techboy Posted July 25, 2011 Report Share Posted July 25, 2011 (edited) So I just discovered recently that my car has a mechanical head. I'm still trying to get this thing to run right, I got tired of testing sensors, wires, and swapping TPS's, so I popped off the VC ... turns out it's mechanical and the valves were way too tight. So, I loosed things back up into spec via the FSM w/ feeler gauges and the car definitely runs and idles much better, but alas ... still stumbles and stalls below 3K. Here comes my question ... I was doing some searching on here and it looks like the mechanical heads came from Caravans and I read something about the valves needing to be replaced w/ TURBO valves. Am I understanding correctly and, assuming some uninformed P/O just dropped this thing on here w/out swapping valves would that cause the symptoms I'm having? Edited July 25, 2011 by techboy Link to comment Share on other sites More sharing options...
Dad Posted July 25, 2011 Report Share Posted July 25, 2011 (edited) Turbo engine came with stellite faced exhaust valves. At this point I don't think you need to worry, just get it running good then later if you ever remove the head you can install the correct valves. Dad Edited July 25, 2011 by Dad Link to comment Share on other sites More sharing options...
vbrad511 Posted July 25, 2011 Report Share Posted July 25, 2011 Don't worry about the head. My 88's doesn't have hydraulics. I've got another head in the garage with mechanicals too. I've parted a handful of SQ's and their motors. Most had hydraulics, some didn't. Link to comment Share on other sites More sharing options...
techboy Posted July 25, 2011 Author Report Share Posted July 25, 2011 (edited) I'm not worried about the head per say ... I see from my research a lot of guys swap over to them. I was just wondering if maybe the head wasn't properly set up for a SQ by a P/O if that was my problem. I'm gathering from what you guys are saying though, that's not the case ... I still have some other issue. Edited July 25, 2011 by techboy Link to comment Share on other sites More sharing options...
vbrad511 Posted July 25, 2011 Report Share Posted July 25, 2011 Have you done a compression test? What were the numbers? Link to comment Share on other sites More sharing options...
Indiana Posted July 25, 2011 Report Share Posted July 25, 2011 The heads are all the same, the cams have the same specs just one is slightly different lift because hydraulic lifters end up with zero lash,the springs in late models were the same. You'll not know it if you have non turbo exhaust valves. There were no more mechanical heads after 1984, the lifters came out with the 85 model year engines. Replacement heads were less money if they were mechanical. Caravans always had jet valves, ALWAYS. If you have a non jet head the casting is the same it just didn't have a hole drilled in it for the valve to go in but the intake flange passages are ALWAYS there with the exceptionon the 90s model AU Magna heads with the large rear water port since that is only a fwd head. The same thin area between the intake and exhaust valve cracks on all of them including Magna heads. There were more non jet heads used, they all crack that has nothing to do with it. Internet BS wants you to think jet valves cause cracks and Caravans were non jet, both are wrong. What lash did you have? Are there jet valves? Link to comment Share on other sites More sharing options...
techboy Posted July 25, 2011 Author Report Share Posted July 25, 2011 (edited) What lash did you have? Are there jet valves? There are jet valves ... so it must be a caravan head. They are disconnected, but they are still in there. Not sure about the lashes. And yes, I've done a compression test. Shows about 90 across all 4 cylinders. The FSM calls for 97, so it's a touch low. I wanted to rebuild the motor this spring, but I wanted to get it running right first, it's taking me so long to figure this thing out I'm way behind schedule ... Edited July 25, 2011 by techboy Link to comment Share on other sites More sharing options...
Komeuppance Posted July 25, 2011 Report Share Posted July 25, 2011 I don't think it's going to run very well at 90psi. You sure your gauge is accurate?? -Robert Link to comment Share on other sites More sharing options...
Indiana Posted July 25, 2011 Report Share Posted July 25, 2011 Lash, that's the gap under the screws. What is yours set at? You got a good battery in there. Link to comment Share on other sites More sharing options...
