checking valve guides on carrera in car

[captainlewis]

I am looking at vehicle to purchase. I have concerns about valve guide failure I am looking at 120K miles cars , Carrera 1984 to 1988. I was told by a technician, that if you remove the lower valve covers (exhaust) set a dial inicator up and force the valve stems radially that a clearance value of 2 o3 thousands is good and that 7 or 8 they will need attention soon. If this really works it would be very helpful. Aslo I am running into cars that are said to have had top end work with no receipts. In theory if the rings had been done recently what would a good leak down % reading be and what is starting to be marginal. I realize tht a leak down will not tell me about guides. Any expert help would be of great asistance, thank you JL

[mnmasotto]

I recently had a top end done on my 1987 Carrera. The best way to tell if the valve guides are bad is the amount of oil the car uses. My oil consumption rate went from 800 miles to 400 miles per quart in about a year. I have been told by many that valve movement back and forth is not a accurate way to assess you valve guide health.

I would bet that at 120K miles the valve guides are like a pair of lungs in a patient who has smoked two packs of cigarettes per day for 30 years. Toast!

[stormmaster]

Mine lasted just over 100k......had them replaced....word of advice....if they haven't been replaced, plan on replacing them. While you have the engine apart I also suggest replacing the head bolts....it will save you some money in the long run....ask me why I know this.....

[john walker's workshop]

you can fairly safely assume that there will be some guide wear at 120K. i've done VGs at 60K, although rare. carreras seem to need it sooner than SCs. wait too long and the seats get beat up pretty bad. the price should reflect the need for a $4k repair. a quart in 300 miles is not good. there may be some crusty buildup on one or more plugs if it uses that much oil.

[cgarr]

At 120k you can assume it needs them and without records you can also assume it needs them. I would plan on that going into the purchase.

[911st]

I was told to take the car out after warmed up. Take is up to 5000 rpms and close the throttle. If it smokes on throttle lift, the guides are bad. May have to have someone else follow or drive the car so you can watch. If it is bad, you may see it out your mirror.

At least, that is what I have been told by a good Porsche specialist with a good reputation. This seems to be the only info I could use other than oil consumption.

Interested on others thoughts on this.

[Por_sha911]

The measurements you are referring to will not guarantee good guides although too much play will mean bad guides. If those are the original guides at 120K there is probably a top end rebuild in the future. What 911st said about smoke after lifting is true but, as before, no smoke doesn't guarantee a good motor.

Do a PPI and get a leak-down test. NOTHING replaces a thorough PPI and it is money well spent.

[911st]

I bough my 3.2 about 6 months ago and was very concerned about exaust guide ware with 130k miles on the clock. From what I have heard, a PPI is not going to be able to effectively assess the valve guides. I took my last purchase to the best shop in the area and one with a national reputation and SCCA trophy's and asked for the test referred to above with the dial indicator and they did not think much of it.

I am not willing to make assumptions and hate to take down a well running motor just because some say 100k is the failure point.

The tests I have heard of are: the dial indicator side load test; educated ear: and high rpm lift test. None are perfect. Smoke on start up is not valid. Oil consumption might be the best but as a buyer you will not know.

I wonder about the looking at plugs or peaking in the ports with a scope as a valid test.

Just dose not seems to be any stand outs in assessing the exaust guides.

I have done this a bunch of times and I just wonder if I should not just buy em and just go ahead and take em down. It seems that by the time I get done paying for a good PPI, having a service with valve adjustment, and chasing leaks, I typically end up $3k into them anyway. That should not be to far from the labor cost for a top end anyway.

[porschenut]

Oil consumption isn't really a good indication either because there are other reasons why your oil consumption may be high. Bad rings? You betcha.

And how much is really being consumed vs. being leaked out? You'll never be able to tell.

At 120k, I would never do just a top end. At that mileage you'd be wise to go all the way to the crank.

[captainlewis]

That is what I am looking for, the side movement dial indicator is what someone told me. Most ppis just don't diagnose the guides. thank you JL

[john walker's workshop]

Originally Posted by porschenut

.

