I have a Ď12 that has run great for many years. Z head but otherwise pretty run of the mill. I blew a head gasket so I replaced it with another copper one and now it wonít start unless towed. Did a compression check and itís 25 psi on all
Of the cylinders. I took the head off to look for som thing strange and nothing seems odd. All valves are working nicely.
I put starting fluid in carb and nothing when I crank. Almost like itís not sucking the fuel up. I have hot spark at each cylinder.
I donít know how I go from good running car to DOA by replacing a head gasket. Need some advice
When you blew the head gasket, did you cook the engine? running to hot can collapse the rings.
25 psi is a little low, did you check the head to make sure it wasn't warped ?
Try a couple ounces of oil in each hole and crank it through, then see if compression goes up. Indicating ring problems.
Flooding can wash the rings off and create a poor seal also.
I don't think I cooked the engine. Still Drained plenty of water out of the system when I changed it. Its a good thought though. I put RED RTV on the head gasket this time around to make sure of a good seal.
Before this the last time I checked I was a lot higher for compression.
I'll try the oil in each. Thats a good test.
keep the ideas coming!
Do not use rtv on the head gasket.
I agree with Shane. RTV can ooze out enough to get under the valves and/or block water ports.
Copper spray sealer is the only thing I put on a copper gasket.
Are you sure the head gasket blew? Could timing gear have skipped a couple of teeth and killed the compression, and still be bad?
John, one more question please.
Did you do a compression test before and after installing the Z Head?
The 25 psi suggest you either have a bad gauge or the adjacent cylinders are dividing the pressure.
Then too, 25 psi will not be enough to suck in enough gas mixture to make a good bang.
Years ago, I had a Ford engine so worn, that if left for a week or two, it would not start until I added a little oil to a cylinder or two to increase the compression enough to suck in some fuel.
Once a few cylinders fired, the engine turned fast enough to splash some oil on the other cylinder walls and raise the compression enough to bring gas into all the cylinders.
Normal compression readings for a good stock engine are usually 50 to 60 psi and an engine with 40 to 45 will still run well with less power.
The Z Head should raise that number to almost double what it was or at 80 to 90 psi at least.
The compression has to be measured with all 4 spark plugs removed to make the engine turn faster and easier.
It was definitely a head gasket blown. The car looked like pig pen in Charlie Brown only with white amoke
Here is a video of it
The compression the last time I checked was 55+. Donít remember the exact number. I think I will try a stock head I have here to rule out the head being warped, then goto some new rings.
Iíll give the cylinders a nice light honing to get a good seat. There is no banging or anything but itís worth a go at it.
If there are more ideas keep them coming !
You need to do a leak-down test. This will tell you everything you need to know.
Honing without replacing the rings would not be a good thing, and unless your bores are perfect, you'd likely need to fit oversize rings and file to fit. Lots of work that is not warranted at this juncture. Do not start adding variables to your compression issue until you understand it's genesis.
I changed the head gasket earlier this summer due to a leak between the last two cylinders. Lots of scraping the gasket surface clean and some of the scraped gunk and soot may have slipped in between the open valves and their seats. I cranked the engine to get access to scrape all pistons, so all the valves were open at some time during the process and I was in a bit of a hurry to be able to drive the next day, so I didn't blow it all through with compressed air before bolting it together. Naturally I didn't get enough compression when trying to crank start the engine after the repair, but I realized what was the problem, and since the engine is an air pump, all it needed was more cranking speed than I could make with the crank to blow it clean - I had to ask my wife to pull start my primitive pickup with the modern (shrug..)
It worked like a charm, started in a few yards and when I came back from the test drive it had normal compression, so I could hand start it as normal. Since I have an aluminum Prus head I waited until it was cold until I retorqued the head. A cast iron head can be retorqued hot.
It's been suggested above and seemingly ignored: DO A WET COMP TEST ! It will tell you if the rings are the problem BEFORE you do work you don't need to do. What was the head gasket symptom that caused you to change it? Cannot see a head gask replacement causing 25 Lbs across the board on it's own even if you didn't clean the head bolt holes out. Something else is going on.
Thanks for the heads up on the Wet compression test. I am assuming that is oil in the cylinders and then a compression test.
The reason I changed the head gasket is shown above in the short youtube video.
The something else going on is the good part and challenge.
I think you'll have to take the head back off and replace the headgasket with one that doesnt have curdled RTV on it!
A light tack coat of copper spray is all you need on the replacement gasket (if any).
Make sure the deck of the block is spotlessly clean and chase out the headbolt threads down to the bottom of their bores. Torque the head bolts evenly from the center out to the ends and go!
I agree with Dale.
Watched the video. White smoke? Did you have anti freeze in the radiator? Really there's not much there in what 10 seconds? Please explain what was happening because that video is zip in my book.
