#4 Cylinder intake valve stuck open |
|
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG.
This site is not affiliated with Porsche in any way. Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners. |
|
#4 Cylinder intake valve stuck open |
gnomefabtech |
Mar 19 2023, 09:20 PM
Post
#1
|
Member Group: Members Posts: 96 Joined: 27-December 22 From: Los Angeles Member No.: 27,063 Region Association: None |
So I'm trying to resurrect this 76 (or is it a 75?) that I just bought and it doesn't have compression on the #4 (rear right) cylinder. After some tests with compressed air it's clear that the intake valve isn't closing. I pulled the valve cover and the rockers move OK but that valve does not close all the way. Everything else looks good.
I have a lift but was wondering if I could pull that head without dropping the engine. It looks like there is room but I'm not sure about the engine tin etc. Seems like either the valve is bent or somehow stuck and maybe I can just fix the one thing there. Anyone pull heads while the engine is still in the car? |
VaccaRabite |
Mar 19 2023, 09:27 PM
Post
#2
|
En Garde! Group: Admin Posts: 13,426 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region |
Valve seat is probably dropped. You need to pull the head off. You can do it with the engine in the car but it’s not any fun. Don’t run the engine!
Top end rebuild time. Zach |
gnomefabtech |
Mar 19 2023, 09:37 PM
Post
#3
|
Member Group: Members Posts: 96 Joined: 27-December 22 From: Los Angeles Member No.: 27,063 Region Association: None |
Thanks for the reply. I'll pull off the intake and maybe be able to see if the seat is dropped. No idea if it ever ran in this condition. I never ran it.
Are dropped seats a common thing on these? The motor looks like it's never been opened and is totally stock. |
930cabman |
Mar 20 2023, 05:45 AM
Post
#4
|
Advanced Member Group: Members Posts: 3,000 Joined: 12-November 20 From: Buffalo Member No.: 24,877 Region Association: North East States |
Thanks for the reply. I'll pull off the intake and maybe be able to see if the seat is dropped. No idea if it ever ran in this condition. I never ran it. Are dropped seats a common thing on these? The motor looks like it's never been opened and is totally stock. Yes, the valve seats do fall out of their recesses with these aluminum heads. Being 1/2 century old, chances are the motor has been opened at some point. Drop the engine and remove the heads as a start. |
VaccaRabite |
Mar 20 2023, 06:03 AM
Post
#5
|
En Garde! Group: Admin Posts: 13,426 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region |
Thanks for the reply. I'll pull off the intake and maybe be able to see if the seat is dropped. No idea if it ever ran in this condition. I never ran it. Are dropped seats a common thing on these? The motor looks like it's never been opened and is totally stock. So, yes an no. I re-read your first post this morning with a non-sleepy head and there are some things we should confirm. You describe #4 as "Rear right." That would be Cylinder 3. #4 is passenger side forward - the one that is deep in the cooling tins. Cylinder 1 is Driver rear (shallow) Cylinder 2 is Driver Front (deep) Cylinder 3 is Passenger rear (shallow) Cylinder 4 is Passenger front (deep) For all the cylinders, the intake valve is the inside valve, and the exhaust valve is the outside valve (when viewing the cylinder bank as a paired set). Cylinder 3 exhaust the most common valve to fail, followed by cylinder 3 intake. This is because Cylinder 3 is the hottest of all the cylinders due to the airflow under the tins, and the exhaust valves run hotter then the intake valves as the intakes are getting cooled by fuel. I guess the first thing you should do is make sure the valve is not set super tight and the adjuster isn't holding the valve open. This may likely to be the problem, but it is easy to check, and you need to check valve clearance anyway. AND!!! A overly tight valve is often a sign of a failing valve seat. Or its possible whoever did the last valve check just really buggered up the job - but all things given I think that this is not likely. I'm also assuming that the engine spins free by hand. If you tested compression and the engine did not lock up or make very bad sounds, that's promising. Another indication that the seat is failing but has not failed. So the prognosis is better then it was last night when I was posting from bed, but still not great. But there is hope the last person to set valve clearance was just ham handed and got over tight. Obviously if the valve pops, it will lock up the engine, or damage the piston, or damage the rod, or all three. This is something you want to be SURE about before starting the engine. Zach |
Superhawk996 |
Mar 20 2023, 07:08 AM
Post
#6
|
914 Guru Group: Members Posts: 5,749 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
Drop the engine.
