could anybody help, i have a 1983 he v12 xjs and have recently replaced both the cylinder heads, Have had the engine back together and had the engine running, Carried out a compression test on all the cylinder, am getting about 160 - 180 lb on all cylinders except 6b which has no compression what so ever any suggestions.

 

You probably don't want hear this but off with the head again.

Were the heads new or reconditioned, if not you may have a valve that is not sealing. Which ever way I think it is off with the head - so to speak...

 

Just a silly thought but you didn't do the valves and then just use the original shims did you?
I would be checking my settings.

 

I agree.

Since the heads were off recently, and obviously valve work carried out, I also ask what tappet clearances you set the valves at?.

This setting is time consuming at best.

I would off with the LH tappet cover, and check, very carefully, the tappet clearances you have at this point in time. It may be a closed up clearance, as in absolute zero, which would require the camshaft off, and that would mean messing with that very expensive timing chain tentioner.

A dropped valve seat after head work is NOT common, but not impossible, if done wrong by the machine shop. Also a dropped seat usually has a lot of clattering going on.

The fact you are not mentioning any "blow back" thru the inlet, it will be an exhaust valve giving the grief.

 

A mighty thank you for the help. Have carried out the compression test on the 6b cylinder having done nothing to the car since. Am now getting about 140 -150 lb pressure. However am going to check all the valve clearances again. Prior to removel of the head i was gettin 110 - 120 lb from each cylinder, to an improvement indead and all test were carried out with a cold engine.
Have other issues with leaking sandwich plate and leaking timing cover plate, only apparant after cleaning the gunk off the front of the engine, sods law.

 

OK, good so far.

Be VERY careful with that oil leak diagnosis. I have seen many a V12 dismantled for the same oil leaks when all the issue were the following, in NO particular order:

D rubbers at the rear of each cylinder head.

The camcover gaskets can/do leak, but the later "Gortex" type are oil tight.

The vent elbow bolts on the front of the LH cylinder. These bolts require a copper washer under the heads to stop the weeping/leaking.

The oil filter housing drain back nonsense o/rings. PITA to get at, but they do leak.

The 2 small 6mm hoses on the "walking stick" oil relief valve drain out. Also in the oil filter housing area.

The "special" rubber plug in the RH side face of the timing cover that is the access for the locking ratchet of the timing chain tentioner.

The o/rings on the elbow for the oil cooler return pipe at the front of that sandwich plate, a very common oil leak area. Some markets do NOT have that elbow, we Aussies DO, as we got the "poverty pack" by pass oil cooler set up.

The "tin pan" sump itself does leak where it attaches to the sandwich plate.

When I did all ours, I used NO gaskets on the sandwich plate, or tin pan. Just Hi-Temp Red RTV, done as directed, and timed as directed. NO leaks ever.

 

thats what i use Red RTV, just about everyplace , except head gaskets!

 

Thanks again but the car is in remarkable good condition. It has only covered 145K km from new with the paperwork to back it up. The bloke is remarkably clean and dry except for the oil leak at the front drivers side of the block, Have removed the air pump and the alternator bracket, cleaned up the timing cover plate, sandwich plate and block then left over night, Oil is slowly seeping out. If i could get some red RTV in the gap that will resolve the issue. .I have a new sump gasket to have fitted which i know is leaking and have already changed the GM400 sump gasket which was also leaking slowly. Will recheck the valve clearance this weekend time and wather permitting.

 

i used RTV on the pan(SUMP) to sandwich plate also,no gasket, seems any gasket i have used that is paper or cork always seeped oil thru it, like a wick thing.

also rtv on bolts seen em leak there also!

mine leaked all the places that Grant mentioned!

only ones now is crankshaft rear rope seal, and very slight sandwich to block, and that is a lot of work to repair!

so i'm leaving them be , like a typical normal jag V12 pre-he.

 

well as promised i have checked the valve clearance, Yes i did reuse the original shims for good reason, they are all with in tolerences smallest gap is .011 and the largest gap is .014, am aware they should be within .012 - .014 so am very please. Am now putting the engine back together and will try to get the engine to idel below 1700 revs. will be intouch.

Thank you all once again.

 

Well i now have the engine back in one piece and running but for the life of me she will not run under 2500 - 3500 revs which is not good after just replaceing the head gaskets. I have checked the timing on the main crank and that was set at TDC with the cam shafts in alignments with that. I have tried to turn the distributor to slow the engine down to no avail. I have checked for air leaks, there are none. Manual states 4 degrees BTDC. Stupid question but should the rotor arm be aligned to the no 1 cylinder.

 

There is definitely an air leak or a throttle butterfly not closing properly.

I suggest you remove the air cleaners and look at the throttle butterflies. If they are definitely closing right up, start the car with a friend's help block off the throttles completely with a large rag/towel. See what happens: ie if the car stops or keeps running. If it keeps running there is a leak!

Greg

 

Are the air filter housings in place? The rear housings that bolt to the throttle bodies? If not you have a huge air leak (via the eight open bolt holes) and the engine will run very fast!

Cheers
DD

 

I have been able to trace the air leaking issue to a couple of issues, The rubber connecting the engine breather pipe to the pax side air filter houseing was perished but only from underneath so have replaced that, the grommet holding the supplementary air valve to the drivers side air filter had also perished so have replaced that. Other issue is the cable connecting the ecu to the air temp sensor in the pax side air filter has broken at the connector so will replace the cable and the connector and re-route it away from any direct heat. Most of the engine wiring is original and now 30+ yrs old so is causing issues. Have already rebuilt the ignition loom with new wire and connectors and that is working fine now, Every thing else seems to be sealed and working fine, Have the revs down to 1300 now so expect to get it down further, then find a decent garage in Ballarat Vic Aus to tune the engine correctly.

An immense thank you to all whom have helped with you advise and help. And a Happy New Year to you all.