R90/6 Exhaust Valves and Valve Guides

[banzaibob]

Preparing the R90/6 for the winter rebuild/Seibenrock kit. It was down on power and also smoked quite a bit on start up. Compression was 145 psi on left and 125 psi on right.

Today was disassembly day. Everything actually looked pretty darn good. The best news is that the smoking and reduction in power question was answered right up front; ring end gaps on both cylinders were close to .030" on some rings. The real problem I'm having is trying to make a good evaluation about the valves and the valve guides.

Both intake valves, valves guides and seats are all in good shape. There is hardly any play or "wobble" in the valves/guides. The exhaust valves are more problematic. The seats and faces don't look bad at all and could probably just use a good lapping (I'm probably going to regrind though). However, I am having difficulty gauging clearance between the exhaust valves and their guides. Sitting loose in their bore, there is a good amount of "wobble" or lateral movement. Both exhaust valve stems measure 7.94mm and 7.93mm. Any tips on measuring the I.D. of the guide so I can determine clearance?

Do the valves need replacing? Should I replace the valves and valve guides together? Is it possible to get a valve guide slightly undersized and hone or ream it to size? What would the BMW gurus do?

 

[barryg]

The exhaust valves are used up and need to be replaced. A lot of machine shops ream the guides to size. This process is very crude. The best way is to hone inside diam. to size. This gives a very accurate and true hole the length of the guide. When I was doing heads this was the procedure I used. This procedure allowed me to run the tightest clearance possible. This gave the customer longer service life for his heads. With new guides installed the seats need to be machined. Good luck with your heads.

 

[banzaibob]

Any recommendations as far as a supplier or brand? Does anybody offer valves and valve guides together as sets?

 

[Dmftoy1]

How many miles on the bike, and any idea if the heads were done previously? If they've never been done I'd probably have new seats, guides and valves installed to make it "unleaded friendly". (That's what I'd did on my 74 r90/6 last winter. Ymmv. I think most folks are using black diamond stainless valves now but I'd have to check my paperwork to be 100% sure

 

[20774]

Snowbum has an extensive article on valves, seats, and guides here:

http://bmwmotorcycletech.info/valves.htm

 

[manicmechanic]

Personally I would not consider the Black Diamond valves. There is member of this forum, James A, who had a very bad experience with them. I have two sets of heads, one set installed, one on the shelf, that have been rebuilt using stock parts (valves, guides, seats). The installed set is working well for me.

 

[AntonLargiader]

If the stems are consistent along their length, they don't sound bad. I get 7.945 for new ones. Guides normally come undersized and are then honed to fit. If you bought BMW guides you would probably find that they need little or no honing, so you probably want to get guides elsewhere.

Have you ever changed guides? You need to be able to adjust the OD to match the head and the ID to match the valve and be straight after installation. If you're up for that, call Beemershop and tell Ted what your valves measure. He can probably supply guides with enough meat to give a good fit after you hone.

 

[banzaibob]

Both exhaust valves actually look very good. Their length is well within limits. The faces look great and show no signs of cupping or "tulip-ing." I have actually looked at the Black Diamond valves on their website. They list stem diameter at .3125 which is 7.94mm (what I have already!). I do not know if it has hardened valve seats but the bike has in excess of 60,000 miles and all exhaust valve components look as if they could be simply lapped in and go another 60,000.

Except for the guides. Although they don't show any outward signs of wear there is that lateral movement. I do not have the tools to attempt replacing the valve guides. The cylinder head specialist that I use locally would need me to supply him with the replacement guides. After measuring the O.D. of the top of the valve guide should I just buy the first oversize (where?) and take it all to him using the old valves?

 

[AntonLargiader]

There are specifications for all of this stuff (stem clearance, guide interference in head, seat contact, spring height, etc.). I don't want to give you an incomplete picture so I'm not going to start. He should have access to this information or you should find someone who does.

Even if you weren't replacing the guides it's wrong to think that they would benefit from being lapped in. All you'd be doing is using one worn surface to further shape the other, which is what's been happening for 60,000 miles. And with the new guides, especially, you need freshly ground, concentric surfaces. It takes so little time to do this right, if you have the tools.

Isn't there a BMW-experienced shop near you?

 

[barryg]

There is nothing wrong with using Black Diamond Valves; I've installed quite a few with no problems. Most likely you need to pick a shop to do the work and let them decide the parts you need and the procedure for the headwork to be done. That's their Job.

