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LT 2.4 Petrol engine to 2.5 TDI conversion

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cnycl View Drop Down
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    Posted: 05 Dec 10 at 22:06
Finally our TDI conversion started progressing and I'll post it here step by step as my syncro friends (www.syncroturk.org) complete each level (wiring, sump modification, exhaust fitment, electrics, engine installation etc.). I hope this may help others deciding the same upgrade since we know this has been done before but there's no clear guide on how to do it properly.

As usual, disclaimer conditions apply; this conversion is something we're doing on our own risk and we can't guarantee it will function properly on your vehicle or you can get legal permits for road use and it is not approved by the vehicle manufacturer. Therefore if you're thinking of doing the same conversion, don't forget you'll be doing it on your own risk, knowing the conditions mentioned above.

Anyway the vehicle we're working on is an '88 VW LT 31 with 2.4l carbed petrol engine mated to a 5 speed gearbox.  Donor vehicle is an Audi A6 with 5 pot 2.5l TDI engine.

This is the beginning, engine and wiring loom as they come from the breakers.



Wiring loom sorted and simplified.



2.4l turbo diesel LT sump and TDI sump side by side. Engine bracket on LT requires LT specific sump to be used on TDI engine since TDI sump is much deeper than the LT one. Bolt pattern of these sumps are very very smiliar except 2.4l sump is a little longer (1 pot) than 2.5 TDI. 



Long portion to be cut  is marked as below



And there it goes



Cut but unwelded part on the engine. Since depth is not uniform along the sump minor leveling is required before welding. 



LT sump on TDI engine. We did not modifiy the oil pick up pipe yet.



Another angle



More to come as the project keeps going...




 


Edited by cnycl - 06 Dec 10 at 10:05
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GT500 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Dec 10 at 09:34
Great stuff!!!!
Just stripping my A6 at the mo! Try to catch up with ya!

Wiring, is a pain. been stripping my loom back (its still in the car) testing as I go. Seems the immobiliser is a bit cleverer than I thought. Trying to find the current flow diagram for it... Anyway it did run lovley now it its stopped by the dammed immo. I have vagcom and all you get is "start blocked"
Going to get the engine out today and sort it when its in the van.

ANy chance we can have a detailed few pics of your loom please?

Rob
Rob... The only LT on 18" wheels.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bo_Hedin Quote  Post ReplyReply Direct Link To This Post Posted: 10 Dec 10 at 20:00
Wow, Just what we've all been waiting to see.
Good luck!
Starting to think along these lines as I can't even get an oil filter for my engine anymore....and that extra performance would be great.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Canada LT28 Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 10 at 22:52
Excellent work Cnycl,
I've got my 99 TDI 1.9 and am looking to go with the mech TDI pump to do away with the electronics. Looks like you will be done long before I actually get started.

Mike
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mechano Quote  Post ReplyReply Direct Link To This Post Posted: 12 Dec 10 at 19:10
Hi All,

This is Eren, I am actually a syncronaut and not an LT fan, but as Cnycl stated this conversion is done in my garage and mainly by me.

So here is what we did this weekend with Can (cnycl):
Took out the engine from the LT (what a pain in the a..) also the transmission.




with both engines out, we were able to see what will or will not fit.

-The bellhousing pattern is same as TDI as expected,




I am planning to use the TDI flywheel, pressure plate & starter, as the TDI has much more torque.
-TDI has a 240mm clutch whereas the 6cyl petrol has 228mm, TDI also has a dual-mass flywheel.
-TDI friction disc has the same spline as the 6cyl petrol so it can be used
-The pilot bearing in the TDI flywheel is smaller and 6cyl petrol engine has a bearing pushed into the crankshaft with a bigger inside diameter. 
I was able to push out the bearing of the TDI flywheel, so installing a new bearing in to the TDI crankshaft will solve the problem.

-However there is problem: When assembled, the TDI pressure plate will sit approximately 1cm out than the 6cyl petrol one. This means that the throw-out bearing will be pushed 1cm in to the transmission. I guess the clutch adjustment will not be enough to solve this problem, so I am planning to modify the lever of the clutch or may be its fulcrum or use another pressure plate...

Looking at the other sides of engines:

-The engine mounts are completely different, 6cyl ones wont fit to TDI, both sides need to be build from scratch.
-The crankshaft pulley also the visco fan of the 6cyl petrol will fit to TDI engine.
-The LT power steering pump fits to TDI engine with very little grinding of its bracket.
-The alternator will not fit as it simply hits the turbo, has to be relocated and looks like a bit hard to find a new place...

