3.5 V8 Carb Engine Blow Back after cam Shaft replacement

Hi all,

well, it's been a while since visited here... mainly two reasons so, one the old RRC was running fine (-ish, well, good enough) and the care she needed was only available at a workshop, since the one week-end job of replacing the camshaft did materialize for over a year. The seocnd reason was a new job, and the resulting lack of time to do anything else than doing some small bits of work in order to get her through her 2-year technical inspection.

So, the new cam shaft is in, a Kent H200. TÜV was passed successfully except for some small bits (the tow hook has to be reattached, I need new window wipers, a new front light bulb and a certificate for steel braided brake hoses). Since the new cam shaft is in so, there are some weird issues:

- loss of power when hot at above 2.5 to 3k rpm -> seemes solved with a new temp adjustment thingy (no idea how it really called) for the carbs

- impossible to consistently et idle rpm to below 1k without the engine dying (was no issue for emissions testing, but still not normal)

- engine blow back -> the exhaust had some holes, which are now welded; it happens independent of acceleration and load, with a tendency to happen more often with a warm engine and when going of the gas, it does happen regardless even when cold and idling

I did check the workshop manual, and since it is not happening when accelerating, I think it is related to the valves and /or valve springs along the rocker. At least symptoms are inline with what the manual says.

Now i have two general questions:

1) is the root cause correct? I don't want to spend money on parts and mechanics for nothing

2) if it is the valves, springs and rocker, I am very inclined in going straight for upgrade two on my list: new cylinder heads, and new rocker assemblies as those aren't that expensive. The engine isn't really tuned, with the exception of the new cam shaft, so I am thinking of stage one heads. back the day, I looked at V8 Development heads or the gas flow ported ones from Turner Engineering. Any experience or opinion of those two options? Price wise they are very similar.


Anyway, I hope you didn't mind a very prolonged absence, it looks like I might be a bit more active again in the near future!

Greetings!

How sure are you that you got the timing marks lined up? A tooth out and you'll have problems

I dont know the full ins and outs but a Kent 200 will have a higher lift and longer duration on both inlet and exhaust.

So expect it to run lumpier than standard at low revs.
To go along with this change were there any recommended changes to the ignition timing and fuel jets? and as above ^^ was it timed correctly.

Being only a "mild road" you should be able to get it to run pretty well at a bit more than normal tickover.

Dont forget it sucks longer (more fuel needed) so may need an adjustment on the fuel side too. also opens inlet before exhaust closes earlier which can cause blow back if the exhaust is not working properly.

Its quite scientific really when you get into it.

J

I had the work done at JLR, and the timing gear setting was easy enough, just set the gears according to the markings. Also, ignition is working perfectly, even better than before honestly. Well, the exhaust has been on back order for a while anyway by now, so we'll see how that works out once the new one is in.

Any insights in V8 Developments so? I got the misses convinced that new heads and rocker might be a necessary and a good investment!

So, just came back from a Land Rover meet up at a friends place. And I learned one or two things about my problem from a friendly land rover mechanic who was also there, and from the test we did:

1. The blow out in the exhaust is most likely due to a broken exhaust sucking in air -> we'll see soon enough as the exhaust was delivered today.

2. JLR, for some reason, mis-adjusted the ignition, hence the high idle rev of 1.2k. Turning it down a bit to around 800 made the car driveable on the road

3. The engine has n power to speak of, makes barely 110 km/h on the highway and dies on the slightest climbs at my friends obstacle course

4. The fun, and important, bit: There is blow out on the right carb, intermittently and starting at around 2.5 to 3k rpm.

5. With the readjusted ignition, and carbs, there is no more blow outs from the exhaust

Where the friendly mechanic and I did find agreement was at diagnostics. He thinks it might a badly installed timing chain, and he does have a point here. On the other hand, wouldn't a timing chain issue cause the same issues on all cylinders and not just one bank? To me it feels more like a valve issue, as valves and valve springs have never been changed as far as I can tell ever. Also, the mechanic thinks that not all cylinders are firing, and I agree.

The plan of attack is now to install the new exhaust, replace the spark plugs and do a compression test if that doesn't help.

Any thoughts? Despite having the go from my government for new cylinder heads and rockers, I'd kind of not spend 2k € right now... In case it is the valves / valve springs, is that something one can do at home with neither a lot of time nor knowledge working on engines?

Greetings everyone and have a nice week-end!

hef19898 said:

Any thoughts? Despite having the go from my government for new cylinder heads and rockers, I'd kind of not spend 2k € right now... In case it is the valves / valve springs, is that something one can do at home with neither a lot of time nor knowledge working on engines?

Greetings everyone and have a nice week-end!

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You'll need to take the top end apart & if you're going that far then you might as well take the front cover off while you're at it & you can then check that the timing chain & its sprockets are right or not.
I think that does need to be done if only to rule it out.

If it was running fine with the same valves & springs before all this was done then it's not the valves & springs.

Ah ****, I was affraid someone would confrim that... Regarding the valves, that would only mean taking the rocker cover off, right?

