I was headed to the folks house for Thanksgiving. Stopped to get some gas(200 miles in) and when I stared it up it sounded like something was stuck in the fan or air passagess bouncing around. I shut it down, checked the oil and the pressure was pressure was ok. So I drove it the rest of the way home(about 50 miles).
The noise only came back when I was at idle up to around 1500 rmp. Above that everything was fine.
Would the car still run with a dropped valve seat?
How can I check if I dropped one?
And is their anyway to check the air passages with out dropping the engine?
Thanks guys, I've got my fingers crossed
Samson

I think a dropped valve seat would sound much worse. There are some pics at Pelican of a dropped valve seat. It blew out the top of the case. At the very least, your car would run like crap. More likely that something came loose and is rattling around somewhere under the tin.

If you haven't lost any power, you are probably okay. Did something "crawl" into the cooling fan while you were getting gas? Maybe something fell off and got sucked in?

Beginnings of an exhaust leak. When it cools down make a deal withthe devil and check the exhaust nuts.
I would also pull the valve covers and check to see if everything is correct and tight.

Most Valve seat problems are on the 2.0 heads is that what you have.
A leakdown test should reveal if the seat has dropped.
Sure its not a rod knock you are hearing.

If the valve seat is dropped, you'll know because when the valve goes to sit down, it's ass will hit the floor.

It sounds to me like maybe you sucked something into the fan housing. You would check by reaching into the center of the fan hub (with the car OFF) and maybe even by pulling off the heater ducting part where it attaches to the fan housing and see if there is something in there, I guess. I have had my alternator cover thingy sucked into the fan a couple times, and it sounded like what you described. I've never had a dropped seat, but I'm pretty sure it would make you car run a whole bunch worse than you've described.

Sorry about the smart ass comment, sometimes i just can't help myself.

Exaust leak. Dropped valve seats will cause very poor performance or even a no run. I doubt you be able to drive a car 50 miles with a dropped seat. You would destroy a piston long before that, and have engine parts all over the road.

I actually had a EX valve "head" in my 1.7 snap off and embed itself in the piston crown once.
Made a horrible racket while driving on the freeway, so I clutched in killed coasted off the freewaythen chked everything and then started up agian. It ran rough, there was audible knocking but it ran!
When I took it all apart the valve head had broken into multiple pieces, tore the hell out of the head and piston then largest part emmbeded itself into the piston and was contacting the head on the upstroke. The rest of the valve head I found in the exhaust.

I would agree with the above prolly not a dropped seat. I had one work it's way out but not come all the way. I knew it happened because I could here the piston hitting it. Somehow it fixed its self (good thing I was in the middle of the Alcan. Eventually happened again in downtown Seattle. When I took the head off there was a nice half moon indentation in the top of the piston. The engine had serious loss of power.

Sounds like something may have gotten in the fan housing. Did ya leave any tool in there when you were getting ready for your trip?

That's what I would have figured. I checked that pelican artical before posting and those pictures are scary. I'll check the exhaust nuts and under the valve cover right now. Is there anyway to get into to the air ducts too?

About power it does drive fine, but when it's in that idle range when the noise starts the car bogs(like it's pulling something through the fan) and will stall if I don't give it gas.

Oh, also according to some peckerhead at the gas station it was making the noise before I shut it down( I had the radio turned up)

speaking of rod knocks, is it possible to have an "occasional" rod knock? i hear it usually when idling and at part throttle, but it goes away sometimes?! any ideas?

Matt, a knocking sound that goes away, especially after warm up, is an indication of a "loose" valve seat. The seat has not came out, but is a little loose when cold, and could tighten up when warm. Could also be an exhaust leak. I could be wrong, but I don't think a rod knock will go away.

i didn't think a rod knock would go away, but thats what it sounds like. a loose valve seat doesn't sound good. am i looking at some major repairs, new heads? or is this something that a competent machinist could take care of? my pop is an excellent machinist, and he could probably do any headwork i need for free.

I dropped seats in two engines. First one, no sound of impending doom - just wound it up and bam, the engine siezed. Second one sounded like a BB in a tin can. Came and went. Then one day it went. Drove another 150 miles home missing on one cylinder - trashed the head badly.

Your guess is as good as the others!

What he said. I think.

OOps! Hey Slits, the Datsun thing was mine. Just didn't know how to edit. Sorry.

what's the best way to take care of the valve seat before i drop it and completely
ruin my motor, assuming that the valve seat is the problem.

