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Old 07-06-2014, 08:25 AM   #1
hangman OP
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Valve/ head/ cylinder evaluation

Hi, I'm a rookie and I took the heads off my 1982 R100 today.
I had to check/ replace the rocker needle bearings because I had some strange valve clearances (opening up/ excessive closing), and a bit "too noisy valves". Since I haven't had much time to ride since I got this bike, I felt it would be best to have a look at the valves and seat recession.

The PO claimed that the 21000km/ 13000 miles on the clock was correct, but I don't know what to believe.

How do you folks think this looks? Should I take the valves out too? (don't have tools for this).

And while the heads are off, I might not get the cylinder base to seal without resealing(?), and then maybe I should take off the barrels and check some more things? I have the Motobins top end gasket & seal set.

IMG_4761 right head inside face

IMG_4763 right head exhaust valve from side

IMG_4770 right piston face

IMG_4775 right barrel bore towards front

hangman screwed with this post 07-06-2014 at 08:31 AM
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Old 07-06-2014, 09:20 AM   #2
disston
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The intake valve in the pic of the head looks recessed. I actually think this is a trick of the shading, is it? It would be the opposite of norm because the exhaust is usually the one that has problems the earliest.
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Old 07-06-2014, 09:55 AM   #3
100RT
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You didnt need to remove the heads to replace the bearings. So, you probably need the cylinder base o-rings (3) and push rod tube rubbers plus a new head gasket to get it to seal up.

13k should be trouble free on your question. There is a learning curve to airheads but sometimes its best to ask before you jump. Lots of help is available.
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Old 07-06-2014, 10:12 AM   #4
Bill Harris
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Can't tell with the valves assembled. Especially if you are a rookie and don't have the tools, etc, you need to get the heads down to a trustworthy machine shop for evaluation and, if need be, repair.

How did the rocker needle bearings look?

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Old 07-06-2014, 10:17 AM   #5
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The evaluation should have started before you took the engine apart with a leak down test. Not so much for the numbers but for where it's leaking at. A lot of blow by? Do a compression test too. Real bad leak down numbers and decent compression test numbers usually mean lined up ring gaps. Do not install your pistons with the ring gaps lined up per Duane Ausherman. I have had to take engines back apart for people doing that. The rings don't 'spin' nearly as much as some claim. I know for helping with race bikes and having the engines apart a lot.

Pour 'hot' solvent into the ports and hold the heads above yours for a minute or two. If solvent doesn't weep past any valves, chances are you are good to go.

Check the lifters for flaking.

Make sure the stud O-rings don't fall onto the studs just before the cylinders are pulled against the case.

Use Durko spread very thinly on the cylinder base.

Clean the mold release off the inside and outside of the pushrod tubes and install them dry.

Don't wait 600 miles to re-torque heads. Do it after two heat cycles and again at 600 miles. Don't loosen the head nuts to check torque.

Space ring gaps per BMW.

Visually check top of top ring groove for wear.

If the rocker arm bearings look OK, slowly rotate them on their shafts and feel for notched bearings. Replace if notched.

I would not take your heads to a 'trustworthy' machine shop unless they are known trustworthy with BMW airhead heads and even then I would look into the situation much more than that.

supershaft screwed with this post 07-06-2014 at 10:31 AM
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Old 07-06-2014, 02:42 PM   #6
hangman OP
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Thanks for the input.

I realize I should have started out with a compression test. Will do that next time :)

Well, I borrowed a valve spring compression tool and got the valves out. I have only done the right head so far, as I was pretty sure it had a bad bearing.

Status:
- Rocker bearings are visibly intact and there is no feelable wear on the shafts. I think there is a tiny bit radial play, but probably not more than it has to be.
- Valves. As far as my understanding goes, they are reusable. There is some pitting on the exhaust valve contact area, and a few pits on the seat. I think I should clean the carbon and lap them with valve grinding compound. Valve stem is pretty even along the wear part.
- Guides. There is a wee bit of play on the exhaust guide. Maybe there should be some room for heat expansion?

I am tempted to try and reuse the gasket and seals. Stupid?

I'm starting to believe that the 21000km/ 13000 miles on the odometer might be correct.

Have a look at these new pictures, and tell me what you think:





















And for those interested, this is what the rest of the bike looks like :)

hangman screwed with this post 07-06-2014 at 02:52 PM
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Old 07-06-2014, 03:24 PM   #7
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Hei, hangman,

noisy valves is usually not a sign of airhead problems, rather the other way around. From the honing pattern visible in your cylinder bore, it certainly doesn't look like that cylinder has done an extremely high mileage.

