V8 Head Gasket Replacement

I have a Defender 110 V8 3.5L (1985) dual fuel (petrol & LPG).

Just been over to Rpi Engineering in Norwich. Great crowd - very helpful. Went there to have a power plenum fitted to my Weber / Edelbrock carb. The LPG had stopped working and I have a "popping" noise through the carb.

When they took the oil filler cap off I was treated to what could be best described as a puffing chimney belching out.

Much humming and pondering. Best view was that the head gasket had gone and back pressure was coming out through the carb. What to do is the question! I was offered the option of a 4.2 engine replacement - which is so attractive particularly given the increased torque and improved fuel consumption. Or I could replace the head gasket with the warning that other things might be wrong.

Spent lots of time thinking and talking with my friend who has rebuilt his Riley engine many times. Lots of tips - some of which I will list in this thread as work continues. Decided to go for rebuild first - if I discover that it's more than the head gasket the replacement the 4.2 becomes the next option - where do I find the cash!?

Oh - the LPG was fixed very easily. Turns out the blow backs through the card had jammed the plate that sits on top of the card in the open position. In the open position the LPG will not fire. Once released the LPG works.

We decided not to fit the power plenum as it would make matters worse whilst the V8 is in the sick condition.

Unless I have missed it I cannot find either a YouTube or web write up with pics of what to do - now all the threads do say it is easy but I really do like to have something to follow - perhaps I will have to do it myself. Keep you all posted

i would also be inclined to replace the cam as that is what is casing the blowing back though the carb! when the head gasket goes ona v8 it is more likly to be on the coolant side rather than the oil side but if you are replacing ditch the third row of bolts as they are not required

vougese39

Thanks for your reply. With the aid of my camera phone (to record where things have come from) I am at the point today where I will remove the Edelbrook carb along with the valley manifold. I then was going to concentrate on the offside. On the nearside I have to remove the air conditioning compressor and LPG evaporator - so thought I would leave that to last.

I am very interested in what you have said about the cam being the cause of the carb popping. You have not said it but are you of the view that the head gasket does not need replacing?

What I did not mention is that after the drive to Norwich (3+ hrs) there was oil pooling in the nearside valley (side with oil filler cap). Lots of pressure in that side must be pushing the oil out. Some oil in offside but not as much.

I recently replaced the water pump and some pipes as they were leaking. Still have a small leak in the rad - but not excessive and I do occasionally have to top up - but not sure now if that is water leaking via the head.

When I am cruising the popping is missing and the tone of the engine is normal - though I may have lost a little bit of performance but not certain. Popping only occurs when I move accelerator.

I have had the LR about 19 years. Don't do lots of mileage (4/5K pa). I had the cams replaced about 17 yrs ago.

Would welcome your feed back

it sound like you are intending keeping the car, youve had it half my life so far!!! if i were you i would look to replacing as many parts as you can afford to do. a complete rebuild will bring the engine back to near new condition.

you would then get at least another 17 years out of the car, body/chassis permitting.

if you can do it over a longer period to spread the cost/save for the extra bits then it would enable you to do it easier and less financially draining.

the v8 pushrod engine is a very simple engine once all the gubbins are removed from around the top end.

i find that tapeing things together with masking tape helps keep things in order and you can write on the tape. also zip bags and freezer bags can save alot of searching for smaller bits!

and the main thing is do not throw anything away until you are finnished, you never know what you might need!!!

I think if I were in your shoes I'd go for the rebuild too. The old 3.5 isn't the most powerful of the Rover V8's but it is undoubtably the most reliable & I have heard that the 4.2 is fragile at the bottom end. If £ wasn't a concern then you could always have the original 3.5 'stroked' to 4.3, but would that leave it with the same weakness(?) as the 4.2 I wonder.

I think the 3.9 is as tough as the 3.5 but a little more powerful.

Its when they changed up to the 4.0, 4.2 and the 4.6 that things started to go wrong, it was all to do with the "minimal metal condition" of the new blocks.

the 4.2 has been around a lot longer than the '4.0' it is a 3.9 block with longer stroke crank said to have come from the never released diesel v8 lr designed yonks ago so should be just as 'reliable' as a 3.9, many classic lse's have clocked well over 150k on an original 4.2, i know i got one

Thanks everyone.

However - I am committed to getting the 3.5 going again. Much as I would like the larger variants. Coming back to my earlier points. Was planning to replace head gaskets but a suggestion left hanging is that the cam(s) shafts may be the cause of the card blow backs not the head gaskets.

This is very much a working vehicle so I am rather keen to get it back on the road so a full rebuild is out of the question - my wife will also really get fed up if I take over her car for too long. So just want to fix the carb blow backs.

My thinking is to take the cam shafts out and check for wear and if OK then continue and remove heads to check gaskets.

Is there a strong view that I should replace the cam shafts no matter what I find?

Thanks

As I have stated before RPI engineering are past masters at Fear Uncertainty Doubt.

The 3.5 is without a doubt the most robust of the lot. I would suggest that your backfiring and smoking is likely to be tipped heads caused by third row bolts.

I think you will find that the cylinders are blowing into the valley as mine is.

Bar 10 mins work, one valley gasket and some coolant you have nothing to loose if the cam is half reasonable having the head gaskets done and trying it.

If you go the RPI root it will be head gaskets/cam/lifters/duplex timing chain and no doubt they will want to flog you a set of rockers too.

It's on another forum, but we did a complete strip out and fitted a short engine to our Discovery 2 V8. Lots of pictures and commentary on what we found, the engine that was in there has pressurisation problems, and was a 4.6, not a 4.0.

Bought a new Rover short engine on the 'bay, did the rest ourselves. Has done 6000+ miles since then (May) with no problems.

Use composite gaskets!

New V8i 3.9 Disco owner - Land Rover UK Forums

Make sure you have the correct torque settings available, and also a copy of the RAVE manual for your engine.

Peter

as you have now explained some more of the issues you have then i would be inclined to think you also have a well worn engine and may need a new set of piston rings as these will cause the oil pressure leakage problem.
as for the comment of tipped heads crap as the inlet manifold would have burst from the crank case and cylinder pressure under it!

wrong it only seeps a few psi and raises valley gasket slightly-is well documented both by RPI and various mg/v8 forums and mine did exactly that.
Caused sticking oil relief valve when hot.
Further to this on the v8 the inlet manifold is bolted to the heads, the valley gasket also does inlet manifolds and has a breather at back of valley, therefore the valley gasket may raise but bursting is very unlikely.

(oil light on when hot)

Google it before you disregard it as well known
http://www.v8engines.com/engine-4.htm
section "Pre-96?, then this is your Head Gasket Problems"