Engine rebuild

Engine rebuild

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Discussion

IMI A

6,779 posts

145 months

Monday 12th August
quotequote all
4321go said:
So, onto the machining of the block.

You’ll recall that the bores were badly scored by the ceramic “sand” that had worked its way back up the header pipes from the cats:



As standard, the bores of the cast alloy blocks are plated with Nikasil, a nickel/ceramic coating that provides a hard finish for the piston rings to run against. Boring and re-plating/honing would result in oversize bores, and oversize pistons aren’t available. So the options were a new block, or a sleeved one. The latter would be a £2k saving and would result in a harder-wearing finish. There were no obvious advantages to having a new block for me, so we decided to machine the old one.

The steel liners came from L.A. Sleeve of Santa Fe, Ca. and are flanged. That is to say that for most of their length, they are a thin-walled steel tube, but towards the top, cylinder head-end, they are much thicker-walled. Therefore they are much more positively seated than a sleeve without a flange. The bores are rebored to the outside diameter of the sleeve, and then counter-bored to the diameter and depth of the flange, before the deck is skimmed flat. With the head torqued down the flange is pressed firmly into its seat. This isn’t my block, nor L.A. Sleeve liners, but I’m sure mine looked very similar:



In the following pictures it appears that the bores have become Siamesed, and indeed they have, but only to the depth of the flange. Lower down, the alloy webs remain between the cylinders (and this IS my block):





Lower down in the bores, the liners have “windage” holes drilled through them, and this is a convenient time to show you one of the numerous differences between the 5.0 and 5.2 litre blocks. (Remember that the two V10 units (Lambo’s 5 and Audi’s 5.2) were developed separately from related, but different, 4 and 4.2 litre V8s.)

Here is an end shot of a (later) 5.2 litre block:



And my (earlier) 5.0 litre block



Note the two extra holes in the earlier block. These are the windage holes and pass through the lower end of each cylinder for the entire length of each bank. As the pistons thrash up and down, the air in the volumes below them is repeatedly being compressed and expanded. In the earlier engine, these pressure changes are alleviated and reduced by the air being allowed to pass from one bore to the next through the windage holes (in addition to it passing under the base of each bore). This extra alleviation of the pressure changes wasn’t needed in the later engines due to the increased efficiency of the oil scavenge pump fitted to the latter. Of much greater power (six chambers rather than three?) it can pump oil from the dry sump back to the oil tank at a much greater rate. Therefore the oil is less likely to become aerated in the short time that it spends under the thrashing pistons, and so there is less need to reduce the air pressure differences with the later oil pump.

Who knew? (Well, Ricky for one!)

Anyway, here is one of the windage holes in a cylinder sleeve, as seen down one of the bores of my block:



(I should add that all of the shots of my block were taken shortly after it arrived back from the machinist. Ricky had been measuring up for the crank shell sizes and then it was going into his parts cleaning tank for several hours. That should have shifted not only the swarf in the galleries, but the dead flies too!!)

With the sleeves machined into place, they then have to be honed to size and shape. And it was this process that led to the biggest delay in the machining process. Because, in all of the photos of my block above, the bore is the wrong shape!!

When you torque down the cylinder head onto the block, it distorts the block itself. (And indeed, how the block is distorted depends on whether the head is held down by studs or bolts, the former squashing the top of the block, the latter the bottom.) As you look at the photos above, the bores are not round! They will only become so again when the cylinder heads are torqued down onto them. Therefore, before the cylinder liners can be honed to size, the block has to be distorted in exactly the same way as if the heads were in place and torqued down.

This is achieved by the use of “Torque Plates”. These are THICK metal plates that are bolted down onto the block in exactly the same way as the cylinder heads are (either studs or bolts) and to the same torque, but with large holes in them allowing the honing tool to pass through them. The machinists “had” them, but couldn’t find them! Ricky has his own, but they were apparently too deep for the machine shop. So they had to make up a new set.......

Here’s a picture of a bore being honed (again, not my engine). The torque plate is a thick metal plate, but not as thick as the actual cylinder head casting. So here extension tubes have been machined to allow the actual head studs to be used. The honing tool is four abrasive pads held against the cylinder walls by spring pressure:



Next time......... Con rods!! (Trust me; it’s genuinely interesting!!)