That pretty much nails how my engine sounded over about two weeks or so of daily driving. During this time, never did it knock on cold start. Drove to work/came home.
A slight knock at idle @ operating temp. No knock at cruise speeds. Then I stopped one day on the way home & when I started it up again (about 10mins later) it started right up & KNOCKED HARD (read SCARY!!!) knock on startup.
Teardown:#3 is smoked. I'll post pics comin' up.

now i'm starting to worry. i really dont want to have to do any major repairs when
i'm just now getting ready to get my 914 back on the road. i'd rather take care of this problem before i drop a seat. recommendations for repairs? should i plant on just rebuilding both of the heads to prevent this? what parts can i reuse if any? or should i just stick with all new parts as long as i'm doing a head rebuild?

Take the valve cover off and see if any of the valves have tightened up or see if one is really loose.

Other than that 1.) a leakdown test and 2.) Pull the suspect head

???????? What Datsun thingy?

Ooops, I spotted it.

after doing the valve inspection and finding the loose or tight valve, i'll then remove the head. when i'm looking at the head, what am i looking for? do i need to actually remove the suspect valve or valves to tell if it's ready to drop?

I've never caught one before it dropped - the seat will probably look different from the others as the seat is loose in the head. You could pull each valve and see if the seat drops out with it or have a auto machine shop inspect it. Sorry.....................

so is the valve seat part of the head or is it pressed in or something? does anyone here have experience rebuilding their 2.0 heads? just wondering how much i'll be able to do myself and how much a shop/my dad the machinist will need to do. i trust myself to put in springs and rockers and such, but obviously cant do machine work and stuff.

I was just wondering if a dropped valve seat sounds like?? Does it just sound like a loud valve?? I think my car might have a dropped valve because one of my valves is quite a bit louder tha the rest and i think it runs on three cylinders when the motor is really really cold but after it warms up it runs on all four cylinders. I have driven it like this for about 110 miles and it hasen't got any worse from when it started.

I think that's what it is too, it's very much like something is tying up the belt and pulling the eninge speed down.
I reached into the impeller fan, nothing, and looking inside the heater ducks, no luck.
What's the alternator thingy you mention and where would I find it?

well, i don't know if mine is going to drop the valve yet, but it sounds like slight rod knock or maybe some excessive valve noise: like a piece of metal slapping another piece of metal. don't know exactly what kind of exhaust is on my car, but it's pretty loud, and i can hear the slapping noise easily over my exhaust note. doesnt make the noise all the time though, at least not yet.

The seat is pressed in, but there are those that have "special" processes to do so. The heat the head and freeze the seat to get the tightess fit possible as the steel seat is pressed into aluminum.

Image one - seat is cocked - caught before it got loose in the combustion chamber:



Image two - seat completely came out and bounced around the combustion chamber for 150 miles (my head)



Image three - comparison of the non-dropped seat to the dropped seat - looking thru the intake port you could see light around the valve.

Less costly to check as you can see.

Does it stop making the noise when your engine is hot??

It came and went over a period of time. Even when driving, I would hear it and then it would go away. One day, it just didn't go away right after I overspun the engine in a spin. I could still do 100+ on 3 cylinders though

In the aftermath, at the shop, it sounded like a real bad rod knock.

thanks for the pics! seems like it's pretty easy to tell where the problem is once you get the head off. in the pic of the head that you caught before the seat actually dropped, it looks like it still damaged the head pretty well. is a head with that type of damage still good. would any good shop that does head work be able to repair this damage and install a new seat, or should i see a vw/porsche type shop?

That can be heliarced and milled back out. Most any aluminum head can be fixed - it's just a matter of money - the real bad one of mine is a paperweight now - if it were a race head I would spend the money and time to fix it - yes, I had access to a machine shop at one time and we fixed ones worse than mine - they were racing heads we had a lot of money into.

guess it's time to give my old man a call. he's been a machinist for most of his 60+ lifetime. i'd trust him to do the work before anyone else. and he'll do it for free! SCORE!!!

Here.... loose valve seat....

stststststtststststststststststststststststststststststststststst

Here.... minor exhaust leak...

ftftftftftftftftftftftftftftftftftfttftftftftftftftftftftf -fritter-

Here... valves need adjustment...

-hair comb being stroked from end on rev-

Here.... bent valve..

-radio edit-

M