Need help with engine version.

jp928

jp928

Well-Known Member
Just took delivery of a 3.9L I intend to overhaul for the P6B. Some aspects have me beat. Its out of a 1994 Discovery. 38D serial, suffix B, 8.13:1 CR markings. Serpentine front cover, crank driven oil pump. Block is 38A as it has the bosses for cross drilled main caps. 10 bolt heads. On these Hammil says the valves should be more recessed than earlier models, but they look like normal height to me. The pistons crowns have 22058 and X47 and M6 stamped on them. Sump is old style 14 bolt, looks same as P6B.
Pretty sure its been opened before, as all the gaskets are steel shim, rather than the composite I expected. None of the pistons have the washed look that would indicate they have seen water, although the No 8 exhaust valve is very white, where all the others look normal. The heads have been shaved, as I can easily see milling marks. New rocker assemblies , said to be ~ 3 months old , are present, with no visible wear on the shafts, but they were the wrong way around - oil holes on the wrong side. Also said to have head new lifters recently, and the 4 I have been able to pull all have very clean shiny bases. Dont believe the cam was changed when the lifters were done.
Comments please. Pics can follow if necessary to nail down anything.
thanks
 
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Got it apart some more. Will never again try to undo the front crank bolt on an engine sitting on the floor. Tried a rattle gun, and it just rotated the crank. Trapped a spanner on the flywheel bolts against the floor, and the whole assembly just rotated. In the end I had to bolt a 3x2 piece of wood ~5ft long to the bellhousing area, trapped the spanner on the crank against the end of the wood before I could get enough force into it to loosen the bolt. Using the 2ft long tension wrench it was only just enough to undo it. Balancer came off OK. Then the oil filter - same again - almost ran out of muscle trying to get that off.
Heads look like they have been shaved .010" , based on measuring the end pads shown in the book. This model has the intermediate main caps, so cant be converted to cross bolts. Cam has no retaining plate. Chain is very slack on the left side, well worn. Inside the valley shows the asymmetric machining for the lifter holes shown on the RPI (?) utube that indicate shifted cores, so probably up for top hat liners.
 
Having top hat liners fitted would be a given JP. No point whatsoever in rebuilding the engine without having that done first. The camshaft retaining plate can, so it is my understanding, restrict oil flow to the distributor drive gear, so that is possibly why is has been omitted. The valves for the 10 bolt heads are definitely recessed when compared to the 14 bolt heads, I could certainly see that on mine.

Await your photos.

Ron.
 
jp928 said:
Will never again try to undo the front crank bolt on an engine sitting on the floor. Tried a rattle gun, and it just rotated the crank.
Click to expand...

I just did that :)

But I actually took the engine out of my car myself, took the gearbox off, and the heads, then tried to remove the crank pulley :hmm:
 
Here are some pics.
jXDBsV2.jpg

Cyl 8 on left. The rest are the same as 6.
GmyfP7G.jpg

Some lifters. All are polished and pretty much unmarked. A couple have a pure circular mark, others more diffused.
https://imgur.com/n2PFhOh
Machining marks - only on left bank. Shifted cores in casting?
https://imgur.com/qtYeaTw
chain slack.
 
All looks fairly good in there, I wouldn't worry about the machining marks, that's pretty much normal.

Lifters aren't looking too good, but then you really shouldn't change them without changing the cam at the same time. They wear together so changing only one part of it will result in quick and early wear of both.

Chain slack is no worse than mine, and mine is a Cloyes set up with only 20,000 miles.
 
More questions. Just pulled the timing chain and wheels. The mark on the crank gear was a bit hard to locate, but ok. At no 1 tdc the crank keyway was at 45d from vertical. Something in my brain went ??? In the SD1 book it shows that key way at 90d from vertical, in the later LR manuals that cover 3.5,3.9 etc, they key is at 45d.
What changed along the way here, and when?To me the crank gear must have changed, AND the crank keyway relative to No 1 TDC also changed ? Coulnt that cause a headache if you mixed up crank gears from an SD1 or earlier, and a later type?
Expended some elbow grease cleaning the head faces, using only a plastic scraper....and a fingernail.
 