Edited by 4321go on Sunday 11th August 21:44
Porn!

Dr G

13,725 posts

186 months

Monday 12th August
quotequote all
Really nice to see this marching on and eagerly awaiting more updates. Really interesting stuff.

4321go

Original Poster:

480 posts

131 months

Monday 12th August
quotequote all
Thanks chaps!

So firstly, how do you make a connecting rod?:

Cast/forge/sinter your rod. Machine the hole in the little end and press in your bushing. Drill your two holes in the big end for the con-rod bolts. Maybe tap these holes too. Now cut the big end in half. The hole for your crank pin will no longer be round, but this isn’t really very important at this stage. Take the rod and it’s end cap and machine their mating surfaces to accept a collet to ensure that when they are joined together, there is no possibility of the two pieces moving relative to one another. Now join them back together and torque-up the con rod bolts. Finally, machine the big-end hole to the correct, round size.

Here’s the finished big end of a connecting rod. It happens to be a CP Carrillo rod for a 5.2 litre, forced induction build of Ricky’s:



I had the choice of Carrillo rods to match the pistons (circa £2800 IIRC) or OEM Audi rods (£1100). The Carrillo rods are perfectly machined things of beauty and it was tempting to spend the extra. But my engine doesn’t need them. They’re a must to contain the extreme forces generated by forced induction; a supercharger or twin-turbo conversion. But the Audi rods are easily good enough for my (relatively) standard build. Besides, the Audi rods are considerably lighter. As are the CP Carrillo gudgeon pins to suit. For forced induction engines, they produce a machine-steel pin, with massively thick walls and a narrow hole down the centre. For a NA engine, we’re still using Carrillo gudgeon pins because we’re using Carrillo pistons, but they’re of a similar wall thickness as the OEM Audi pins. So we’re using the lightest piston/gudgeon pin/con-rod combination available. Good-oh!

But onto those Audi connecting rods. What’s missing from this picture?



That’s right! There’s apparently no break in the big end!! How the hell do you install the bearing shells and clamp it around the crank pin?

And here’s where the economies of scale between an OE manufacturer and an aftermarket manufacturer show. CP Carrillo have to manufacture their rods in something like the fashion that I described above, although I probably missed out several hardening and machining steps. The Audi rods, in comparison, are “cracked”!

Their manufacturing process reads something like this:

Forge rod. Machine little end and press in bush. Drill and tap big end for the con-rod bolts and install said bolts. Machine hole for crank pin in big end. FREEZE the whole rod in liquid nitrogen. Hit with lump hammer.........

Yup, in that photo above, the big end is cracked in half at a crystalline level! And until you undo the con-rod bolts for the first time, you’ll never see the break. And when you’ve fitted the bearing shells and come to join the two halves back together again, they marry perfectly. Every time. And the mating faces can’t possible move relative to one another. So the big-end hole will be perfectly aligned. Every time!

I know! Genius, isn’t it!!!

Here are some shots of one of my rods that has been undone:





And here are the two end caps; CP Carrillo (with its machined-in collets) in the foreground, the unique crystalline face of the Audi “cracked rod” in the background:



And the rod married whole again. Torque-up the con-rod bolts (they haven’t been here) and that visible crack will be all-but invisible again:



Mind blowing!

Trev450

5,751 posts

116 months

Monday 12th August
quotequote all
Another highly informative update. Very pleased to hear that progress is being made.

RumbleOfThunder

2,825 posts

147 months

Monday 12th August
quotequote all
That IS very interesting. I didn't know that was done for con rods. Seems to work on the same principle of this.

https://www.youtube.com/watch?v=KqVydQ6EdDg&fr...

Larry5.2

361 posts

52 months

Tuesday 13th August
quotequote all
Wow!! Incredibly informative thread - thanks for taking time to post everything up!

wilksy61

154 posts

60 months

Here’s a picture of a bore being honed (again, not my engine). The torque plate is a thick metal plate, but not as thick as the actual cylinder head casting. So here extension tubes have been machined to allow the actual head studs to be used. The honing tool is four abrasive pads held against the cylinder walls by spring pressure:

Very interesting reading about this rebuild, however could I just make a point regarding the honing process and in particular to the pads being held by spring pressure.