As for the wiring I have not finished it yet, as Can (cnycl) sent the pictures I have simplified it but I have to take out the wiring of the pedals from the main harness. I am not worried about the wiring as I have converted my syncro to TDI before (1.9 AFN engine)

A syncro friend I met in Germany in syncro25yrs event sent the wiring diagram of this engine, here is the link: http://www.audifans.net/ftopict-33526-aat.html+wiring



Here we are pulling the engine-less LT away from the garage with my syncro, we had some nice snow this weekend here in Ankara / Turkey.

I will be working on this conversion only weekends, so this will take some loooong time.. we'll see..

Eren B.




Edited by mechano - 16 Jan 11 at 21:49
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Canada LT28 Quote  Post ReplyReply Direct Link To This Post Posted: 12 Dec 10 at 21:05
Can you tell how the shift linkage for the tranny looks? Will it be an easy changeover to the stock LT shifter? Also, do you think a 1.9 tdi would also need the sump cut and re-welded?

Good work.....

Mike 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cnycl Quote  Post ReplyReply Direct Link To This Post Posted: 13 Dec 10 at 21:39
Hi Mike,

Since we're using the original tranny, stock LT shifter configuration will remain intact. So no worries there. 
Regarding 1.9 tdi sump, Mechano knows it better. He's done a similar engine conversion (2.0l petrol to 1.9 tdi) on his syncro before. 
But as far as I know/saw desing of the front axle of LT will probably require any other sump to be modified somehow. 
To keep the engine hump low inside the van, VW engineers stuck everything really close in the engine department.

Good luck


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Canada LT28 Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 10 at 00:45
You are changing out a gasser for the TDI and I think the tranny has the same gear ratios as the diesel LT. Do you know what the difference in RPM is for the two engines. There was a Volvo sitting for a few years behind my shop and just when I was going to ask the owner for it, he towed it away. Gear ratios would have been nice but now I must find something else. Is the top end RPM better on the TDI over the 6 pot?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cnycl Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 10 at 07:44
Gear ratios of the current gearbox will not probably match TDI engine but  we swapped wheels and tyres from 14"/195-80 to 16"/205-80 and this may help a little bit. 
In the long run I think it's better to use a different rear axle than playing with the gear box. Especially an axle with a diff lock.
Calculations for rear axles with different ratios and wheel sizes are given below (these are 5th gear calculations).
If you're staying in 100-120 km/h band at 3000 rpm in 5th gear, TDI engine has more than enough pull to handle other gears and long distance rides will probably be much more comfortable.
BTW your stock axle gear ratio may not be 40:9 and transmission ratios may differ please take this into account when making modifications.
 
Transmission        
1 2 3 4 5
6,17 3,23 1,84 1,27 1
 
  Speed Km/H
  195/80 R14 205/80 R16
RPM 40:9 Stock 46:13 Dana 41:11 Dana 40:9 Stock 46:13 Dana 41:11 Dana
1000 26,90 35,56 33,76 29,59 39,12 37,14
1500 40,35 53,35 50,64 44,38 58,68 55,71
2000 53,80 71,13 67,53 59,18 78,25 74,28
2500 67,25 88,91 84,41 73,97 97,81 92,85
3000 80,70 106,69 101,29 88,77 117,37 111,42
3500 94,14 124,47 118,17 103,56 136,93 129,99
4000 107,59 142,26 135,05 118,36 156,49 148,56
4500 121,04 160,04 151,93 133,15 176,05 167,13
5000 134,49 177,82 168,81 147,95 195,61 185,70
5500 147,94 195,60 185,69 162,74 215,17 204,27
 


Edited by cnycl - 14 Dec 10 at 07:45
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Canada LT28 Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 10 at 11:27
Pretty informativeThumbs Up. I understand the stock numbers but is the "Dana" from a TDI truck? I am pretty sure I have the stock ratios with the 40:1 diff as I need a strong tailwind and a good down hill to get past 110km/h. I did change to 175/16 wheels (thread somewhere on here) which dropped the rpm a bit but it's not a huge improvement.

If it is available I may ship one over, or am I nutsConfused.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote cnycl Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 10 at 13:04
Dana axle is not from a TDI engine.
They're stock axles of most U.S. branded 4x4's, pick up trucks etc.
We're planning to get a set from the breakers to convert 4x2 LT into 4x4 but thats another story.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mechano Quote  Post ReplyReply Direct Link To This Post Posted: 17 Dec 10 at 08:49
Hi,

I guess you need to use an LT sump and cut-weld like I did as any other sump will hit the front-end.