More.... I have 10 bolt heads, which should be 28cc combustion chambers. The piston crown depressions dont look very big, so I made a guess that the average diameter (allowing for the slope at the edges) is 70mm, and they are close to 6mm deep. This works out to 23.2cc. Allowing for a 1mm composite gasket (6.94cc) gives a total chamber of 58.04cc. With a cylinder swept volume of 493.6cc, this gives a CR of 9.5:1 .
The engine is a 38D 3.9L, and the engine no pad is stamped 8.13:1 CR. This should give a chamber volume of 69.23cc. 9.35:1 CR should have chambers of 59.11cc, which is close to my calculated volume. Anybody know the ccs for the piston crown for any CR ?
Heads are HRC2479 casting.
Am I missing something, or muffed a calculation ?
 
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Something in the grey cells tells me that the 4.0 pistons are HC, with a smaller dish, and they are used to bump CR, I am not with my notes ATM.
You need to bring a piston to tdc, finger vaseline around the top outer edge to seal it to the bore, clamp a sheet of clear perspex over the block face that has a small hole in it, and then with a syringe inject a thin oil to 'cc' the volume over the top of the piston. You cannot work out the CR without doing this, and the same with the cyl head combustion chamber. Then work out cyl volume and area taken up by a compressed head gasket.

How to Calculate Compression Ratio: 9 Steps (with Pictures)
 
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Progress. Perspex on the head, got 27+cc in the chamber. Seems about right, as the head has been shaved .25mm (10 thou)based on thickness of the end pads as shown in manual. Got 35cc into piston crown. 1mm gasket =6.9cc.....OK, comes out close to 8.13, so the pistons are correct for the stated CR.
 
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Here are some random numbers I collected and used in the past, they may help you. I am not an expert or a professional, all info given in good faith, to be verified before use.
With a 94 mm bore here are some gasket capacities compressed.
Tin - 0.4mm 2.7cc
Comp at 1.0mm 6.9cc
Comp at 1.1mm 7.6cc
Comp at 1.2mm 8.3cc
Comp at 1.4mm 9.7cc

Head skimming approx figures - For every 0.008" of material removed 1cc of combustion chamber volume is lost.

4.0 HC pistons have a 13.23 cc dish compared to something like 22.29cc for LC

I had a set of nicely prepared 14 bolt heads, unskimmed at 36cc chambers and agonised over what to do with these, I did not have the funds to change either the pistons or the heads. I used tin gaskets and skimmed the heads 0.040" to arrive at 10.2:1 CR. The intake required a bit of fettling to fit, but I am please with the results.

With 4.0 HC pistons and 28cc heads you could get a bonkers CR :)
 
More oddity. When I got this unit I pulled the rocker assemblies first, as it was claimed they were very recent replacement. Barely a mark on the hard pads at the valve end, good. First look said, Yes, maybe, but the oil holes in the shaft were around the wrong way. Further inspection showed they were worse than that - I thought maybe have to rotate the pedestals 180d, but in the end I had to completely dismantle them and rebuld from scratch to get the oil holes correct. Wonder what else I will find as I go deeper. Since I dont intend to use the serpentine front cover I put that on eabay and got $100 for it.
 
The engine arrived without the sump fitted (sitting on an old tyre). When I got it up on one end (on wood blocks) I found the oil pick up pipe is bent, slightly kinked. The genuine pickup pipes are hard to find, or pricey. Does anybody know if there is a Buick or Melling pick up that will fit? The Buick V6 (3.8L) units are apparently a bigger dia tube (good thing) , but pics are unclear that the mounting is not horizontal as this engine requires. Most of the early pickup pipes and strainers seem to be NLA.
thanks
 
jp928 said:
Progress. Perspex on the head, got 27+cc in the chamber. Seems about right, as the head has been shaved .25mm (10 thou)based on thickness of the end pads as shown in manual. Got 35cc into piston crown. 1mm gasket =6.9cc.....OK, comes out close to 8.13, so the pistons are correct for the stated CR.
Click to expand...

I have just measured my 4.0L pistons at TDC and they are between 20.4ml and 20.9ml. If yours are 35cc with a 27cc head and composite gasket your CR works out at 8.15:1.

Can you bend the oil pick up back to shape?

Used one for sale here - not sure if it fits a P6, you'll have to check - RANGE ROVER 3.5 Engine Oil Pickup Pipe V8 | eBay
 
quattro said:
I have just measured my 4.0L pistons at TDC and they are between 20.4ml and 20.9ml. If yours are 35cc with a 27cc head and composite gasket your CR works out at 8.15:1.

Can you bend the oil pick up back to shape?

Used one for sale here - not sure if it fits a P6, you'll have to check - RANGE ROVER 3.5 Engine Oil Pickup Pipe V8 | eBay
Click to expand...
I would be interested to know what the 4.0 piston dish measured on its own to confirm figures I have pls.
 
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