12j reassembly

sure as I can be about the timing but when I did the leak down test, I backed off the tappets to ensure theŷ were closed.
Valves were lapped and fluid tight on the bench,once turned over on the vehicle 2 cylinders are leaking badly. No idea why but this has happened multiple times. I've only just realised what's happening and I think it's been the problem from the beginning.

Haven't had a look at this thread for a while - did you get sorted? Looking at the total lack of ignition on those two cylinders I thought of timing/fuel injection issues rather than low compression.

Wouldn't say sorted (don't want to tempt fate). It has started but not run for long ( no coolant).
Think it was a combination of issues. The valve and injection timing were retarded by a tooth. First couple of times I did it, it was checked and rechecked loads of times. The last time I got over confident and didn't recheck it.
The injectors have been reconditioned as the spray on two of them wasn't that good.
More work on the head. A couple of the seats were cut a bit wide and some of the inlet valves were trued up even though they were Oem.
Seems like all together, they prevented starting.
Weird thing is, when the head went on, I left the valve gear off and did a leak down test. The valves still leaked even though they vacuum tested ok and didn't leak fluid.
Test pressure is 80psi which seems low compared to combustion pressure so I don't know what to make of that.

for interest guides ca obviously replaced or reamed out ,bronze linered then broached to each valve ,not that yours need doing

When last we met, the engine was running but only on two and a bit cylinders and not very well at that. A local agricultural engineer recommended driving the engine hard for a while to bed in the valves. Wasn't convinced by this but tried anyway. Didn't work; maybe it would on a tractor but not mine.

Completely sick of it by now, it was just left in the garage. After a few months,l decided to have the final battle. To the death. Either it goes or I do.

The main problem was no compression on cylinder 1 and lowish on cylinder 3. I was convinced it was the head casting because you could feel gas pulses coming from the inlet manifold and hear leakage.
So I went to turner engineering for a recon head. First question they asked was who did the head. When I said "ACR", they said "say no more". Not really sure what to make of that.
First hurdle was that they wouldn't accept my head because it was a "cheap indian casting". Eventually I got a complete head. Which I eagerly fitted...
No difference. Bugger! (Actually slightly better compression on cylinder 3 but still nothing on 1).

At a total loss now. Head replaced, tappets and valve timing checked endlessly. And still exactly the same problem. There seemed nothing else left to do. Or was there?

Still thinking there was a problem of some kind with the valves. So I got out the timing disc, dial gauge and workshop manual.



Checked the mark on the crank sprocket (exhaust peak on cylinder 1) and found it to be 109deg BTDC. As in the manual.
The mark on the cam sprocket is linked to the crank by the belt so can vary a little. I found the exhaust peak, open and close all to be off the manual values by varying degrees. But given that one tooth on the cam sprocket is 7.5deg and the actual exhaust peak is about 4 deg, it seems acceptable. The main thing was that the measured duration was 250deg which is within felching distance of the manual's 244deg.

But the inlet was miles out with the open advanced and the close retarded giving a duration of 262deg which is way over the manual's 238deg.
So I guessed that the inlet was open when it shouldn't be and that caused my symptoms. (Or was wishful thinking depending on your point of view).

Ordered an Oem cam for £56. The new cam was much better finished than the ACR one (which I concede doesn't really affect function).
I wanted to get the two cams profiled to prove any difference but hamlins didn't really want to do it and wanted £100 per cam as they'd have to set it up for machining the profile. I guess a specialist camshaft company could do it,but I don't know any so I took the gamble and fitted the Oem cam.

So after fitting, I measured it again and this time was with a couple of degrees of the manual. This seemed acceptable given the limits of my measuring and manufacturing tolerances. The marks on the cam sprocket in the picture below span the width of exhaust peak (about 4deg). Doing the valve timing was a bit of a pain because the middle of the peak was either 3deg retarded or 4deg due to the granularity of the cam teeth (7.5deg). I tried both positions with no obvious differences (would need to get it on a dyno - and that's not going to happen)



Then tried to start it.

Little bit of cranking and it started. And ran on four cylinders (not that well mind). Don't know how it's possible for a cam to be that far out. Hamlins said it can happen but it's very rare. Maybe I'm just lucky.

I'm not going to refit the old cam to prove it so it stays in. The engine ran well enough to pass the mot, although the tester commented that it was spitting back through the intake manifold and was down on power.

So still more work to do.

Have you timed the fuel injection pump yet? Mine ran but to get it running right I ended up using the timing kit to set the pump rotation just right. Ran rough at first but it soon ran better than ever.