I assume that your car doesn't have a starter. It could be that when you are checking the timing, you are not cranking fast enough. Before you give up and pull the head, try a few drops of gas in each cylinder and see if it will start for a few seconds. Or if you have access to starting fluid, spray a little into the carburetor while the engine is being cranked. You could have a lack of fuel to the carburetor. What I am going to say next doesn't mean you are stupid! But have you checked to be sure there is gas in the tank and that the valve is on? Do these checks before you pull the head.
If you pull the head,while you have the head off, check the valve opening and closing. Intake opens with piston down 1/16" after top dead center. Intake closes up 9/16" after bottom dead center. Exhaust opens with piston up 5/16" before bottom dead center and exhaust closes with piston at top dead center.
Each cylinder should be the same. If all valves are too late or too early, your timing is off.
Compression is low. Several things can cause low compression: Leaking rings as others have suggested, leaking valves, cam shaft slipped timing, head casket leaking, too low rpm while testing compression, warped head, block surface not flat or has low spots, incorrect torque or wrong torque sequence or not re-torquing, head bolts bottoming out or too much friction. Fix the low compression first. Use the copper seal as others have suggested. Bottom tap head bolt threads in block and check height when bolts are bottomed out. Use thin stainless washers under the heads of the bolts.
If the car runs after being towed, as you have reported, then there is nothing wrong with the fuel or ignition.
Something caused the head gasket to blow. Check the head for warps or other damage. Try switching to a Ford head that is in good shape.
Did you remember to have the throttle wide open during the compression test? A closed throttle will give a false low reading.
I wonder if that gasket sealer might have gotten into the rings causing them to stick? The thing which puzzles me is the same low compression on all cylinders. How high altitude do you live? Compression does tend to go down at higher altitudes, but not that much.
John : while I realise all these guys are trying to be helpful in the real mechanical repair world you don't shoot from the hip, guess and take a chance mainly because it costs money. You need to take this one logical step at a time. #1 Please describe in as much detail as possible the symptoms that lead to the head to the gasket change because your video shows practically nothing. #2 DO THE WET COMP TEST BEFORE YOU DO ANY MORE WRENCHING !! Please report when possible.
assuming you did a proper dry test;
1 remove all spark plugs
2 open throttle & choke fully (IMPORTANT)
3 Squirt a few shots of engine oil into 1 cylinder
4 hook up the gauge & crank at least 7 complete
5 take a reading & write it down
6 do the other 3 cyls the same way
A rise in pressure generally indicates worn
One more thing; 25 is low but if the weather is mild where you live it actually should start.
At the suggestion of a member off line I hooked up to compressed air to each plug hole to test where the leak is. I made the hookup and did an initial test and found it is leaking past the rings. Iíll continue testing tomorrow to make surety initamfinsimgs are correct but now Iím in to something.
When itís back together Iíll put a new head on it just in case with a copper head gasket and spray on sealant.
Thanks for all the input along the way!
I would still put some oil in the cylinders and retest it.
Rings don't seal well if they get dried out, for whatever reason...gas, water, brake clean.
I've had injectors leak on modern engines and they'll wash the cylinder out and show near 0 psi compression.
I would still put some oil in the cylinders and retest it.
Rings don't seal well if they get dried out, for whatever reason...gas, water, brake clean.
I've had injectors leak on modern engines and they'll wash the cylinder out and show near 0 psi compression, till you put some oil in the hole.
John, just out of curiosity, how did you determine that air was escaping past the rings by doing this test?
Your test means absolutely nothing. Air will leak past the rings in a cold engine. Doesn't mean a thing & proves nothing.
a leak down test can tell plenty
DO NOT PUT RTV ON HEAD GASKETS!!!
Copper spray or nothing.....
If it is a new head gasket, just clean it and reuse. Chances are as it has not been run, it was only taken to torque once. I don't see the reason or need to replace it at this point unless you want to spend $.
The problem with a leak down test is there will always be leakage. The rings, especially when cold, will always leak. You will always hear air from the breather/filler. It can show leaky valves. True. but a wet comp test will show that too and indicate true ring condition to boot. His test shows/proves nothing.
Thanks for all the information and opinions. There is a lot of knowledge on this forum and it proves once again that when we all put our heads together we have a lot of ideas. The fun part of the hobby is this collaboration. I am trying all the ideas. Its just fun......
As for RTV I have been running it on my T's since I was 16 years old, I'm now 48 years old. Many thousands of miles driven in this configuration and this is the first head gasket issue. Some may not believe in it, however I do. Oh Well. Its just my humble experience.....
OK. Don't tell us what's going on. Your choice. But if you're really looking for help...Ö..
I agree with you, and I'm not picking on you with this post. It is meant in the best spirit for perhaps other folks who don't know what a leak down test is.