At 120k, I would never do just a top end. At that mileage you'd be wise to go all the way to the crank.

on a chevy maybe but not on a 911.

[craigyirush]

John, a question - if the oil consumption is bad, say below 500 miles/quart, would you always see it on the plugs or have blue smoke out the tail pipe?

I am watching my oil consumption closely - 205K on the engine, no idea what's been done if anything. It's currently using about 700 miles/quart, which I am not happy about, but it never smokes on hard accel or decel or even on start-up.

[Dynamohum]

Originally Posted by captainlewis

I am looking at vehicle to purchase. I have concerns about valve guide failure I am looking at 120K miles cars , Carrera 1984 to 1988. I was told by a technician, that if you remove the lower valve covers (exhaust) set a dial inicator up and force the valve stems radially that a clearance value of 2 o3 thousands is good and that 7 or 8 they will need attention soon. If this really works it would be very helpful. Aslo I am running into cars that are said to have had top end work with no receipts. In theory if the rings had been done recently what would a good leak down % reading be and what is starting to be marginal. I realize tht a leak down will not tell me about guides. Any expert help would be of great asistance, thank you JL

I purchased a 87 with a 140k and though ran great and showed no smoke on start up or from throttle lift the guides were worn out.

I preformed the same test listed above which confirmed that the guides were worn out. With the valve in the open position so that it is off its seat, it does not take much side force to overcome the spring tension and you can visually see the wear. Mine were so bad, the movement so obvious that I did not need to use a dial gauge. The time and and effort to do this test is minimal, it might not tell you every thing about your valve and guides but its a good starting point.
Chances are they are worn out with that mileage.

[john walker's workshop]

[John, a question - if the oil consumption is bad, say below 500 miles/quart, would you always see it on the plugs or have blue smoke out the tail pipe?

I am watching my oil consumption closely - 205K on the engine, no idea what's been done if anything. It's currently using about 700 miles/quart, which I am not happy about, but it never smokes on hard accel or decel or even on start-up.]

it probably had work done before you got it. i wouldn't worry about a qt in 700 miles. no smoke on a cold start is unusual. must not be a 911.

[Brother]

Originally Posted by porschenut

Oil consumption isn't really a good indication either because there are other reasons why your oil consumption may be high. Bad rings? You betcha.

And how much is really being consumed vs. being leaked out? You'll never be able to tell.

I'd think you would have plenty evidence of a leak.

Otherwise, both of the other reasons are a reason to at least look at the heads on your way to the rings.

[Brother]

Originally Posted by john walker's workshop

on a chevy maybe but not on a 911.

I always assumed that it would not take much more to replace the main bearings and other case hardware. Maybe this is too many years of watching others go through while you were in there sickness.

What is the cost difference between a top end and a full overhaul(top and bottom)? Assuming you can you rering and not replace pistons or cylinders.

[Dynamohum]

Originally Posted by john walker's workshop

on a chevy maybe but not on a 911.

I agree a 100% with John,

With a 140K on my motor, I was getting nervous about the bottom end. I decided that it would be wise to tear it down and do a full build while I had the heads off. Once apart I plastigauged the rods and main brg and found that they were still well within spec.

So Lesson learned, I could of just done the heads and timing chains and been done with it, saved my self a ton of money and drove the car for years before actually needing the bottom end done.

But then I seem to learn everything the hard way

[porschenut]

Originally Posted by Dynamohum

So Lesson learned, I could of just done the heads and timing chains and been done with it, saved my self a ton of money and drove the car for years before actually needing the bottom end done.

Yeah, but not everyone's car is the same as yours. Some are treated better than others. Let's face it, some 911 engines last for 400,000 miles, and some are done at 100,000.

My point is, until you get in there and do it, you don't really know what condition your motor is in. In my opinion you did the smart thing. Since you've got the thing down to a short block anyway, at 120k miles, I'd rather spend a couple thousand more and be sure of what I have than risk having to do it all over again a year or two down the road. This is especially true of cars that have had multiple previous owners, and who knows how they've treated the poor thing?

Do it all just once, and it will probably last longer than the supply of gasoline to put in it.