virtually no ring gap anywhere maybe a 2-3 thou. on one side (but consistent), so I figure I'm OK. I'll mic. the pistons as soon as I dig up the spec.

The guy near me says I should hone or the rings won't seat. Humbug I say :roll:

If it runs fine, I'll just wait until it doesn't. If it doesn't, then I'll get a job :shock: and figure out plan-B.
the guy that does my head work charged me $125 labour to replace the guides, grind the seats, and face the valves. new black diamond valves was $25 each and guides was less than $50 for a set. I would NOT put that head back on as is with out at least checking the guides and replacing the valve seals!!!!!

Surely a good ifdea to replace the valve springs whilst you're at it?
valve guides & piston bore

Information to be gotten.
Did you get this information upon initial inspection/teardown.
1. Was there oil on the OUTSIDE of the guide.
2. Was there oil on the stem of the valve. intake & exhaust.

piston & rings
I reused the rings on both my motors, 750 combat and 75 E-start.
With a snap-on leakdown gauge- leak down 7&9% on the 750, and 2&3% on the my 850 which is the tightest motor I have ever tested.....I did only a light deglaze but am not convinced that in a round, untapered bore it is all that necessary.

Springs-I now have a tester to measure the spring# rate. I am in testing to determine these values, as installed, and at full open, for stock and combat cam, for New and used springs

What is REDO the seat? Change the seats? Original norton seat have a very good alloy and work fine with no lead if the valves are of a good alloy. If the seats are changed and ALL materials supplied, than $600 is high, but not outragous. But I have only changed seats on ONE commando head, one worked on (ruined) by a profe$$ional shop. After many valve jobs/guide changes, you would eventually need to change the seats (maybe 75/100k+ miles). This is quite dependent on how lucky you are after each valve job/guide change.
I've done several Lotus TC heads. At full shop rate would be over $2K.
Hi dynodave et al,

Answer to your post: On inspection -- I don't recall any oil anywhere around/on the guides. There was a light oil layer on the stem ends -- but I expect that. I did my head cleaning and then it went to the parts washer.

I don't have a leak-down tester (nor do I want to shell out for a Snap-On one). I don't mind making a home-made one. Maybe I'll surf and find one.

From the combustion chamber the valve/seat contact area looks real solid with no signs of anything other than smooth clean metal. It's also pretty light-tight (whatever that proves). I just filled the dome with mystery oil to see if any leaks by.

I think the guy near me was hungry for work. My seat looks just fine :shock: :shock:

If I had the cashola, I would do the entire head -- just because. But I'm on a shoestring for now, so the attitude is the absolute minimal purchases I need to get it running without causing damage. My time is free and abundant.
Leak test -- SWAG

I left the Marvel Mystery Oil in the upside-down head over night.

This morning there was some seepage through both the right intake and exhaust valve seats :( It had run down the guides, out the ports, down the studs, and made a 1/2" diameter pool on the bench. The amount left in the head didn't appear to have changed.

I'm guessing maybe 2-4cc or so seeped out. Drat :!:

The left side guides were completely dry.

Back in holding pattern.
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