cobalt

I was attempting a valve lash adjustment on a late version 91 engine with 120+k miles. The car has not had an adjustment in 50k miles, although there was no noise and the car was maintained properly otherwise. It has some old seals needing replacement prompting the engine drop. Leak down shows solid numbers of around 4-4.5% per cylinder. I had noticed that there was no play in any of the rockers as you can usually feel with proper lash adjustment so my initial conclusion was they were too tight. Cylinder #1 intake I had a problem getting repeatable results using Steve Stomski's tool. Kept changing but finally got an acceptable number so I felt. Exhaust was far easier done quickly so I moved to the next cylinder. This time numbers were all over the place. One push and I get a reading of .004 then as second try .011. A third .001. I noticed some odd movement so I removed the intake rocker and what I found was not good news. The bronze bearing surface along the bottom of the rocker was worn considerably as much as .030" in some places but along the bottom. Depending on how the rocker moved on the shaft changed the numbers.

So Looking at the price of new rockers sticker shock set in. Nearly $3k if you replace everything using all factory parts at list. Thankfully you can buy an inexpensive bearing sleeve and fix the issue relatively cheaply. Some parts can be salvaged but those are relatively cheap so why not use all fresh. At least no need to scrap out $1750 in rocker arms.

What I found interesting is the wear is primarily only the intakes with barely any wear on the exhaust. After discussing it with others the conclusion seems to be an oiling related issue since the rockers rely on splash oil. There is possibly some blame on the lack of adjustment and possible tightening of the lash gap although very hard to say if it was related or not.

Just thought this would be of interest.

Here are some pictures of a new rocker vs the worn ones. Also lined up so you can see the area of wear.


New rocker



Worn rocker



Worn rocker placed over new to show wear area.

Rocket Rob

Wow. Thanks for sharing. I would have assumed this was an oiling issue, not a lack or adjustment issue.

Spyerx

I suspect running too tight caused excessive wear over time. Possible poor quality oils.

You can get the rockers reconditioned too. Pretty sure Ollie’s and others do it.

Bummer

cobalt

He was pretty diligent about oil changes and used M1 15w-50. Rockers are fine just need to replace the bushings which is easy enough to do. No visible signs of damage or wear on the rockers or cams, rocker shafts have some marring which can be cleaned although we will inspect and replace if needed. We will also replace all tappets which have too much play in them. Otherwise this engine at 125k miles with all new seals should last another 125k miles if this is all the wear we find.

wallra

that's the problem mobil one don't have the zink. I talked to Steve Warner about this and he told me he didn't see it coming.he had cars coming in with camshaft wear. you start to see valve train wear and cam shaft wear. It's not just porsche engines I'm see it on. all the old stuff.

-nick

M1 15w50 has plenty of zinc. The zddp content varies between Mobil1 weights. Someday this rumor will die, but that day is not today

This is a Jersey car? Potentially driven regularly in the dead of winter with that thick 15w50? That's all that I can think of.

I had Dougherty cams rebush and resurface my rockers for a nominal fee. If the bushings are that bad, I expect the surfaces aren't great? How about the cam lobes?

Navaros911

I thought the 15w50 was not too bad though?

For it to be linked to the oil I think we would need more data points... which not so easy to get without a test lab to compare oils under thebsame circumstances.

evilfij

I have no idea if this applies to 964, but over time in my experience with old engines, valves tighten and, if not adjusted, can cause rocker wear (among other issues). I don’t see why it wouldn’t apply to a 964. Anyway, I would lay it on lack of proper adjustments.

