Rebuilding my 300Tdi

After the requisite tetris involved in getting the engine onto the crane and out of my garage, it was off to the machine-shop again this morning to resolve the cam bearing issue.

Essentially, we had two options:

1) Order a new set of bearings, wait for them to arrive, and then find a time to make yet another 1.5 hour round trip to pick it up again.
2) Establish a new hole in the bearing that communicates with the oil gallery.

Pulling the bearing out and reinstalling it is not really acceptable, as they are an interference fit and won't be as tight in the bore second time around.

Considering time, effort and relative risks and benefits of each, we decided that it would be fine to put in a new hole. Fortunately, the gallery also heads vertically up to the block face, and so a long drill was gently used to get through the backing material, and a fine punch used to make the final aperture through the bearing surface. It was then cleaned up with a bearing scraper. The hole is not perfectly round, but it is in the right spot, and in size it is midway between the allegedly unsuitably large original hole and the disconcertingly small replacement hole. Best of both worlds? We'll see, I guess.
https://www.aulro.com/app/data/1464/...831_200539.jpg

Hopefully the con-rods and main bearings will arrive any day now, so I can get on with getting it all together.

Quote:

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Originally Posted by Lionelgee

Who would be fault for the incorrect placement of the bearing?

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That would be the machine shop who installed them, hence why I took it back. [wink11]

Totally agree that Hobnobs are fuel for thinking! I'll be sure to overindulge, at your behest.

Quote:

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Originally Posted by Shonky

G'day Lionel. Glad you're enjoying it. [bigsmile1]

The original front cam bearing had two large holes, that correspond with two similarly sized oil galleries in the bore where the bearing sits.


The lower hole is where oil enters from the main gallery and lubricates the bearing as it turns, and some of this oil escapes out the second hole at about the 1 o'clock position after it is carried around the bearing. This second hole is the gallery that runs between and around the cam follower guides, which themselves have oil holes in them to let oil in to lubricate the rollers and slides.

On replacement bearings, this second hole has been greatly reduced in size. I have heard that this was to keep the oil pressure up in the bearing to improve wear.


The problem in this occasion is that the bearing was installed slightly clocked around from where it should have been. This was not an issue for the lower hole as it is large and really only needs to be at least half-lined up. The upper hole though, being so small, was now not lined up with the gallery and hence was a hole to nowhere, with the gallery blanked by a section of bearing with no hole in it!

I hope that makes sense. I'm about to post up some pictures which hopefully will show what I'm waffling on about. [thumbsupbig]

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Great read.

Question. If the engine was rebuilt with the oil feed hole smaller than normal AND not lined up correctly, what sort of issues would one expect and how quickly would something happen?

Quote:

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Originally Posted by BreakingBad

If the engine was rebuilt with the oil feed hole smaller than normal AND not lined up correctly, what sort of issues would one expect and how quickly would something happen?

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That's a really good question, and one I couldn't help but ponder myself...

I assume you are referring to only partial misalignment of the small hole, in reference to my statement that the large hole can be misaligned by up to ~50%? Complete occlusion is the same outcome regardless of hole size, of course.

Like this, but on the small hole?
https://www.aulro.com/app/data/1464/...902_160017.jpg


The short answer is, that I don't know for sure. My understanding that the oil galleries only need to be at least half uncovered comes from reading around and talking to my machine-shop, but isn't something I have first-hand expert knowledge of.

I can only imagine that being such a tiny hole, you'd really want all of it open!

As for what the outcome of reduced oil flow through this hole might be, it's worth noting though that whilst the cam bearings are internally oiled, and the cam-lobe for the vacuum pump has an oil jet pointed at it, the rest of the cam lobes are lubricated along with the followers and slides from this oil gallery. As far as I can tell, the entire top-end is also dependent solely on this gallery for oil supply, so you if oil supply was inhibited, this would affect the rocker shaft and rocker arms also.

Depending on how much the hole was occluded, you might get anything from slightly accelerated wear of the above components over many years, to rapid damage to the oil-starved top-end and cam, potentially resulting in catastrophic failure when something breaks and introduces your valves to your pistons.


EDIT: I have amended this post after closely inspecting the cylinder head and discovering that it too is completely dependent on this oil passage. I previously thought it had additional or separate oil supply and as such would mitigate some of the poor lubrication of the camshaft by letting oil onto it down the pushrods. This is not the case!

