EEEEEKKK! Airhead Valve/Piston Interference - Page 6

kbasa · 10-04-2011, 08:26 PM

Quote:

Originally Posted by Beemerguru

I know it's always the right thing to do,,,measure for head interference when assembling a new engine...but in reality,,,all stock BMW parts,,rotates with no interference on assembly, has the proper valve clearance, etc, I would think everyone on this list would think the engine was good to fire up,

Of course when that first loud WHACK, WHACK comes out...I don't think I'd see if it would go away in a 100 miles. That head would be off in 15 minutes.

Measure the piston and measure the cylinder...this crowd has been in suspense for too long. Post the findings..everyone will grab their favorite manual and tell you if the problem lies in either part.

Valve seats are cut to correct depth and valve face is correct diameter at that point?

wmax351 · 10-04-2011, 10:57 PM

Here's more pics of the heads, cylinders, and pistons. Measurements will happen this weekend.

https://skydrive.live.com/redir.aspx...FB71801A7E!766

tokyoklahoma · 10-04-2011, 11:35 PM

I would bet that, at some point the mating surface of the case (where the jugs bolt up) has been flycut to clean-up the surface. Thus making the assembled height too short without a thicker gasket, or double gasket, or gasket and shim.

Padmei · 10-05-2011, 12:15 AM

What should the normal distance be from the piston crown to the head at TDC?

pommie john · 10-05-2011, 12:56 AM

Quote:

Originally Posted by Padmei

What should the normal distance be from the piston crown to the head at TDC?

I don't know the official figures, but on a race engine 35-40 thou minimum. On a road bike I'd guess about 50 thou .
You need about the same piston to valve clearance too.

bmwhacker · 10-06-2011, 06:12 PM

wmax351 · 10-09-2011, 12:19 PM

Talked with the local Motorcycle shop (Bill at Quality Motorcycles). Going to have him inspect the heads and pistons, and see what needs replaced.

We were discussing the cause, and most logically, it seems like somewhere in the last 40 years, something was machined down, either heads, cylinders, or cylinder pads. I'm going to repair the damage, and then put the low test gasket (1.2 mm) on, button it up, and clay the motor. Should fix the problem.

Bill Harris · 10-09-2011, 03:29 PM

You might want to measure some volumes and calculate the compression ratio of this particular collection of engine components. It won't run happily on available fuel with a 15:1 CR...

wmax351 · 10-09-2011, 03:43 PM

Quote:

Originally Posted by Bill Harris

You might want to measure some volumes and calculate the compression ratio of this particular collection of engine components. It won't run happily on available fuel with a 15:1 CR...

Probably would be the wise thing to do. These are all stock, so as long as there is clearance, it should be fine. Can't hurt to check though.

datchew · 10-09-2011, 04:50 PM

this is one of the best threads I've seen in awhile.
Every time I get cocky about what (I think) I know, I run into threads like this and regain humility.

Some of the questions you guys (and girls?) are asking demonstrate a tremendous depth of understanding of how these bits of ironmongery work.

What an amazing braintrust.

... now don't get a swelled head.

wmax351 · 10-09-2011, 05:41 PM

Quote:

Originally Posted by datchew

this is one of the best threads I've seen in awhile.
Every time I get cocky about what (I think) I know, I run into threads like this and regain humility.

Some of the questions you guys (and girls?) are asking demonstrate a tremendous depth of understanding of how these bits of ironmongery work.

What an amazing braintrust.

... now don't get a swelled head.

Also a good example of the combined knowledge of the internet. You combine all the gurus', as well as the tinkerers' knowledge, and you could fill volumes. Each person adds their little (or large) contribution, and you get something amazing. I'd like to see an airheads wiki.

DoktorT · 10-09-2011, 07:58 PM

Quote:

Originally Posted by wmax351

I'd like to see an airheads wiki.

Now I know I have seen something like that somewheres. Maybe IBMWR or something like that.

Here is one down for service.
http://wiki.airheads.org/index.php?title=Main_Page

The there is wikipedia itself

http://en.wikipedia.org/w/index.php?...ofile=advanced

wmax351 · 10-20-2011, 03:48 PM

Well, here's an update. Took the heads to the local motorcycle repair guy, who does a lot of work on airheads. He checked them out, and says they seem fine. We're going to have him look at the pistons too, but he thinks they should be run-able. We're assuming that at some point, something has been machined down. Rather than figure out what it is, we are just going to fix the problem. We'll start with the low test, 1.2 mm base gaskets, check for piston crown clearance with clay, then measure tdc volume with mineral spirits, and adjust each side to be equal with .5mm high test base gaskets.

