How to install valve guides?

[Jon K]

I know most people just drop the head off the machine shop - my buddy has a shop (high precision tooling machining for rubber valving) with more than adequate workers and tools to get it done, but I have never actually asked/found out how to install valve guides. Does anyone know what has to be done?

[George M]

Well...the valve guides versus the valve seals is a big difference as you likely know. I know for fact that some that have tried to change the guides have struggled. As I recall this is one of the reasons Bill R posted a long time ago that BMW sells oversize valve (stems). What this promotes is...no need to replace the guides which are a bit risky to change...insertion, retention, perpendicular in 2 planes etc...simply ream the worn guide to the larger size and replace the valve. This approach makes the most sense. I would mic everything before even remotely considering to change guides or valves as these engines can and will do big miles without touching the guides...my personal experience. Valve seal wear however is typical and common and I suggest you take the head apart and mic everything to deduce wear and invariably replace the seals as standard head rebuild practice.
HTH,
George

[Jon K]

Well...the valve guides versus the valve seals is a big difference as you likely know. I know for fact that some that have tried to change the guides have struggled. As I recall this is one of the reasons Bill R posted a long time ago that BMW sells oversize valve (stems). What this promotes is...no need to replace the guides which are a bit risky to change...insertion, retention, perpendicular in 2 planes etc...simply ream the worn guide to the larger size and replace the valve. This approach makes the most sense. I would mic everything before even remotely considering to change guides or valves as these engines can and will do big miles without touching the guides...my personal experience. Valve seal wear however is typical and common and I suggest you take the head apart and mic everything to deduce wear and invariably replace the seals as standard head rebuild practice.
HTH,
George

Thanks George,

I should have given some background. My current M50 non vanos motor at 190k displays (and always had, since about 145k) smoke from the exhaust (blue) when deceling and getting back on the gas. That is symptomatic of valve seals, yes. But, I am building a 2nd M50 non vanos motor without knowing how it previously ran - its BJL4776's motor and ran fine, but I don't know how the guides or seals are. I am replacing the valve seals regardless - debating on the guides.

[George M]

Thanks George,

I should have given some background. My current M50 non vanos motor at 190k displays (and always had, since about 145k) smoke from the exhaust (blue) when deceling and getting back on the gas. That is symptomatic of valve seals, yes. But, I am building a 2nd M50 non vanos motor without knowing how it previously ran - its BJL4776's motor and ran fine, but I don't know how the guides or seals are. I am replacing the valve seals regardless - debating on the guides.
Listen to the advice of Bill and Winfred foremost but there should be no chance to whether they should be changed. Those guys may give a homespun test...like grabbing the valve head with the valve up on the cam lobe...and rocking it...too much play and the guides need to be reworked...but the best way is to pull the valves and mic the guides and stems. There are specs for all that stuff Jon. Over a certain level of wear, then you either ream or replace the guides...no guesswork...cut and dry.
George

[Jon K]

Thing is, I have a non vanos head which uses 7mm valve stems. There is no over sized ID guide available or anything. Replacing valves in a 24v head is a bitch on the wallet. I am thinking of putting in new valve seals and calling it a day. Cleaning the head up and block up and doing my MLS gasket. If the bitch smokes, I will rebuild the head I have from my other engine in full.

Waiting for Bill and Winfred to chime in before I make any decisions.

[Dave M]

Jon, you may already have this, but here goes. As George has already stated, its not a simple task (especially on the 24V), so be sure you need to do it. On the same note, the 'smoke' you are blowing while decelerating under vacuum (assuming clutch is engaged) could also be attributable to worn or broken piston ring(s). I had the same symptoms on my M50 prior to the rebuild. Did you do the simple wet/dry compression test to help determine whether any sinngle cylinder is weaker and whether it might be top or bottom related?

http://img.photobucket.com/albums/v11/dave_macisaac/valve_test.jpg
http://img.photobucket.com/albums/v11/dave_macisaac/valve_test_2.jpg

Good luck with it and let us know how it goes.

Dave

[George M]

Jon,
Dave just posted the spec basis for what I mentioned about putting the valve(s) on top of the lobe and rocking them. Take note that the illustration shows the valve being tested in an extended state. The table shows valve guide wear with a new valve in place but you can perform the same test with the old valve....it simply becomes part of the equation. BTW...it looks as though oversize valves are indeed available of all motors...7.1, 7.2mm stems etc. 0.5-0.8 mm's is actually a fair amount of valve head wiggle. You should be able to deduce this quite simply without even pulling your cam or old valves out....though side to side play will be less with the valve in place yet up on the cam. Check a few of them and see where you stand. Don't absolutely need a dial indicator either...can clamp a block of steel to the head with the valve pulled to one side then measure the gap with calipers by pulling on the valve head in the other direction. Why I mentioned Bill and Winfred is they likely can grab a valve with their hands, wiggle them and tell seat of the pants whether the guides need to be touched. Of course you want to err on the side of conservatism to do the guides...me too.
You should be able to figure out what you need pretty easily and decide just how perfect to make the head. Bill or Winfred may know by experience for example that 1mm of valve head play is acceptable and no foul to oil consumption provided the seals are replaced.
George

[Jon K]

Thanks a lot guys. I agree with both of you that they are a bitch to deal with. How does one actually install the guide though? Do I need to get them pulled and pressed in? I don't want to do them unless necessary - my oil burn could be valve seals as they are most likely the culprit. I don't think I'd buy over sized valves as that is just more weight in the valve train that will ultimately hurt performance. I'd end up buying new stock size valve and new stock size guides. Hrmph hrmph hrmph!

[ryan roopnarine]

oh wow. i just checked the factory service manual (not bentley) and it said to refer to the assembly service manual (not even as much as the bentley excerpt dave posted) for the information you need--unless i didn't check carefully enough.

[George M]

Thanks a lot guys. I agree with both of you that they are a bitch to deal with. How does one actually install the guide though? Do I need to get them pulled and pressed in? I don't want to do them unless necessary - my oil burn could be valve seals as they are most likely the culprit. I don't think I'd buy over sized valves as that is just more weight in the valve train that will ultimately hurt performance. I'd end up buying new stock size valve and new stock size guides. Hrmph hrmph hrmph!
Quite certain the guides if removed are machined out Jon and then a new guide with slightly larger O.D. is pressed in place. Here is the tradeoff...modest increase of valve mass/inertia due to modest oversize of valve stem...very slight...versus difficulty of removing and re-press in of replacement guides. This is why...quite sure Bill R wrote about this a year or two ago...per the TIS that BMW endorses ream of the existing valve guide and replacement with a slightly oversize valve stem. I am quite sure this position is due to the difficulty if not lack of consistency of pressing back in replacement guides...interference has to be right on the money...enough for retention i.e. guide coming out or becoming loose and not too much interference to split the head when pressing in...or reducing the I.D. of the guide due to excessive press. The third issue is that of perpendicularity and being concentric to the centerline of the old valve stem....takes precise machining that the factory can best control with their fixtures. If you think about it...it makes a lot of sense...at least to me. All is acedemic of course if your guides and valve stems are within the acceptable range of wear. You need to determine this to decide your course.
George