rusnak

That's what I was told by my friend's smog test dude yesterday.

I got a call from a rather bummed out buddy who owns but really can't afford to maintain his 911SC.

He failed smog, with the HC numbers not surprisingly off the charts. Bad miss at idle ( I suspect cyl #4 is not even burning gas). Ignition system fine, but obviously the cat is toast.

The tech told me that a valve adjustment might help. At first I thought no way, if the valve(s) were (are) not closing, then wouldn't the piston hit a valve? Then I started thinking about the SC pistons. Aren't they flat-topped? Is there enough clearance/ deck height to allow one valve to remain open and not blow up the motor? Maybe one valve is already cracked from having already hit a piston at high rpm?

Time for a leak down test, but he doesn't have a compressor, and I don't want to tell him to drive to my town, which is probably 40 miles, just to have the car blow up on the freeway. Not sure what to tell him.

ivangene

thats a sad story - I can relate to the "cant afford" aspect when it comes to a "major repair"

I think the best thing (if his top end is toast) is to tell him its a chance to learn. (hopefully he has a second car and a garage) he can spend a year or more and really learn about his motor. There are lots of things that should not cost much (cleaning parts ect) to take up time and when he has money to replace bad parts he can just start getting them

its not much, but as someone used to say to me "it is what it is"

hope its something less costly for him

theiceman

Wow that is bad news ,, did he do a money shift at some point ? sure sounds like it. My guess is a valve is bent and is not seating. or busted. Time to pull the head and have a look I guess.. leakdown would be the way to go though for sure

Carlo_Carrera

Wow that is sad.

Your buddy could easily try adjusting the valves himself, but that most likely will not help, but it should be done first.

whalebird

Leakdown is your (his) friend here. If a valve were to tighten up enough to hold open, you would have had problems a while ago, it would eat a cam lobe and/or a rocker. More often than not, a valve/piston collision results in a brocken rocker, so maybe, just pulling the valve covers would speak volumes - maybe. I would most definitly get a second opinion on the compression/leakdown. It's like a PPI, get a knowledgable opinion on the status of the engine, it very well may save you thousands in the long run.

theiceman

I have a somewhat ( read that as totaly NOT ) related question. I have a compressor .. how hard would it be to make my own leak down tester .. anyone ever done it ? figure I might need a guage some tubing and some kind of threaded hollow rod with the same fitting as a spark plug.

GMS

$40 - $70 (US) to buy new is why no-one bothers to make something you can buy with a click off the web.

whalebird

You could make one pretty easy. I would say buy one of the budget variety. The gauge and all related plumbing should not be outragious, maybe you could borrow or rent one. One thing is that you have to "zero" the gauge once you apply pressure from the compressor. As you get TDC for each respective cylinder, you may want to reset the "zero". In other words, if your compressor is not large in capacity, when you jump from one cylinder to the next, the differential pressure drop (from releasing pressure into the cylinder)will skew your results. Halfway thru the test, your pressure in a small tank could drop 50%, then the compressor kicks on, all along creating variations in your "base" pressure. I think a dedicated leakdown gauge will read in %. A simple psi gauge would have to be correlated to %. Also, its nice to have a shraeder valve in the line so your readings can be held, released, then reapplyed. You want to be able to aplly the supply pressure, quick release the supply hose without losing pressure out of EITHER end(supply/cylinder) of the gauge. You could probably rig up a quick and dirty apperatus to get an idea of whats going on. You also want a mechanics stethascope; remove the metal probe and just dangle the open tube and listen for air rushing into the oil tank(crankcase - rings), muffler(exhaust valve), and intake(remove air filter, for intake valve).

theiceman

hmmm wonder if I could build one in the 4- 7 $ range ...

rusnak

I think the hardest part would be the middle section, which is like a manifold.

I have a leakdown tester, and my plan was to incrementally raise the pressure up to test value, so as not to bump the piston off TDC and start the motor a-spinnin.

The problem is that I dont really want to load up the compressor, take it all the way out there (about 40 miles away) if I don't have to. Maybe I can take the air regulator off of my compressor and just take it out there with the tester. Still, some gas station wouldn't want me to mess with their air lines.

The last time I saw the car, about a year ago....it had bad injector seals. He probably has been running the car lean ever since then.

I think he probably dinged a valve in Cyl #4 against a piston. I suspect the spark plug threads are stripped in Cyl# 3 because he did his own spark plug change, and the tech guy says that there might be a few good threads left......overall, this motor might have had it.

Brett San Diego

I wonder if he should even spend the money on a leakdown test. Sounds like with that bad a compression number, you'd be pulling heads and doing a complete top end anyway.

Brett

rusnak

He doen't have the money for the leak down test, nor a valve adjustment, which is why yours truly got a phone call......

I feel bad for the guy. I mean, if by some miracle a valve adjustment is all it takes, I'd do it myself. But I think it's a bent or damaged valve already, as WB says. I just don't think the piston would have not already hit the valve, and obviously there is a BIG leak in #4. Just to do the leakdown, he'd have to drive all the way out here if I were to do the work in my shop in my spare time. But that would mean driving the dang car. Not good.

Ed Hughes

When did he change the plugs? Just prior to the test? There's always the chance that there was a bunch of carbon that got knocked loose and is keeping the valves from seating.

For the record, I can attest to the fact that you can bang a bunch of exhaust valves into pistons and not break any rockers.

race911

Driving it is unlikely to do any more harm. I mean, this just "didn't happen". So it's been in this running state for awhile. I don't remember any of the POS 2.7s I used to rebuild having bent valves and showing any compression in that hole. Unfortunately, no easy fix. If the guy doesn't have any money, he doesn't have any money. There's no free lunch with these, and absent having inventory to plug something else in...........you either fix it or sell it for what you can get as-is.

Tango635

You know, in my opinion, hard times make people very resilient and very crafty. I like the "take this as an opportunity to learn" approach. I hope your friend can do that.

I'm sure you've heard of sayings like, "to move a mountain, you first start by moving a rock" or whatever. It can be done. It may take some time, but it can be done!!