First - because that is the proper way to work on a 914 engine. Mid engine cars don’t lend themselves to doing work on the engine as installed. This is true of almost any mid-engine car. Second - almost all of these cars have been used and abused over the last 50 years. Gaskets and seals have dried out. Oil and gunk has clogged the oil coolers. Mice and rodents have been inside the engine cooling tin and have set up house or have left debris inside the tin. The reason that engines drop valves and valve seats is from being overheated. This can be due to build up of gunk on oil coolers and cooling blockages or engines that were run in a poor state of tune (lean and/or timing too advanced). The proper way to prevent this is to start by pulling the engine and making sure the cooling system is up to snuff. 2 of the 3 engines engines I’ve torn down had issues that would have led to serious overheating had they been run 1st before teardown & cleanup. Are you sure this isn’t your engine? Mouse house Blocked oil cooler - gunk and oil Blocked oil cooler on 911 engine Another very common issue on these engines is the number of people that have pulled the cooling flaps. Urban legend of the 80s was that removing the flaps would help prevent overheating. In fact, flap removal creates overheating because you loose the airflow through the oil cooler. These engines are not only air cooled, they are oil cooled. A bypassed oil cooler greatly increases the chance of overheating the engine. So drop the engine. It’ll be easier to work on and while it’s out you can properly inspect and clean it to ensure it cools properly. |
technicalninja |
Mar 20 2023, 09:23 AM
Post
#7
|
Senior Member Group: Members Posts: 1,154 Joined: 31-January 23 From: Granbury Texas Member No.: 27,135 Region Association: Southwest Region |
SuperHawk- that is BEYOND nasty.
Do people really remove the air flaps for the oil cooler? Drop dead stupid! I'm going to remote mount my oil cooler, remove the flap, and make another by hand to replace what I removed to force all the air through the fins. In the AC world the cleanliness of the heat exchangers is paramount. A system that looks like those engine picks would not work very well at all. I'm in agreement with everyone else- Check valve clearance first but if you don't know the history of the drive train removing it for inspection is a good idea. If it looks like SH's pictures you will save it from destroying itself. Those pictures are what I call a "time bomb"... |
TrailerParkBoy |
Mar 20 2023, 09:56 AM
Post
#8
|
Newbie Group: Members Posts: 8 Joined: 7-February 23 From: PNW Member No.: 27,145 Region Association: Pacific Northwest |
This is number four. A few weeks ago. Now doing full 2270 rebuild.
These were original 2.0 heads. Advice here was replacement, 50 years is past due! Attached thumbnail(s) |
brant |
Mar 20 2023, 10:11 AM
Post
#9
|
914 Wizard Group: Members Posts: 11,615 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains |
SuperHawk- that is BEYOND nasty. Do people really remove the air flaps for the oil cooler? Drop dead stupid! I'm going to remote mount my oil cooler, remove the flap, and make another by hand to replace what I removed to force all the air through the fins. In the AC world the cleanliness of the heat exchangers is paramount. A system that looks like those engine picks would not work very well at all. I'm in agreement with everyone else- Check valve clearance first but if you don't know the history of the drive train removing it for inspection is a good idea. If it looks like SH's pictures you will save it from destroying itself. Those pictures are what I call a "time bomb"... You don’t have to make a new flap For racing. We used to add two sheet metal screws to the stock flap to force full air through the cooler Be cautious to always pre warm the car and oil since you loose the warm up of a thermostat Not ideal for the street use As the stock thermostat design does work well |
gnomefabtech |
Mar 20 2023, 10:47 AM
Post
#10
|
Member Group: Members Posts: 96 Joined: 27-December 22 From: Los Angeles Member No.: 27,063 Region Association: None |
Thanks for all the input. I guess I'll drop the engine and see what's what in there. I have a really great shop with a lift and trans jack so I'm guessing I can drop the engine in an hour or so. It looks like it could use a new engine wiring harness as well because all the wires are very dried out.
The stock thermostat is still there but it's disconnected (of course). The rest of the car is COMPLETELY rust free.Check out this pic of the hell hole. I've never seen one that still had the original metal. |
930cabman |
Mar 20 2023, 11:14 AM
Post
#11
|
Advanced Member Group: Members Posts: 3,000 Joined: 12-November 20 From: Buffalo Member No.: 24,877 Region Association: North East States |
Thanks for the great shot of an original hell hole, I have never seen this before. Good information for putting one back together where who knows how the factory intended the seams, ...
