Excessive exhaust valve guide wear

[GA CYCLE RIDER]

Since I have my 05 22k mile ticker in the shop for head work right now I had some spare time to delve into the problem a little deeper. My idea was to "google" the phrase in quotation marks, "excessive exhaust valve guide wear" and see what kind of information popped up. This is what came up on the first couple of selections. A porsche club was reporting that a high number of 1989 and up carrrera 2/4 models were winding up in shops with worn out exhaust valve guides. The problem was determined to be caused by build up of extreme temperatures in the heads. The build up of the high temps was traced in part to the engine under pan that would not allow the heat to escape. Some of the groups who participate in Porsche racing events have advised removal or altering this pan to allow for extra cooling. The 06 FJR that has the various changes, including the ventalation and radiator system may avoid the curse of the tick by managing internal engine/cylinder head temps better than the 03 through 05 models. The FJR's cause may be more related to heat managment than an outright engine design flaw. Who knows that if Yamaha ever put the FJR motor in a naked bike that it would ever develop the tick because it is out in the wind. Maybe one day we might find out.

 

[radman]

What may be significant is that the Porches are air cooled, the Feej is not.

 

[GA CYCLE RIDER]

What may be significant is that the Porches are air cooled, the Feej is not.

The year models being discussed are air cooled along with the help of a huge oil capacity. Not sure of the exact amount but I believe it is more than ten quarts. Dont hate me if Im wrong. The thing that I found to be similar was the fact that the heat that was being produced in the combustion processes of both the FJR and The Porsche had a difficult time in escaping and therefore allowed the temps to possibly rise to a point that was high enough in certain vehicles to cook the guides. Lucky for the owners of later model P-CARs that they now have water cooled engines.

 

[radman]

The guide problem was examined in every way possible by the tech heads when it started to occur. It was maddening to discover that it occurred in northern climes as well as southern, well maintained bikes as well as SkooterBrand® Schedule aficionados, rural bikes, city bikes, etc. That it was heat related was dismissed fairly early on; after many cooling mods were attempted, none of which appeared to make any difference. Though the Feej tends to be a hot machine when temps are high, these affect the rider more than the machine, as it turns out, the FJR has pretty decent engine cooling management, if it didn't, more heat related problems would have cropped up-as it is, many are hitting the 100,000 mile mark, and, with some exceptions, appear ready to go well beyond that milestone, not something one would see in an engine with inherent cooling issues.

 

[jestal]

Where exhaust valve guide wear and heat are concerned the issue is generally related not specifically to the heat itself but to the distortion of the exhaust valve guide due to the heat. Since one end of the exhaust valve guide is hanging in the exhaust stream/exhaust port and the middle is surrounded by solid aluminum and the other end is exposed to engine oil the guide is heated to a variety of temperatures along it's length. This temperature gradient, along with the expansion of the material (being different at the different tempertures) causes the guide to "warp" along it's length. That is where the length of the guide, the clearance, the guide lubrication, the guide and valve surface treatment, etc. all come into play to enable the valve guide to live and not scuff and score due to the reduced clearance brought on by the warping of the guide. If you think of the valve guide as a long thin cylinder under perfect conditions then it will go "banana" shaped under operating temperature. If the clearance is sufficient to allow this without trapping the valve then all is fine. If the distortion overcomes the clearance then the valve material/guide material/lubrication/compatibility/etc. all become critical. If metal to metal contact occurs the valve/guide will scuff and score and the material transfer will cause one to act like a file on the other and "loose guides" results. If one eliminates the metal to metal contact or improves lubrication the situation becomes more liveable. Often shortening the guide will help as well as counterboring the exhaust guide from the port end to reduce the interference in the hot area of the guide. Added lube with the "wetter" seals also helps with lube and cooling of the guide.

Air cooled engines really have an issue with exhaust guides and exhaust guide wear due to the difficulty cooling the guides adequately and getting air around them to cool them directly. That is where a particular engine builder can have a profound positive or negative effect on valve guide wear with setting the clearances, effective length of the guide, valve material selection, etc. Often, sodium cooled valves are required in those cases to carry the heat out of the head of the vavle and past the guide with longer stems or simply the exhaust valve guide clearances must be increased significantly in anticipation of the high temps and large distortion expected under load. Typical case of what works good for racing is not good for passenger cars or vice versa.