 

[20774]

You would think that Engle Motors in Kansas City would be a good source for Airheads.

 

[banzaibob]

Therein lies the problem; The local BMW shop knows BMWs but would charge out the ass. The automotive machine shop that I've used for the last 10 years rebuilding heads from Honda trail 90s to Norton Commandos charges more reasonable rates and would do only what I insist they do. In this case, it would be re-using the old valves and seats and simply installing new guides. They of course would re-grind face and seat and while I was at it re-grind intake also.

I contacted the Beemer Shop guy about the head work and he quoted me a rough figure somewhere slightly north of $500 for the works. I really like this bike and all, and I want this Seibenrock kit to work well but at some point I have to be pragmatic and think about the money going out. At this point and from my perspective the only thing wrong with the cylinder heads is sloppy exhaust valve guides. When I spoke about lapping the valves it was more toward illustrating that the condition of the heads in general in good and usable (except for IMHO, the exhaust valve guides).

With the big bore-high compression kit installed I realize that things become more critical. Since the bike is not going to be raced, is total reconditioning of the heads/valves/etc. worth the additional expense?

 

[banzaibob]

Yes, Engle is good and worthy.

 

[AntonLargiader]

I contacted the Beemer Shop guy about the head work and he quoted me a rough figure somewhere slightly north of $500 for the works.

You were asking for a supplier of valves and guides; that's why I suggested you call them. I probably have some guides if you need them. Will try to remember to check on Monday.

Still, if you are calling the shots for your cylinder head guy then you need to really own the information you give him.

 

[james.a]

Personally I would not consider the Black Diamond valves. There is member of this forum, James A, who had a very bad experience with them. I have two sets of heads, one set installed, one on the shelf, that have been rebuilt using stock parts (valves, guides, seats). The installed set is working well for me.

I did have a bad experience with Black Diamond valves. What I later learned is that they are not compatible with OEM guides.

As barryg notes, a shop that specializes in Airhead motors should know this. I learned the hard way by using a local machine shop and following the recommendation of a well know dealership whose parts desk was pushing BD valves as a low cost alternative. The weak link of that chain was me. Anton's post above is perfectly correct.

 

[AntonLargiader]

The only problems I'm aware of with BD valves is that there was a time when the keeper grooves were not hard enough and they mushroomed. I think that is way in the past (and I have seen it happen on other valves also). Most of my customers ask for OEM or OEM-type valves but at this point I am not avoiding BD.

 

[banzaibob]

Come tomorrow morning I am going to run these heads and valves down to the cylinder head guy I've always used (Noland Cylinder Head KC,MO). Although they are not BMW specialists I do not believe there has EVER been anyone locally who has had a complaint about their work. I will report my findings.

 

[typ181r90]

I had Tom Cutter re-do my heads years ago and he used Black Diamond valves and Ampco valve guides. I heard the horror stories about BD valves (only on airhead forums btw) and he dismissed it as only a couple early cases of failure being made into a bigger deal by the internet. I was willing to pay for the BMW valves and he said he'd actually heard the current ones you can buy were prone to failure, go figure...

All I know is they've been serving me well for years now and I have nothing bad to report as of yet. My buddies that run old Triumphs also redid their heads using BD valves and they have no issues either

 

[20774]

There must be some back and forth on products and quality. In August 2011, Tom Cutter posted on the Airheads list that he doesn't use BD valves with Ampco 45 guides as the guides are silicon bronze. In July of this year he stated that the BD valves don't work well with OEM silicon bronze guides but he uses a non-OEM guide better suited and machined for use in the Airhead engine. So, this is one of those situations where it can be important to rely on the experience of the mechanic doing the work on your heads.

 

[banzaibob]

In case anyone is interested, here's where I am on all of this: Took the heads to Noland Cylinder Head in KC. Their top gurus said that the valves all look fine. Intake valve guides were fine. Exhaust valves guides, not so fine. They are going to regrind all faces and seats and replace the 2 exhaust valve guides (I will have to supply the guides, Engle Motors says they have them in stock). It will cost around $180 (tops) and take about a month.

I also explained to them that I am putting larger, high compression pistons in the bike. They didn't see any complications from that and stated that BMW motorcycles from a machinist's perspective are "easy." If this is anything like work I've had done in the past it should be the last time I ever have to worry about it. Wish me luck and hope I don't screw anything else up.