I just went and stuck a few torches in the camshaft bore, and pulled the blanking plug to see how it's all connected.

To reiterate: oil comes up through an oil gallery from the oil pump, and into the front cam bearing via the lower hole. It then does a clockwise loop to lubricate this bearing and some of it is forced out the top hole, which is out of shot. If you look through the threaded hole, you can see the small passage where the oil comes up into this gallery. The light is showing out the top of the cam follower bore, and if you look at the follower assembly sitting on top you can see a broad groove in it to let oil around it and through the next gallery into the next one, then the next, and so on. Note the hole in the side of this assembly, which lets oil into the follower guide (which doesn't move) to lubricate the end of the pushrod, which sits on the slide, which sits on the roller follower, which sits on the cam lobe.

https://www.aulro.com/app/data/1464/...am_oilway1.jpg
NB: This image has been edited to enhance the illumination of the oil gallery to the head.


Critically, it also comes up the small hole at the front left corner of the block face, and into the cylinder head (around one of the head-bolts!) to supply the rocker assembly with oil, that then runs back down the pushrods towards the sump via the cam followers and cam lobes also. Follow the red wire.

As best I can tell, this is the only oil-supply to the head!

https://www.aulro.com/app/data/1464/...902_170757.jpg

On to the next rabbit-hole. This is probably a boring, wordy post.

I hope you all don't mind, but I'm largely using this thread to data-dump a lot of the over-thinking I've done about various components. As a novice engine-builder, and in keeping with the intent to mitigate incompetence with diligence, I've probably spent a long time navel-gazing over things that probably don't matter. Until you know they don't matter though, it's hard to make that call. Maybe this will one day save someone else the trouble.


One of those things was piston to bore clearance.

My cylinder block came home from the machine-shop nicely bored and honed, with excellent dimensional consistency within and between the bores, measuring up at bang-on the book value of 90.980mm for a +0.020" oversize job. I did notice that only one of the four piston boxes had been opened, so clearly the machinist only measured one, but this is a Land Rover not a race engine and this is surely fine.

The 300Tdi Overhaul manual specifies a piston to bore clearance of 0.075mm, measured with a feeler gauge. It was hard to know if this is a benchmark or a maximum, but it says that if it is over this, then the cylinder must be rebored.

https://www.aulro.com/app/data/1464/RTFM6.png

Despite following these instructions, the largest feeler gauge I could get down beside the piston was 0.038mm, and even then, it was way too tight to be diagnostic of that value. This was confusing, as the cylinders are freshly bored to spec, and the pistons are new.

Putting grandad's feeler gauges away, I decided to stick to more accurate instrumentation and do some reading.


I am rapidly forming the opinion that unfortunately the official literature should be taken with a grain of salt. It is very useful, and absolutely a necessary reference, but I've come across more than a few things that are questionable, inconsistent, or objectively incorrect.


My thoughts on the specified maximum of 0.075mm cylinder to wall clearance? It's bollocks, and here’s why.

Unless I'm missing something, Piston to bore clearance = bore diameter - piston diameter

If you subtract the STD piston size of 90.395mm from the STD bore size of 90.470mm you get... 0.075mm. So rather than being a maximum, this is what it was when it was brand new. Obviously wear happens, and is normal within an acceptable range, but the manual does not provide this data for piston to wall clearance.

By way of contradiction, the same book gives the bores a permissible bore wear value of 0.177mm maximum, which of course will affect your clearance. On the one hand, wear is acceptable, and on the other allegedly it is not. Curiously, calculating theoretical clearance for an engine with STD pistons and at maximum permissible bore wear gives you a massive 0.252mm. That's 0.010"!
[bigrolf]

If you want to really get lost in minutiae, even the book values for oversize assemblies do not agree with the 0.075mm maximum. For +0.10" it comes out to 0.081mm and for +0.020" it comes to 0.077mm - so technically if your specs are exactly right on a rebored engine, your clearance is out of spec. As it stands, the "+0.020" pistons that I was delivered were stamped as being 90.895mm anyway, which is less than the 90.903 in the book. (by 8 microns, or the width of a red blood cell…) This will give you a clearance of 0.085mm.

In actuality, there was a reasonable variation between the actual piston diameters.

For reference, this was the dimensions of my fresh bores and new pistons:

https://www.aulro.com/app/data/1464/...Clearances.jpg

As you can see, only one of them is close to book value. The others are out by as much as 0.025mm over or 0.015mm under.

tl;dr: So after what has been a very long walk for a very short view, my conclusion is that I am going to ignore the official overhaul manual’s guidance to stuff a feeler gauge between my pistons and bores to measure clearance, and use the ideal value of 0.075mm as a guide only.