cobalt

It is definitely a combination of too tightly adjusted valves and the fact it is oiled by splash oil. All the valves were excessively tight but only the intakes showed the extreme wear. So how much of it is the tight valves I can't say. Since the exhaust valves were equally tight but sit closer to the oil I am assuming that they suffered less wear due to it getting more oil. The car has seen 10k miles in 3.5 years it really doesn't get driven much in the winter. I will discuss with the owner what his start up procedure is if the car sits for any length of time. It is possible the wear is associated with tight valves and not building oil pressure after sitting. I measured everything I could using Stomski's tool and a dial indicator which reads to.0001" I see no wear other than the bronze bushings which are being swapped out with new and the tappets which are sloppy from the force. I think we caught this one but as a public service I think we all need to consider how we start a sitting engine and consider how often we check valve lash. You won't hear them tapping if they become too loose, you would need a considerable amount of slop to hear anything and more likely they will tighten from all the pounding against the valve seat. We did not see enough wear to change the leak down which was fine if it was leaking through the valves from being excessively tight it could lead to all sorts of other issues. The fully closed valve helps dissipate heat if it is ever so slightly open it won't do its job and then it will be game over soon enough.

Catorce

Don't bother reconditioning rocker shafts, my cost on those (and anyone else who has a wholesale account) is less than $20 each.

cobalt

Please share I have access to worldpac, northside and a few others at first tier pricing and IIRC they are a bit more. No doubt MSRP markup is stupid money at times the rockers themselves have very little markup and are cost effective to repair. Cost to recondition is considerably less and my guy is doing it as a package deal. So it is worth just having them done since the cost is relatively nothing. But thanks anyway.

dutchcrunch

adequate Oil can’t migrate into an excessively Tight space when a splash application is used, hence the wear.

dsan

I'm sorry, this is way past my skill level to contribute but I do have a question regarding this quote. This is something I've been thinking about for a while. With my recent rebuild it's come back into my mind and figure you guys are the right people to ask. How long of a time frame do we consider an engine to be "sitting"? I only get to take my car out 1-2 times a month and pull my fuel pump fuse to build up the oil pressure but I'm wondering if that is overkill. The valve lash I check roughly every 3rd oil change (<10,000> miles or 3 years) but always wondered about what kind of time frame we talk about regarding a sitting engine. 1 week, 1 month, longer?

I hope this question doesn't throw off the topic too much, so far this thread has been a great read.

cobalt

I agree it isn't the best method but was used by Porsche for nearly 30 years this is the first I have seen with such extreme wear and although it hasn't been on my radar i never had an issue adjusting lash on other engines like this so I am assuming the wear did not exist because they were adjusted more regularly. I think it is a combination of too tight of an adjustment or no play at all and lack of oil.


I think it is a bit overkill others may disagree. I usually do it if it sits for around 4-6 weeks. Although some say better safe than sorry.

cobalt

SO it was a simple repair but could have been far worse. I cleaned and checked the oiling tube to make sure there were no issues which it appeared there weren't any. My guess is this has a lot to do with sitting for months and not properly starting the engine getting oil up towards the rockers by cranking it without the DME along with overly tight valve lash adjustment.

All better now new bushings, holes drilled sized and rocker shafts cleaned. Sorry for the bad photos they looked clearer on the phone screen. All this for less than the cost of a new rocker shaft each albeit there is labor involved.





Rockers installed and lash adjusted. If all goes well the engine will be back in the car soon. I won't say who but it was suggested that this engine needed a top end rebuild. It only needed the rockers fixed, lash adjusted and some of the primary seals replaced especially the power steering pump seals and pressure temp sender seals which had turned to plastic after 28 years. I did a leak down per cylinder as I did the lash. Because of the slow rotation the numbers were skewed some cylinders initially showing higher than acceptable readings but popping the valves under pressure allowing them to seat properly showed numbers between 4.5 and 6.5%. The cylinders in question had sever intake leaks for at least 50k miles due to prior work most likely causing the car to run improperly due to 2 lean cylinders on one bank. I suspect he has a while before he really needs a top end. For now this was another engine saved from an unnecessary expensive top end rebuild.

In the process of putting it back together and it should run far better without the worn rockers and leaking intakes. The valve covers are mag and were in rough shape but was able to make them useable for the time being. Blasted, acid etched and then used Sikkens acid etching primer and aluminized sliver engine paint. I would prefer he replace the lowers at least but not in the budget so they go back on.


These are some of the seals I was talking about. they just broke apart like plastic.