If no excessive wear can be measured, I'd put everything back and just run the bike, whilst monitoring the valve clearance regularly. You mentioned "a wee bit of play" of the exhaust valve/guide - how much is "a wee bit"? Cfr. e.g. http://www.largiader.com/articles/valves/

Apart from valve guides, a worn timing chain can result in a wobbly valve operation and uneven idling, but you don't mention if the idling is erratic. Based on the claimed mileage and cylinder bore, I wouldn't suspect this to be a problem.

Re reusing gaskets: valve cover gaskets can last a long time. Although the cylinder head gaskets don't have to separate coolant and oil, the top cylinder studs supply oil to the rocker shafts, and the pushrod tubes returns oil to the sump. If the seal surface around those holes in the head gaskets are broken, oil leaks can result.

Nice looking bike!

PS
Hvor i Norge holder du til?
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Old 07-06-2014, 04:58 PM   #8
disston
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This is a low mileage engine. I hope you don't cause more damage than needed by all this disassembly. We normally try to not fix stuff that isn't broken or shows problems.

If you are going to lap the valves in make sure you use the water soluble lapping compound. The oil soluble one is hard to wash off and ends up in the engine oil.

Be careful to wash all of the valve grinding compound off and don't get any in the valve guides.

Do a lite valve lapping.

Use new gaskets, O-rings and pushrod seals to put it back together. Make sure you use a torque wrench, please. The cylinder head bolts should be torqued to 25 ft/lbs. But no higher than 26 ft/lbs.
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Old 07-06-2014, 06:05 PM   #9
AntonLargiader
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I'd believe it's a low mile bike. The valves are exactly what I typically see new valves at: 7.945mm. Recession? No idea where that came from; I can't see any real seat wear at all. However, I do see in the second picture of the valve seats something that I can't really see well enough: what looks like an irregularity in the intake seat near the spark plug. Might just be the light. Anyway, if a seat doesn't make even contact all the way around, it needs to be touched up with a cutter or stone. Lapping is not enough.
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Old 07-07-2014, 12:47 AM   #10
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Quote:
Originally Posted by disston View Post
. We normally try to not fix stuff that isn't broken or shows problems.
.
Since when?

What else would we do with all that spare time?


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Old 07-07-2014, 04:28 AM   #11
therealbatman
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Quote:
Originally Posted by Padmei View Post
Since when?

What else would we do with all that spare time?


UMMMMM......Ride?
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Old 07-07-2014, 07:28 AM   #12
AntonLargiader
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The year of the bike didn't fully register with me at first. You should completely clean the inside rim of the exhaust seat, and see how many grooves are there. The updated seats (which your bike would not have had from the factory) will have two grooves very close together, while the original 'lead-free' seats have one groove. If you have one groove, you have the seats that will likely suffer recession in the future. Not always, and usually not at low mileage, so it isn't something you need to do now if you don't want to, but if you are planning to put 100,000 km on the bike in the next few years you probably should.
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Old 07-07-2014, 08:58 AM   #13
Bill Harris
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Quote:
The updated seats... will have two grooves very close together, while the original 'lead-free' seats have one groove...
Ah, that is what was nagging at me about this problem, and the attached photos.

Thanks!

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Old 07-07-2014, 03:52 PM   #14
hangman OP
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It's great to have so many knowledgeable people hand-holding me!

tsADV:
I tried to measure the guide/ stem play, and I think I get a movement of about 0.4mm with the valve just above the seat. I'd say it's 1/3 of the movement of Anton's mouse-over image. The intake play is a little less.
The idling is not perfectly even, but close.
Jeg holder til ved Hamar. Ikke noe stort airhead-miljø her :)

disston:
"We normally try to not fix stuff that isn't broken or shows problems." - I just HAD to see the inside for the peace of mind!

AntonLargiader:
The "irregularity" in the intake seat could have been the light or some debris. It's good. I took a couple of new pictures of the exhaust guides. They show small dents on the seat taper. Could this be from trapped carbon particles? Anything to worry about?
I tried to clean the inside rim with a knife and a steel brush to look for grooves. Is there one, or none?

I do need some advice for the cleaning. Do I have to make things shiny? Is a steel brush on a Dremel OK? How do I clean the areas next to the contact areas of the valves and seats, and the lower end of the stems?

IMG_4807 right head exhaust valve seat 4

IMG_4810 right head exhaust valve seat 6
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Old 07-07-2014, 05:32 PM   #15
AntonLargiader
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I don't see a groove there.

EDIT: Your excellent pic shows a lot of small dents in the seat. They need to be ground to a fresh surface. Possibly they have been replaced with non-BMW seats, which is probably fine. Or else the unleaded 'improved' seats weren't used in Europe. I don't know.

Here's a 1985 head with the revised seats. You can clearly see the two grooves on the exhaust.

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