It isn't simply pressurizing a cylinder and "listening". It is a test that compares pressure applied, to pressure retained, in the cylinder. Yes, the rings will leak...no doubt of that. However, it is a "percentage" value between the two readings and gives a comparative health picture each cylinder. If you do in fact hear leaking from the carb or exhaust, that is a bonus for your diagnosis.
Seriously, all of you who are sure you know what a "leak down test" is, please read one of the two links I provided, and then decide for yourselves if you really understood it before reading.
John- I carefully re-read your original post and I think you incorrectly assumed that the head gasket failed because of the smoke and after replacement you still have a problem. 25 PSI is unacceptable.
Have you checked your timing gear? Is it fiber? You can see the cam gear through the oil fill hole. A failed timing gear can cause what you are describing.
When an engine fails we all want to believe it's going to be a quick an easy fix and often times the real problem is overlooked.
...PS- no head gasket in the history of mankind is going to need RTV applied to it.
Show me the specs for a T engine involving a leak down test & how you determine the percentages of leakage for the T. Without untold mileage/wear on it to boot. He's just guessing. He hears air from the breather so the rings are bad. Wrong. Just plain wrong. A leak down test probably has it's place but it's not here. What he's done proves nothing & tells him nothing. I'm with Tim. Just didn't want to be the first to say it. The head gasket business might have been a mistake from the get-go. Mis diagnosed.
I have to add my 2 cents, while not a rebuilder , i have worked on engines for a while, and as for as sealant on the head gasket, you should not need any. I was always told that white smoke shows a coolant leak, usually from a crack in the blocked or in your case , a bad gasket, possibly from over heating the engine. check the head and deck to make sure they are not warped and are flat and look for any cracks in the water jackets or valve seats. Also, oil in the cylinders will show worn rings. Pressure in the cylinders will leak past the the ring gaps when dry. this is just from my past experience
Charlie, there is no "T Spec" for a leak down test...it is the same for any internal combustion engine. Since you apparently don't know what a leak down test is, nor took the time to read what it is, here is the test.
Percentage leak down:
for example, 80PSI retained divided by 90PSI entering, equals 11% leak down (89% retention).
Since you asked, there, I showed you. And if ever there was a time to do it, yes, it's here.
Sure, the timing gear may be torn up, but just because someone does not know how a test is performed nor what it means, does not mean it is not a valid, non-invasive test that WILL indicate a diagnosis.
I've seen it done twice and read both the posts & I'll repeat: what will it show him that a wet comp test won't? The wet test will show valve & ring condition when done with a dry test plus requires nothing more than a decent comp gauge some oil and a pencil & paper. Positive results no guessing.
A compression tester only give what it gives. If timing is out, the dry or wet test will only give what the valves let in (or out). Very low compression test could be many things. A leak down test might show GREAT compression and point directly to timing/cam gear.
Scott, being a mechanic(auto,42 years) and having owned an airplane for 36, I am aware of how a pressure leak down test is performed. The really important thing is to immobilize the crankshaft before doing it! The piston has to be in the TDC position so the valves are closed, then the crank is held, to keep the piston at TDC, and air is applied through a measured oriface, with inlet pressure gauge and retained pressure on the other. Now, on an airplane, it is reasonably simple to hold the prop by the tip, and keep it from moving (having seen what it can do if left un held), but holding a T crankshaft may be a wee bit harder. The only way I can see, is to bring it ALMOST to TDC, and leave the hand crank engaged and put something strong under it to hold it, since the T hand crank doesn't begin to have the leverage of a propellor. Airplanes use 80 psi in and have to hold usually 60 psi, on a warm engine.
If you look above, I was the first to mention timing gear. Bill
"Warm engine". The 2 I witnessed done this way.
By the way it's done warm because cold the leakage thru the rings worn or not would be ridiculous.
Lesson really over.
you are of course absolutely right. That sucker could get away from you if precautions are not taken, and that's timely advice that I should have included. Thank you. With handbrake set and low and reverse bands braced/depressed and caution used, it's possible.
Just curious to see if the problem has been found? Hope so!
I continue to work on it quietly and I have been contacting people off the public forum. I received a lot of good advice here but it turned into a bit of a lively discussion and I did not want to feed into it anymore.
I have it pretty much narrowed down to the rings and I am currently preparing a replacement engine to go in the car. The bore is .060" over and to do the job right it needs to go out to a rebuilder. I also wanted to put a starter on it due to shoulder issues as well as getting it balanced. I figure this rebuild will take me through the next 20-30 years.
The engine has earned some more attention from me other then a quick fix, so it will be getting a mini makeover this winter. In the meantime I will be putting a Rajo BB Equipped engine in the car and I can take my time with the rebuild. Come next winter the rebuilt engine will be ready to go in and off we go...
Only sealant i used on a head gasket is copper coat i prefer spray version
Next time heads off check valve timing weak valve springs or atleast time to grind them
Low 25psi in each hole leads me to supect timing