Every time the valve timing is set (which is lots), I do the fuel timing. I have also tried rotating the pump while the engine is running, which is interesting.
It changes the idle speed but I'm never really sure which is better or worse.

So the engine runs but not well at low revs and doesn't start well. Still seem to be problem with in inlets on cylinder 1 and 3.
Abit desperate now, I noticed that the valve stems of the inlets of 1 and 3 protruded slightly from under the rocker pad. Cylinder 1 photo below.



Clutching at at straws, I wondered whether the side loading on the rocker was stopping it closing fast enough. So I took off the valve shaft and rejigged the spacers to get the rocker square on the stem. As below



Put it back on and it started and ran beautifully. Feeling incredibly pleased with myself, I bolted on the radiator, water pump, rocker cover etc. And started it.
It was crap again.
A quick compression test shows nothing on cylinder 1 or 3. Again.
How was this possible? Just bolted the cooling system and the rocker cover and suddenly it's lost compression.
Couldn't be the water pump etc so I took off the rocker cover and started it again. Perfect. So time to look at the inside of the rocker cover.

Below is a picture of the witness marks from cylinder 1 inlet rocker. This must have been holding the valve open long enough to lose compression. There were similar marks on cylinder 3 and 4.



I drilled out the bolt holes by 1mm and machined recesses where the witness marks indicated it was required. Then bolted it down and it ran perfectly. Finally.
Why, I have no idea. The rocker cover the right one and is genuine. The rockers they supplied were pattern and looked a bit bigger at the pushrod end.

Still not too much of a problem and only took a year to find.

A test drive revealed a smooth motor but not much power. Then I noticed the front brakes were binding. Ho hum.

Wow! Bit of a head f**k that (pun intended) bet you are glad you found those marks. Glad you've got it sorted.

Jam1 said:

Wow! Bit of a head f**k that (pun intended) bet you are glad you found those marks. Glad you've got it sorted.

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Glad is not the word. But I'm kicking myself for not realising earlier, it explains all the disappearance and reappearance of compression. I blamed my eBay compression gauge and started not to trust it. Guess I have to apologise to it now.

Now it's funny you should find that it looks like the rocker has been hitting the cover but I have read about this before. I think it was on a site called mud4fun , it's down now as the owner got fed up with the trolls, he had the same issue and had to grind the back of the rocker down. I've bought a set of rockers from Turner and 2, i think, of those have been machined at the adjuster end to make them smaller. One to watch for folks.

I'm just swearing at my head as I am doing a full recon and those bastard hotspot pins grrrr

no pins on my 15J they where staked with a centre pop on the circumference. Head was not drilled for pins!

Blackburn said:

no pins on my 15J they where staked with a centre pop on the circumference. Head was not drilled for pins!

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should have been they are the only thing that locates then correctly

Interesting, I didn't find any references to that problem. But if they grind down the rockers, it must have happened before. I didn't really fancy grinding the rocker in case it affected the temper or strength.

Yet another point for turners over ACR.

Epic thread - thank you for taking the time to put it together. How are ACR still in business when they are supplying parts and service of such low quality?

zeaphod said:

Epic thread - thank you for taking the time to put it together. How are ACR still in business when they are supplying parts and service of such low quality?

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Thanks. I'm still collecting my thoughts on ACR. Not all their engines can be like this, I think I must have had the new boy - I mean missing cam thrust plate and blasting grit all over the place, ffs.
It's not easy to find opinions one way or the other, they don't belong to an industry body, trust pilot or claim an iso standard so how do you know.
I don't like to make snap judgements but they won't be top of my list next time.

Many thanks for sharing your tales of woe!
I must have been extremely lucky, as in all my years of stripping and rebuilding, I have never encountered bits that didn't fit properly!
At this point I have to admit that all my pistons and rings have been Hepolite .. even on engines as diverse as a Brough Superior and a Triumph Mayflower!

SpringDon said:

Thanks. I'm still collecting my thoughts on ACR. Not all their engines can be like this, I think I must have had the new boy - I mean missing cam thrust plate and blasting grit all over the place, ffs.
It's not easy to find opinions one way or the other, they don't belong to an industry body, trust pilot or claim an iso standard so how do you know.
I don't like to make snap judgements but they won't be top of my list next time.

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I hope you're right, maybe just an extreme case of bad luck. I only have experience of Turners - which was a good experience, perfectly packaged uprated head in perfect condition.