The front means draining the cooling system, removing the radiator and then it is just the cover, right? No messing with oils and other liquids?

Because complaining to JLR doesn't do any good, the garage was sold to a chain with a below-zero policy regarding those things or more budgety repairs. And, if it is the timing gear, they already botched it once anyway...

Well, exhaust first, then spark plugs. Then we'll see. If the work is beyond my time / skill, I'll bite the bullet completely, go for new rocker assys and heads and have it done, ideally with me being there, by the garage my old man found (a one man shop who does everything from old VWs to Defenders).

Thanks anyway so far, I'll keep you all posted!

Before you do anything, do a compression test. You don't need to undo anything other than take the plugs out for that

Compression test sounds good! One other thing so, the right hand carb (the one with the blow out) and the exhaust have black soot... Is that only fuel not properly burned, or oil? Please tell me it aint oil!

Don't worry about that just yet, if it's soot then it's nothing major at this point

Thanks, that is some calming news for this Sunday!

hef19898 said:

Ah ****, I was affraid someone would confrim that... Regarding the valves, that would only mean taking the rocker cover off, right?

The front means draining the cooling system, removing the radiator and then it is just the cover, right? No messing with oils and other liquids?

Because complaining to JLR doesn't do any good, the garage was sold to a chain with a below-zero policy regarding those things or more budgety repairs. And, if it is the timing gear, they already botched it once anyway...

Well, exhaust first, then spark plugs. Then we'll see. If the work is beyond my time / skill, I'll bite the bullet completely, go for new rocker assys and heads and have it done, ideally with me being there, by the garage my old man found (a one man shop who does everything from old VWs to Defenders).

Thanks anyway so far, I'll keep you all posted!

Click to expand...

To do the valves you need to take the cylinder heads off.
The rocker covers need to come off.
The inlet manifold has to come off. That means draining the coolant, taking all the hoses, cables & linkages off.
The exhaust manifolds really need to come off if only to reduce weight & make it easier to manouevre the heads out.
Then when you refit you will need new head gaskets, new inlet manifold gasket & valley seals, new exhaust manifold gaskets & unless they're in VGC new rocker cover gaskets - the later rubber ones are much better.
When the heads are refitted don't bother with the outer row of bolts. The two main rows are all that is necessary & LR did away with them altogether on late vehicles. If you do want to fill the vacant holes put them in but just nip up.

Not being funny, but if you needed to have the cam fitted by a garage then I don't think your mechanical skills are up to it as although it requires a lot of dismantling it's an easy job.
You also say your time is limited. For an experienced mechanic/DIYer it's not a long job but it it's your first time it will take a lot longer.

Whilst it IS possible to change the springs without taking the heads off it's really a pointless exercise as you won't be able to see the important end of the valves & the valve seat faces.

Ratae, you are right regarding my skills and time. So, new exhaust (needed anyway, the old one is a sieve), new spark plugs and a compression test. After that, we'll see. Since I need to pay someone anyway, heck, I'll propably go for new, pirted heads and new rocker assys.... Fingers crossed that isn't needed right away!

I could bite myself so, if the exhaust manifolds need to come off as well, I could have went for ab ports exhaust!

Much easier to take the exhaust manifolds of the heads than to separate the downpipes from the manifolds.
Plus, the heads are easier to manage without the manifolds attached

Kermit-rr,

let's hope it doesn't come to that! Compression tester is ordered, so next week I'll know more! And as soon as the heat and sun goes away a bit, I'll attack the exhaust.

Ok, so, I did the compression test... Doesn't look too good in my opinion, but I can't actually tell. Test was done with budget (no chinese crap, but I don't pressure curves) tool.

Results as follows:

Cylinder 7: First turn 5.5 bar, max pressure 8.5
Cylinder 5: 5.5 and 8.5 bar
Cylinder 3: 5.5 and 8.5 bar
Cylinder 1: 5.5 and 8 bar

Cylinder 8: 5.5 and 8 bar
Cylinder 6: 5.5 and 8 bar
Cylinder 4: 5.5 and 7 bar
Cylinder 2: 5.5 and 6.5 bar

Spark blugs all had 0.75 mm between contacts, Bosch. Cylinders 2, 3 and 5 showed black soot, picture attached.

The workshop manual says minimum compression pressure of 9.5 kg/cm2, that would be just above 9 bar. So, any thoughts?

Next steps would be new ingnition wires, which I have on hand to replace the Bosch ones, new spark plugs (BPR6ES from NGK, to be set to 0.6 mm) and a new exhaust.

Not sure whatbto make of all that...

I found the results of a compression test from 2013:

Nice curves from 4 bar all the way up to 10 on all cylinders...

So, JLR managed to install the Cloynes timing wrong or Tunesia killed the head gasket?

Wonder why 2&4 are a bit low?
Those plugs look ancient!! Get some new ones

Honestly i would say 8.5 is a bit low too, I'd like to see 10 minimum

I'd do a wet test put some oil down the bores and try again. It helps to seal the rings. Do you get much out of the oil filler cap?