As a side note....those air cooled Porsche engines do rely on oil cooling to some extent as well as do many engines for critical areas. Oil cooling capability is NOT improved by adding oil capacity as one might think. Oil coolers, heat transfer from the oil to the coolant via oil/coolant jackets in the engine, etc. all help reduce oil temp and oil cooling capacity but just adding oil volume does not help cooling per se. Added oil volume does add significant thermal inertia...i.e...it takes longer to heat up 11 quarts of oil than it does 6 or 7..... but it will not affect the final temperature of the oil if the engine is held under load for extended periods. Admittedly this may be a fine point as most of the very high output engines just run at full load for brief intervals so the effect of the added thermal inertia of the large oil capacity does serve to reduce average oil temp but technically the extra oil volume is just a heat sink that can easily be saturated and does not ultimately help oil cooling in its strictest sense.

Also, many of the performance oriented Pcars have liquid cooled cylinder heads only with the cylinder barrels air cooled still......

Since the FJR is liquid cooled and the liquid cooling system seems very adequate it is highly unlikely that blowing air on the motor would affect the exhasust valve guide issue. The aluminum of the head and engine block is very conductive and will run at or near the coolant temperature pretty universally so blowing air on the outer surface wouldn't affect any thing. In any case, the outer surface of the engine is seperated from the guides and functional surfaces by the coolant jackets so the temperature of the outer skin of the engine has little relevance to the internal tempertures along the valve guide.

 

[Bounce]

interesting comment on oil volume affecting temperature inertia. once it's heated it would take longer to cool back down (excluding an oil cooler to speed the process).

thanks for the thoughts.

 

[Ignacio]

I did some checking a couple of years ago closer to the Feejer and found that the air-cooled Yamahas used in Outlaw and other classes of races cars were having valve and valve guide problems too.......specifically in a couple of cylinders, but talking with the one of the national engine builders they confirmed it was a problem on the aircooled engines and not water cooled. In their case they were mounting engines longitudinally and the two cylinders closest to the exhaust pipes were getting cooked.

Their answer was mostly from a materials perspective and through the seals. Changing guides to an oil impregnated bronze higher quality material coupled with a slightly looser valve seal. Seems Yamaha went with the latter as a fix on the FJRs.

I concur on the air vs. water cooling. Apples and oranges. Hot spots are either totally eliminated or virtually eliminated by a circulating fluid design. The only difference could be if there are obstructions or flow coolant flow irregularities.

 

[Constant Mesh]

Does the ID of the stem oil seal grow larger over time due to wear?

Does the stem oil seal have a break-in period similar to the metal parts of the engine?

I've often thought that those who haven't had a ticking problem may have ridden their bikes fairly gently during the break-in period. By gently I mean they never ran them at high power levels or high rpms, even briefly. This would allow the seals to wear a little and open up before higher localized temperatures and rpms were experienced. With the seals opened a bit more oil droplets would flow down the guide.

 

[jestal]

Generally speaking the valve stem seals shouldn't change during breakin..i.e...they don't breakin themselves per se. The elastomer seals are pretty stable and really shouldn't change in operation. As the guide might wear due to various reasons the valve stem starts to move around more that causes the seal to pass more oil but the current crop of valve stem seals are pretty stable and durable.

 

[FJR919]

Thank you again Jestal. I always enjoy reading your view of the technical issues that pop up on this board.

 

[CherokeeKid]

A quote from my head overhaul guide:

"I also noted during valve inspection that the stock exhaust valves are bi-metal. The lower half of the valve is SS and the upper half is carbon steel. The SS is more durable to hot exhaust gases and the steel is more tolerant to mechanical wear from the constant impact of the cam and lifter. The Yamaha valve is fused in the middle, meaning that the seam is half way up the stem. This places the fused seam inside the valve guide. (I question this design, as the heat transferred up the valve stem must cross this fused boundary.) Also, the seam creates a ridge that can wear on the inside of the guide. This seam can be felt with your finger nail on the old valves.

A more common approach used by other valve manufactures is a SS valve and stem with a Stellite tip welded to the top of the stem. The Stellite provides a hard wear surface over the softer SS metal but eliminates any fused boundary inside the guide area. "

In the quide is a picture of the old valve. I have tried to get this guide published on a web site so anyone interested could download it. Three different forum members have requested a copy of the 22 page guide with a promise to make it available to the qroup. So far no results.

If you are interested send my an e-mail.

 

[radman]

Having recieved the above Guide from the kid, and reading through it, I would suggest anyone contemplating this job, or even having a tick repair done, get it and read it. Very nice job, thorough, and complete.