Like 31Vicky said,,remove rockers and apply air to the plug hole. I always air test every valve job that I have done. At least that way you know that all the valves are sealing to the seats. If you have done 100 head gasket changes in the past,,I can't imagine that you could screw it up so bad to have zero compression. I bet on the rockers not closing because of clearance,,,or some problem like that. Good luck. Tommy
Oops,,just reread the original post,,,it says Rebuilt head. Does that mean it is a head that you purchased and have no history on? That might open a whole nuther can o worms. Really good luck now,,hope it works for you. Tommy
Put motor on tdc with rocker arms in place and air comes out the intake. Loosened rockers took all pressure off of the springs and air still comes out intake. I did not check the timing chain itself, but the harmonic balancer timing marks line up with tdc, and the intake valve is at its closed position. I bought the head used rebuilt, but I think I can talk to the machine shop. I think I might have bent valves that are not closing, or I I don't even know. I probably have only done 30 or 40 head jobs, but I don't think it should be this hard. Thanks for everyones input. Keep with the ideas, I will keep checking things. I still think the head is coming back off. With a long 1/2 drive Snapon ratchet on the crank, it turns over pretty easy.
So you think there's a bent valve on each cylinder ? All 6 have zero compression and nothing was done to cam or timing chain & all cylinders had 135 plus compression before removing the head.
No, a bent valve on each cyl. does no make sense. I know I am missing something, but what. If the timing marks were not on, but they are, I would be leaning towards timing chain jumping. I took the head off and put this one on.
Ok, how ? Based on what you said : You drive it into the garage Had 135 plus compression on all 6 Did no cam or chain work. I doubt this is one of the worlds greatest mysteries. It's not a mythical or mystical problem, its mechanical. When mysticism plays a part , its the mechanics methods. Go back over your work. TDC marks line up twice on a cycle so there's a 50% chance you were TDC overlap instead of TDC compression. Removing the rockers completely eliminates the valve train components and cam timing. If you have them off means OFF and put air into the cylinder that will tell you what's up with the valves. You could have a bent one in each cylinder but it seems unlikely. Maybe the seller / rebuilder is a goof***. Take you 30 mins tops to find out.
I doubt this is one of the worlds greatest mysteries. It's not a mythical or mystical problem, its mechanical. When mysticism plays a part , its the mechanics methods. This should be a quote^^^^^^^^^^^^^^^^^^^^ I will double check my work and report back. I agree on the mechanical part, that's why I say it shouldn't be this hard. I also do not think the timing chain jumped. Thanks
Those shims are to manipulate seat pressure, or for clearance, or to make up for cut valve seats and ground valve - possibly all the above. It's been at least 30 mins. You should have removed the rockers and applied air to all cylinders by now and have a definitive conclusion on the valves leaking or not.
When you take the head off turn it upside down and fill each valve pocket with something like Kerosene and see if it leaks through the seated valves. It should maybe let a little through, but from what you are describing you have a major non seating issue. Tell us more about the "rebuilt" head you have. I just took a set of World Product sbc heads to the machine shop for freshening up and they had only break in time on them. The machinist called me and said they needed a complete valve job because the valves were not centering exactly in their seats. I know this machinist well, so he was not pulling one over on me. It is very possible whoever did your valve job did something wrong. Don
Went back to check my work. I am trying to get a leak down tester, but do not have one yet. I checked this 2 ways first, with the piston up and valve closed, and spring pressure. Then with no spring pressure. Cyl. 1-3 seem to have more air leak than 4-6. 1 having the most with 6 having the least. When I started out it was on 1 at tdc then I rotated the crank 360 degree, and went to #5 which is next in the firing order, but it was no where near the mark on the crank when 5 was at tdc.
Head has to come back off and examined to see what is going on. My guess is you have a bad valve job. What is the history on this "rebuilt" head ? You keep avoiding that question. Don
All common 4 cycle engines fire all cylinders in 720 degrees of crank rotation. Since your engine is a 6 cylinder, it fires every 120 degrees (720 divided by 6 = 120). If you started on #1 and wanted to bring up the next cylinder in the firing order (#5),you would only rotate the crank 120 degrees, not 360 degrees. That would have brought the fourth cylinder in the firing order to TDC and the valves would have been open on #5 giving the results you got.
