EEEEEKKK! Airhead Valve/Piston Interference - Page 5

wmax351 · 10-04-2011, 12:51 PM

Quote:

Originally Posted by Max Headroom

Try fitting a pair of standard BMW pushrods. I know of another recently rebuilt engine which had issues with rough idling and loss of power when hot, yet it ran fine when cold. It was also fitted with a set of SJ pushrods, and eventually it was discovered that they were growing when hot and the valve clearance would close up.It wasn't an obvious problem, and kept folk guessing for quite a while.

Between that and a thicker base gasket, most of the issues would be sorted.

I originally had the BMW pushrods. Made the same noise. I checked clearance cold and hot, both were fine.

wirewrkr · 10-04-2011, 12:55 PM

I'm still waiting for someone to compare CROWN HEIGHTs and Valve pocket heights.
C,mon youse guys..............

wmax351 · 10-04-2011, 01:21 PM

Quote:

Originally Posted by wirewrkr

I'm still waiting for someone to compare CROWN HEIGHTs and Valve pocket heights.
C,mon youse guys..............

In regards to compression?

I'll have my dad take some measurements on that. What is the best way to go about that?

robtg · 10-04-2011, 01:26 PM

Valve sticking in the guide and the piston hammering it closed?

anotherguy · 10-04-2011, 01:36 PM

Quote:

Originally Posted by supershaft

Clay? I rather use solder. On a beemer you can measure valve clearance with solder through the spark plug hole. You can put it together for keeps and only have to take it back apart if there is a clearance issue. Plus solder is much easier to get a caliper around and accurately measure down to the thousandths.

Most of us beemer guys would call this issue highly unusual. All original stock BMW parts? No need to measure.

Highly unusual or not measurement would have prevented this. I'm not surprised you would shortcut it. Solder doesn't cover the entire radius of the eyebrow. And cast in eyebrows aren't concentric with the bore axis.

Airhead Wrangler · 10-04-2011, 01:43 PM

Quote:

Originally Posted by wmax351

In regards to compression?

I'll have my dad take some measurements on that. What is the best way to go about that?

Measure the top of the wristpin hole to the top of the piston with a caliper. Also measure the installed valve spring length also.

bmweuro · 10-04-2011, 01:56 PM

Visually it looks like the piston is stick up to high in the cylinder. My guess would be the cylinder has been machined down at the base.

wirewrkr · 10-04-2011, 02:19 PM

Quote:

Originally Posted by robtg

Valve sticking in the guide and the piston hammering it closed?

Oooooh, Bobby, I think that makes alot of sense if both guides were not sized correctly.

anotherguy · 10-04-2011, 02:20 PM

When a stuck valve is struck by the piston it bends and gets much worse from there.

supershaft · 10-04-2011, 04:46 PM

Quote:

Originally Posted by anotherguy

When a stuck valve is struck by the piston it bends and gets much worse from there.

Well, at least you are cut and dry with everybody.

Shortcut it? I am starting to wonder WHO is the short cut?

Mouth people under the bus elsewhere.

JonnyCash · 10-04-2011, 05:06 PM

Quote:

Originally Posted by robtg

Valve sticking in the guide and the piston hammering it closed?

I had this happen on a SABB marine diesel. The valve train was not engineered to rotate the valves, and the stems would get carboned up and would make the valves stick very slightly open. Being that this engine was rebuilt 100 miles ago, I'm sure it's not a carbon buildup issue, but theres a lot of other ways a valve could stick. Unfortunately, now that things have beaten on each other, if on inspection you find that a valve is sticking, you won't know which came first, the chicken or the egg.

anotherguy · 10-04-2011, 05:21 PM

Quote:

Originally Posted by supershaft

Well, at least you are cut and dry with everybody.

Shortcut it? I am starting to wonder WHO is the short cut?

Mouth people under the bus elsewhere.

You're a hack and a charlatan. If he'd have checked at assembly we wouldn't be having this conversation.

Beemerguru · 10-04-2011, 07:11 PM

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.

wmax351 · 10-04-2011, 07:47 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.

I can measure it for sure this weekend. I'll post up the results.

supershaft · 10-04-2011, 08:10 PM

I do go so far as turning the engine over enough times to get through all the valve cycles for each cylinder and make sure nothing is hitting. I have never had anything hit so far. It is a lot easier than measuring your valve clearance with clay. ESPECIALLY when you have the cams off a DOHC engine to adjust some shims. The idea that you should disassemble your engine, reassemble it with clay in it, take it back apart again to measure the valve clearance the clay witnessed, and then reassemble it again. How do you check the last assembly??

(You could do it with solder like I suggest!) Doing that every time you can get into any trouble isn't really realistic. Not even close.

10-04-2011, 12:55 PM	#62
wirewrkr the thread-killer Joined: May 2008 Location: HIGH desert Oddometer: 4,297	I'm still waiting for someone to compare CROWN HEIGHTs and Valve pocket heights. C,mon youse guys.............. __________________ www.wirewerkes.com KILL YOUR TELEVISION !!!!

10-04-2011, 01:56 PM	#67
bmweuro Mad Scientist Joined: Nov 2003 Location: Chico, California Oddometer: 2,964	Visually it looks like the piston is stick up to high in the cylinder. My guess would be the cylinder has been machined down at the base. __________________ BOXER Metal BMW Biker Scum BMW Mad Scientist! VBMWMO #7770, BMW MOA #48694 & Airhead BMW Club #600

10-04-2011, 02:20 PM	#69
anotherguy Beastly Adventurer Joined: Jun 2009 Location: in the foothills now.... Oddometer: 4,315	When a stuck valve is struck by the piston it bends and gets much worse from there. __________________ When injustice becomes law,resistance becomes duty. Thomas Jefferson

10-04-2011, 07:11 PM	#73
Beemerguru Beemerguru...G/S guy Joined: Nov 2006 Location: Foster City, CA Oddometer: 635	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. __________________ Greg Hutchinson BMW Club of Northern California, Ambassador, BMW MOA, Vice President Vintage BMW Club http://gregsgssite.shutterfly.com/

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10-04-2011, 01:26 PM	#64
robtg Gnarly Adventurer Joined: Jun 2007 Location: san jose Oddometer: 359	Valve sticking in the guide and the piston hammering it closed?

10-04-2011, 08:10 PM	#75
supershaft because I can Joined: Sep 2010 Location: San Francisco Bay area Oddometer: 6,070	I do go so far as turning the engine over enough times to get through all the valve cycles for each cylinder and make sure nothing is hitting. I have never had anything hit so far. It is a lot easier than measuring your valve clearance with clay. ESPECIALLY when you have the cams off a DOHC engine to adjust some shims. The idea that you should disassemble your engine, reassemble it with clay in it, take it back apart again to measure the valve clearance the clay witnessed, and then reassemble it again. How do you check the last assembly?? (You could do it with solder like I suggest!) Doing that every time you can get into any trouble isn't really realistic. Not even close.