BTW: (IMG:style_emoticons/default/welcome.png) |
ClayPerrine |
Mar 20 2023, 11:21 AM
Post
#12
|
Life's been good to me so far..... Group: Admin Posts: 15,416 Joined: 11-September 03 From: Hurst, TX. Member No.: 1,143 Region Association: NineFourteenerVille |
I know the original poster found his problem, but I wanted to add something that I saw on a 2.0 head.
The head was old enough that the valve seat started to recess into the head. Every time the valve closed, it hammered the seat deeper into the head. Eventually the valve stayed open. I readjusted the valve, thinking it was just too tight. It ran fine for about a week before the valve was too tight again. These are 50+ year old heads. At this point in time you are better off buying the new heads that are available rather than trying to use the ones you have. Just my $ .02. Clay |
gnomefabtech |
Mar 20 2023, 11:30 AM
Post
#13
|
Member Group: Members Posts: 96 Joined: 27-December 22 From: Los Angeles Member No.: 27,063 Region Association: None |
Thanks for the welcome. I'm a seasoned Porsche user, having owned a few tail draggers in the past, but am always ready to learn about the 914 stuff. This 75 just fell in my lap but I'll get it running at least and let someone else enjoy it's rust free glory.
My main project is a '73 that will have a "non Porsche" powerplant in it. I'll share that build once I have some more pieces in place. |
930cabman |
Mar 20 2023, 02:03 PM
Post
#14
|
Advanced Member Group: Members Posts: 3,000 Joined: 12-November 20 From: Buffalo Member No.: 24,877 Region Association: North East States |
I know the original poster found his problem, but I wanted to add something that I saw on a 2.0 head. The head was old enough that the valve seat started to recess into the head. Every time the valve closed, it hammered the seat deeper into the head. Eventually the valve stayed open. I readjusted the valve, thinking it was just too tight. It ran fine for about a week before the valve was too tight again. These are 50+ year old heads. At this point in time you are better off buying the new heads that are available rather than trying to use the ones you have. Just my $ .02. Clay Or a 1/2 century |
Shivers |
Mar 20 2023, 06:20 PM
Post
#15
|
Senior Member Group: Members Posts: 2,355 Joined: 19-October 20 From: La Quinta, CA Member No.: 24,781 Region Association: Southern California |
Thanks for all the input. I guess I'll drop the engine and see what's what in there. I have a really great shop with a lift and trans jack so I'm guessing I can drop the engine in an hour or so. It looks like it could use a new engine wiring harness as well because all the wires are very dried out. The stock thermostat is still there but it's disconnected (of course). The rest of the car is COMPLETELY rust free.Check out this pic of the hell hole. I've never seen one that still had the original metal. Nice. I was surprised too after seeing the battery tray, and cutting it and the metal behind it out. The HH looked really good, below it too. |
gnomefabtech |
Mar 20 2023, 07:21 PM
Post
#16
|
Member Group: Members Posts: 96 Joined: 27-December 22 From: Los Angeles Member No.: 27,063 Region Association: None |
I guess fortune smiles upon some of us! Did you cut out the battery tray to replace it?
|
Shivers |
Mar 20 2023, 11:22 PM
Post
#17
|
Senior Member Group: Members Posts: 2,355 Joined: 19-October 20 From: La Quinta, CA Member No.: 24,781 Region Association: Southern California |
|
robmac571 |
May 10 2023, 12:42 PM
Post
#18
|
Newbie Group: Members Posts: 1 Joined: 23-January 21 From: Seattle, WA Member No.: 25,114 Region Association: Pacific Northwest |
This is number four. A few weeks ago. Now doing full 2270 rebuild. These were original 2.0 heads. Advice here was replacement, 50 years is past due! @TrailerParkBoy who are you going to for your rebuild? I'm also in need of top end rebuild and am in the PNW. |
Lo-Fi Version | Time is now: 27th April 2024 - 10:47 AM |
All rights reserved 914World.com © since 2002 |
914World.com is the fastest growing online 914 community! We have it all, classifieds, events, forums, vendors, parts, autocross, racing, technical articles, events calendar, newsletter, restoration, gallery, archives, history and more for your Porsche 914 ... |