Starfighterpilot Posted July 25, 2011 Report Share Posted July 25, 2011 (edited) Did you have a foot, brick or something similiar, holding the accelerator pedal all the way down, causing the throttle plate to be wide open, when you were doing the compression testing? If not, the TB throttle plate is almost closed and this will give you lower compression pressure readings. Were all of the spark plugs out when you took the compression pressures? If not that will also give lower pressures too. You probably know this, but I'm just throwing this out there for the new guys. Have you tested your CTS, done a TPS/ISC reset yet? Do you have any error codes? For What It's Worth. KEN Edited July 25, 2011 by Starfighterpilot Link to comment Share on other sites More sharing options...
vbrad511 Posted July 25, 2011 Report Share Posted July 25, 2011 There are jet valves ... so it must be a caravan head. They are disconnected, but they are still in there. Not sure about the lashes. And yes, I've done a compression test. Shows about 90 across all 4 cylinders. The FSM calls for 97, so it's a touch low. I wanted to rebuild the motor this spring, but I wanted to get it running right first, it's taking me so long to figure this thing out I'm way behind schedule. Not neccessarily true. All of my heads, hydraulic nd mchanical have had jet valves, and they've all come off SQ's. My 88's got between 90 and 95 in each hole too. It runs just fine, but maybe not quite as much power as one pushing 120. Link to comment Share on other sites More sharing options...
techboy Posted July 25, 2011 Author Report Share Posted July 25, 2011 Ok, let's back up a minute before I address the other questions asked since my last post. This is going to sound real basic, but what is the compression supposed to be on these motors? I have an 88 car and an 89 FSM. My 89 FSM says on page 9-5 that Compression pressure should be 97psi. I clicked on the compression test link in the FAQ and it says standard value is 142 (http://www.starquestclub.com/forum/index.php?showtopic=28020). I clicked on the on-line 88 FSM and looked at the coresponding page to the 89 and it's not listed. So ... what is the official compression supposed to be? I compression tested mine when I changed my plugs about 2 months ago just for kicks and got 90 across all 4 cylinders. Car runs great above 3k. It just stumbles and chokes when you try to accelerate and won't stay running at idle. It's been like that since I bought it and drove it home. I've replaced just about every sensor and rebuilt my TB, installed working OEM injectors. You can see this thread to see all I've replaced. (http://www.starquestclub.com/forum/index.php?showtopic=121297&st=20) Top of page 2, post #22. Link to comment Share on other sites More sharing options...
Indiana Posted July 25, 2011 Report Share Posted July 25, 2011 It matters that they are consistent. I've seen 175psi on them. I've seen about 90 it depends on many things. We do not as a whole have 100% stock cars to give an answer of 20+ year old engines compression. Usually if your gauge is the same as the next guys you'll have 110-125. You could have hydraulic lifters with air and trash in them and end up with 92, 78, 101, 64 and someone will say you have a blown headgasket and you won't. Link to comment Share on other sites More sharing options...
techboy Posted July 25, 2011 Author Report Share Posted July 25, 2011 Ok, so then according to Indiana and vbrad 90 is not outside the scope of reason. Link to comment Share on other sites More sharing options...
StarquestRescue Posted July 26, 2011 Report Share Posted July 26, 2011 A leak down test will tell the tail. A lot cheaper than doing a full rebuild when all you may need is a head job, or to to replace bad jet valves. try another compression gauge. 90 is way low on my gauge. Maybe some one put a " hot cam" in it, those some times effect compression. as well as make mostly stock on tuned cars run like crap. If you valves were not closing the whole way you could have burn valves. I would expect uneven compression though. A leak down test can tell a lot. Goggle is your friend. When you say they were to tight, what does that mean? Zero lash? .005? Link to comment Share on other sites More sharing options...
techboy Posted July 26, 2011 Author Report Share Posted July 26, 2011 When you say they were to tight, what does that mean? Zero lash? .005? If I remember the numbers correctly I think they were like .003 and we loosened them up to .010 and noticed right away that the car ran alot better and there was a little bit of a valve tap, which it didn't have before. Link to comment Share on other sites More sharing options...
Indiana Posted July 26, 2011 Report Share Posted July 26, 2011 All I run on mechanical rockers is .003" You could have carbon from burning oil, leaking valve seals that restricts air flow that is all around the valve stem, the seat and both sides of the valve. Get two cans Mopar Combustion Chamber Cleaner from the parts Dept. at your local dealer, that dissolves carbon and can loosen up stuck rings that are binding in carbon. Link to comment Share on other sites More sharing options...
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