Bill Harris · 10-20-2011, 06:28 PM

Sounds like a plan... :)

wirewrkr · 10-20-2011, 08:35 PM

Early (70-75) jugs I'm measuring this: see picture
76 and later are running around 118mm even or thereabouts.
I compared several original jugs. I have many several.

10-04-2011, 11:35 PM	#78
tokyoklahoma Studly Adventurer Joined: Jun 2011 Location: N.W. Arkansas Oddometer: 754	Machined Case I would bet that, at some point the mating surface of the case (where the jugs bolt up) has been flycut to clean-up the surface. Thus making the assembled height too short without a thicker gasket, or double gasket, or gasket and shim.

10-06-2011, 06:12 PM	#81
bmwhacker Still on 3 wheels Joined: May 2009 Location: MONTANA NATIVE from NATIVE MONTANA Oddometer: 3,367	__________________ http://jupiterhack.blogspot.com Living proof you shouldn't play with matches

10-09-2011, 03:29 PM	#83
Bill Harris Confirmed Curmudgeon Joined: Sep 2008 Location: backwoods Alabama Oddometer: 3,850	You might want to measure some volumes and calculate the compression ratio of this particular collection of engine components. It won't run happily on available fuel with a 15:1 CR... __________________ '73 R60/5 Toaster

10-09-2011, 04:50 PM	#85
datchew Don't buy from Brad Joined: Aug 2005 Location: Savannah - the dirty south Oddometer: 7,403	this is one of the best threads I've seen in awhile. Every time I get cocky about what (I think) I know, I run into threads like this and regain humility. Some of the questions you guys (and girls?) are asking demonstrate a tremendous depth of understanding of how these bits of ironmongery work. What an amazing braintrust. ... now don't get a swelled head. __________________ On tap:Nada Aging: 3 experiments in mead - blackberry, apple, and straight honey

10-20-2011, 06:28 PM	#89
Bill Harris Confirmed Curmudgeon Joined: Sep 2008 Location: backwoods Alabama Oddometer: 3,850	Sounds like a plan... :) __________________ '73 R60/5 Toaster

10-04-2011, 10:57 PM	#77
wmax351 ^OP Studly Adventurer Joined: Mar 2011 Location: Marin County and Berkeley, CA Oddometer: 740	Here's more pics of the heads, cylinders, and pistons. Measurements will happen this weekend. https://skydrive.live.com/redir.aspx...FB71801A7E!766

10-05-2011, 12:15 AM	#79
Padmei enamoured Joined: Mar 2008 Location: Nelson New Zealand Oddometer: 2,481	What should the normal distance be from the piston crown to the head at TDC?

10-09-2011, 12:19 PM	#82
wmax351 ^OP Studly Adventurer Joined: Mar 2011 Location: Marin County and Berkeley, CA Oddometer: 740	Talked with the local Motorcycle shop (Bill at Quality Motorcycles). Going to have him inspect the heads and pistons, and see what needs replaced. We were discussing the cause, and most logically, it seems like somewhere in the last 40 years, something was machined down, either heads, cylinders, or cylinder pads. I'm going to repair the damage, and then put the low test gasket (1.2 mm) on, button it up, and clay the motor. Should fix the problem.

10-20-2011, 03:48 PM	#88
wmax351 ^OP Studly Adventurer Joined: Mar 2011 Location: Marin County and Berkeley, CA Oddometer: 740	Well, here's an update. Took the heads to the local motorcycle repair guy, who does a lot of work on airheads. He checked them out, and says they seem fine. We're going to have him look at the pistons too, but he thinks they should be run-able. We're assuming that at some point, something has been machined down. Rather than figure out what it is, we are just going to fix the problem. We'll start with the low test, 1.2 mm base gaskets, check for piston crown clearance with clay, then measure tdc volume with mineral spirits, and adjust each side to be equal with .5mm high test base gaskets.

10-20-2011, 08:35 PM	#90
wirewrkr the thread-killer Joined: May 2008 Location: HIGH desert Oddometer: 4,297	Early (70-75) jugs I'm measuring this: see picture 76 and later are running around 118mm even or thereabouts. I compared several original jugs. I have many several. Attached Images __________________ www.wirewerkes.com KILL YOUR TELEVISION !!!! wirewrkr screwed with this post 10-21-2011 at 07:03 AM

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