It is doubtful that these things were built to finer tolerances than the ones I have, and even the cylinder that technically has inadequate clearance is only 15 microns under.

I didn’t know if this was okay initially, but now I’m sure it is. And that is the point of all this. A fresh engine is really the secondary outcome in my case. The primary end-point is learning. [thumbsupbig]

After a hefty wait for my replacement conrods to arrive, along with my main bearings, last week a package finally arrived.

It contained a number of other parts I had ordered, but no bearings. So that was quite irritating. After calling the supplier to harvest my deserved apologies and promises of reparation, I thought I'd double check the rest of the parts.

Curiously, one of my conrods was a different brand to the other three. It seemed nearly identical, until I looked closely and noted some slight differences in the casting. The part number was identical though and it certainly seemed functionally correct.

https://www.aulro.com/app/data/1464/...908_170803.jpg

https://www.aulro.com/app/data/1464/...908_155754.jpg


Once again, it pays to check all new parts very thoroughly.

Putting the rods over the scales, the three like-branded Bearmach (RIP) ones came in at 1217g, 1219g and 1220g - not an unreasonable variation I thought.

The mystery branded one, however, was a substantial ~30g heavier at 1248g. This may not sound like much, but on a rotating assembly doing thousands of RPM I imagine it would make my nice new motor run like a washing machine with a brick in it.

https://www.aulro.com/app/data/1464/...918_091545.jpg


So once again I called my supplier. Once again promises of rectification were made. Once again apologies were extended. They have been otherwise very helpful, so I'll cut them some slack.

Since this workshop also has extensive experience rebuilding Land Rover components, including engines, I also ran my piston-bore clearance questions past him. He also concurred that the 0.060mm minimum clearance is perfectly fine, and is indeed more than the 0.050 that he aims for in his builds, so that was reassuring.

It might be another week or more before more conrods come in, so apologies for the lack of updates. The camshaft is back in, and the vac pump, lift pump, cover plate and filter head are in situ, and I have resorted to repainting all manner of peripheral components, because I've run out of things to do until the crankshaft and pistons can be assembled into the block.

https://www.aulro.com/app/data/1464/...904_161038.jpg


As an aside, I wonder if 300Tdi owners should check their "camshaft oil-feed plugs". These are the three rubber plugs that blank off drillings that go from the top right of the block down to the second, third and fourth camshaft bearing bores. Mine had completely disintegrated, and would permit water and detritus to accumulate in these drillings and sit behind the cam-bearing shell. I'm not sure if this would be much of a problem, but I'd rather like to not have mud sitting anywhere near what are supposed to be internal components...

They are easy to get to, and available with part number ERR5034.

https://www.aulro.com/app/data/1464/...904_134411.jpg

This rebuild is going nowhere at the moment.

It's now been almost a month since I first ordered new conrods, and when three more arrived this morning to make up a matching set, I thought I could finally crack on and assemble the engine.

It was not to be.

Furthering the lesson that just because parts are new doesn't mean they are good, this was the small end bushing of one of the new rods.

https://www.aulro.com/app/data/1464/...926_103317.jpg


Neither the supplier nor I could find any more in the country, so now I'm waiting for another 2-3 weeks for another rod from the UK. In the meantime, I have no less than 11 conrods sitting on my bench, of which 6 are usable, but not together. 4x original ones that are dead, 4x matching new ones but one is defective, and 3x matching new ones that need a fourth.

https://www.aulro.com/app/data/1464/...926_121925.jpg


To say I am less than pleased would be putting it lightly.


This morning I tidied up the garage and covered everything up. The replacement won't arrive before I have to go interstate for nearly a month, so I'll see you all in November.

****. [bawl]

Hi Andrew

I have three from my old block if you need.

I am nearly finished adding all the ancillaries to my rebuild block. I sent all the alloy parts off to vapour blasters and will pick them up tomorrow so I can then get the block all finish.

Are you reusing your cylinder head? Mince is toast with a crack somewhere in a water gallery near the valves at number two piston. i am going to order a performance head from Turners in England.

I also have a set of four rods that came out of the 300tdi. I bought/had fitted a new complete set of rods/pistons from turners for the rebuild.

Located Bris.