For a 1,9 swap you need use an adapter plate between the engine and tranny as the 1,9 4cyl bolt pattern is not the same as the 5 or 6cyl ones.

When you use an adapter plate the engine will move forward which may cause even the LT sump to hit the front end, have to check.

Eren B.

Originally posted by Canada LT28 Canada LT28 wrote:

Can you tell how the shift linkage for the tranny looks? Will it be an easy changeover to the stock LT shifter? Also, do you think a 1.9 tdi would also need the sump cut and re-welded?

Good work.....

Mike 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Canada LT28 Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 10 at 11:04
Thanks Eren,
Have you already put a 1.9 in an LT? I won't get to this before summer but it is always good to know what i am up against.

 Keep up the good work....Smile

Mike 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mechano Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 10 at 11:25
Hi,

No. 
I did convert my T3 syncro from wasser-boxer to 16 valve petrol and then to 1,9 TDI which also involved to build an adapter-plate and flywheel to covert boxer bolt pattern to inline 4.

Definitely a 5cyl Diesel conversion for LT is easier than a 4cyl, as you won't need an adapter-plate. 

Thanks.

Eren B.



Originally posted by Canada LT28 Canada LT28 wrote:

Thanks Eren,
Have you already put a 1.9 in an LT? I won't get to this before summer but it is always good to know what i am up against.

 Keep up the good work....Smile

Mike 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mechano Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jan 11 at 21:16
Hi All,

It's been a while, it was Christmas holiday, also I was busy at work (moved to another office etc.)

Anyway, this weekend I checked engine mounts, I decided to use and modify the LT aluminium mounts. On either side only one hole location is same on TDI engine as the petrol.

Turbo Side:

This is how the 2,5 TDI (AAT code) engine looks like on turbo side 

This is how the LT petrol engine looks like, same side



The LT oil filter adapter has to be used on TDI engine as If you try to use the TDI's original, the filter will simply hit the engine cross member (front-end).

This is how it looked like when I have put the LT filter adapter and LT engine mount on TDI engine:


I had to remove the turbo oil return pipe as it would hit the filter bracket. I will make a new pipe to oil sump.

I had to grind the mount to clear the turbo itself, also as you can see only one bolt is holding the mount on engine, but as this hole is at correct location so the engine mount location is correct here.

Here you can see the the area that I have grind to clear the turbo:




I decided to use the hole at the left side of the mount seen above as the second bolt location. So as to do it I have cut these parts:



and have them welded as my TIG welder is DC and wont weld aluminium:




 
as for the third bolt, I decided to make a steel part that would bolt on the engine itself where the oil return flange was. It has two M8 bolts. I have designed that simple part which would go between the aluminium mount and engine block:



this part will fit here:



I decided to have the part laser cut, I have ordered it and will collect it tuesday.

For the other side of the engine, again only one bolt is at the same location and can be used.
I have grind the mount a little bit to fit it on the TDI engine:



Also I had to cut the dipstick tube of the TDI, no problem as the LT dipstick tube is on the oilpan.



I will cut an aluminium part and weld it on the mount to use the other near holes for bolting.

Here is a sketch: (yellow lines)


All photos can be seen here:



Edited by mechano - 16 Jan 11 at 21:51
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alevaro Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jan 11 at 16:45

cnycl

Excellent work! 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote cnycl Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jan 11 at 21:35
Originally posted by Alevaro Alevaro wrote:

cnycl

Excellent work! 


Thanks but compliments go to Mechano he's the one struggling with TDI engine in freezing cold weather.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote mechano Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jan 11 at 19:28
A little update:

I finished the turbo side engine mount.
Here is the steel part I made which goes between the engine block and the aluminium mount:



This is how it looks like when the oil filter is in place:



Also I started working on the other side,
I have cut an 8mm thick Aluminium sheet to weld to mount as I have sketched before:







slowly...

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Post Options Post Options   Thanks (0) Thanks(0)   Quote GT500 Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jan 11 at 01:02
Looking very nice!
Great help to me.. I think i'm going to get a spare engine from the LT I'm breaking.. need to have mine off the road as little as possible.
Stripped the A6 and are slowly going through the rats nest of a wiring loom.. Very boring!
Rob... The only LT on 18" wheels.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Canada LT28 Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jan 11 at 12:42
Hi Guys,

Eren, regarding the 1.9tdi, I will be cutting the prop shaft back to either put in a laycock overdrive (if i can find one at a reasonable cost) or a friend has a BMW 318 tranny that we are looking at putting in. Either way, Can I make the engine placement back far enough to still fit in and also miss the front end?
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