They are held against the bore by pressure exerted from the head mechanism if they were held by spring pressure then they would follow what ever shape the hole is. This is why those cheap crappy hone tools sold on eBay etc are useless.

I used to work as an application engineer for Delapena Honing many years ago


Megaflow

6,725 posts

169 months

4321go said:
Thanks chaps!

So firstly, how do you make a connecting rod?:

Cast/forge/sinter your rod. Machine the hole in the little end and press in your bushing. Drill your two holes in the big end for the con-rod bolts. Maybe tap these holes too. Now cut the big end in half. The hole for your crank pin will no longer be round, but this isn’t really very important at this stage. Take the rod and it’s end cap and machine their mating surfaces to accept a collet to ensure that when they are joined together, there is no possibility of the two pieces moving relative to one another. Now join them back together and torque-up the con rod bolts. Finally, machine the big-end hole to the correct, round size.

Here’s the finished big end of a connecting rod. It happens to be a CP Carrillo rod for a 5.2 litre, forced induction build of Ricky’s:



I had the choice of Carrillo rods to match the pistons (circa £2800 IIRC) or OEM Audi rods (£1100). The Carrillo rods are perfectly machined things of beauty and it was tempting to spend the extra. But my engine doesn’t need them. They’re a must to contain the extreme forces generated by forced induction; a supercharger or twin-turbo conversion. But the Audi rods are easily good enough for my (relatively) standard build. Besides, the Audi rods are considerably lighter. As are the CP Carrillo gudgeon pins to suit. For forced induction engines, they produce a machine-steel pin, with massively thick walls and a narrow hole down the centre. For a NA engine, we’re still using Carrillo gudgeon pins because we’re using Carrillo pistons, but they’re of a similar wall thickness as the OEM Audi pins. So we’re using the lightest piston/gudgeon pin/con-rod combination available. Good-oh!

But onto those Audi connecting rods. What’s missing from this picture?



That’s right! There’s apparently no break in the big end!! How the hell do you install the bearing shells and clamp it around the crank pin?

And here’s where the economies of scale between an OE manufacturer and an aftermarket manufacturer show. CP Carrillo have to manufacture their rods in something like the fashion that I described above, although I probably missed out several hardening and machining steps. The Audi rods, in comparison, are “cracked”!

Their manufacturing process reads something like this:

Forge rod. Machine little end and press in bush. Drill and tap big end for the con-rod bolts and install said bolts. Machine hole for crank pin in big end. FREEZE the whole rod in liquid nitrogen. Hit with lump hammer.........

Yup, in that photo above, the big end is cracked in half at a crystalline level! And until you undo the con-rod bolts for the first time, you’ll never see the break. And when you’ve fitted the bearing shells and come to join the two halves back together again, they marry perfectly. Every time. And the mating faces can’t possible move relative to one another. So the big-end hole will be perfectly aligned. Every time!

I know! Genius, isn’t it!!!

Here are some shots of one of my rods that has been undone:





And here are the two end caps; CP Carrillo (with its machined-in collets) in the foreground, the unique crystalline face of the Audi “cracked rod” in the background:



And the rod married whole again. Torque-up the con-rod bolts (they haven’t been here) and that visible crack will be all-but invisible again:



Mind blowing!
Known as fracture split rods. There are now a few engines out there with fracture split main bearing caps as well.

4321go

Original Poster:

480 posts

131 months

wilksy61 said:
however could I just make a point regarding the honing process
I’m an airline pilot. Whilst I can attack an old-tech British Classic with a spanner, there’s absolutely NO guarantee that it won’t result in a stripped thread!!

I positively welcome being corrected and would encourage contributions from the experts as we go along.....

thecook101

630 posts

59 months

That's brilliant. Thanks for posting, never knew about that. If I had taken that apart I would have thought fk, I've broken the bloody thing! biggrin

wilksy61

154 posts

60 months

4321go said:
I’m an airline pilot. Whilst I can attack an old-tech British Classic with a spanner, there’s absolutely NO guarantee that it won’t result in a stripped thread!!

I positively welcome being corrected and would encourage contributions from the experts as we go along.....
Cheers, you should see how they hone con rods due to the of area for a stone to correctly work on, and also can attack British Classics with a spanner and, depending how long they have been left outside, will almost certainly result in many stripped threads