I agree. A local salvage yard bought a Jeep with a bad motor but, had a head that just got rebuilt by a local machine shop. I could tell a exhaust valve had been marks on it. The head was clean, and said to be magnaflux checked, that came back good. That is what I know about it, until I talk to the shop today.
You need to know how much the head was decked. AND simply add a shim under each rocker stand that same dimension. Also if the new head gasket is thicker or thinner than the old one, figure that into the math. NO NEED to take the head off.!!!!!!!!
Even if you had a timing chain jump time, you would still have compression in some cylinders, not zero in all cylinders
Ok, now things are starting to make sense. What you have is a junkyard head that they told you was rebuilt, not a head that you personally had done. Pull that head and take it to someone who knows how to do a valve job and ask them to check the previous job (if there WAS even a previous valve job). To complicate things more, the engine this head came off of was junk.......that should tell you something. This ain't rocket science, it ran when you drove it into the garage, all you did was pull and replace the head, now it doesn't have compression. The head is your problem. Don
Suggestions about the engine having "jumped time" is, IMO, a complete red herring in this case. The OP stated the engine ran more or less fine before the head was changed. He also states the timing gears/chain were not worked on. Would an engine with jumped time exhibit compression problems? Yes, of course it would. But that is not the same as it actually having done so. The probability of the engine spontaneously jumping time is about the same as winning the Powerball Lottery! If this were an overhead CAM engine, then questions about valve timing would be more relevant as the timing would have been directly involved in the head replacement. Not the case here.
Ok, restart on this thread- i have no compression. i purchased a head from a junkyard, they said it was rebuilt. I installed it just like I did the last 100 or so heads that I've done. Prior to this work , This car drove into the garage, had 135 plus compression on all cylinders, I did no cam or timing chain work. All we have to go by is what you tell us. Leave out 1/2 the info and you can only get 1/2 ***ed pseudo correct answers. Sometimes these threads go on for pages with the most obscure ******** guys can think of. Junk yards tell stories. This head is rebuilt is the same as the check is in the mail. Take your original head and the junkyard head to a machine shop or back to the boneyard. Pretend it didnt happen yet and start over. Anyone else wonder why the head came off in the first place?
^^^^ Absolutely. Timing was not disturbed if he did just a head removal/replacement. His problem is that he took the junkyards word that a head on a trashed engine was rebuilt (we've all done similar things), but this time it bit him. That was the problem with the World Product heads I just had done. Brand new heads, break in time only, but then the car sat outside with the valves open for 4 years. Don
You are ***uming that the herring ******s actually read something, formed what seems like a reasonable opinion, and shared it. It's one of two things, they have no knowledge and should be watching cartoons or didnt read a ****ing thing .
Just a thought!( My one for the day) If the head was rebuilt,could lapping compound(If they did it and not clean it off) keep the valves from closing all the way? Pete
Even if valves are not 100% seated when closed, there should be some compression. Zero would mean big hole somewhere-in piston, no rings, no head gasket, hole in head etc... A leakdown test will determing where the loss is.
We can keep beating our heads against this one but until he pulls the head and has it checked by a competent machinist we are just throwing darts at a board. He started with an ***umption that the head was good and until he confirms it is or isn't he is just spinning his wheels. Time for him to put down the keyboard and pick up some wrenches. Don
Leak down or a simpler old spark plug with air fitting braised onto it. 90% of compression testers look like this and its really easy to get air into the cylinders. With zero compression a quote "leak down" un quote tester is of no value, except for the fitting. 30 mins tops. With the head off, testing valve sealing becomes difficult for him, and gravity based liquid isn't very conclusive.
If you get TDC turning to right, the way engine turns. 1 back off intake should be closed now go to tdc valve should start to open. 2 turn right to tdc one full turn ,Both valvels should be closed 3 now turn 180 dges to bottom, then the exhasust valve should start to open. You may have tiiming chain probelms. You must of had problems why did you change the head.
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