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 RT Guide: Converting a 220 block to a 620 block 
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 Post subject: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 2:18 am 
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Summary

All rover T series engines share the same casting. I believe two different manufacturers were used (early castings can be identified by PET stamped on the bearing caps)

The T series blocks come in two base flavours, Naturally aspirated and Turbo. In essence the only difference between them is the tapping for the turbo oil feed on the front of the block, the later NASP castings actually having the hole already there, but blanked off.

However there are a number of modifications that were made to the engine block for fitment into a 600 Ti.

These were due to the different way the engine was mounted. While the 220 uses 3 mounts (a cambelt side mount, and front and rear engine mounts), the 600 only uses two, the cambelt side mount and the gearbox end mount.

In addition the 600 uses two stabiliser mounts to stop the engine rocking, an upper one located on the cambelt engine mount and a lower one which acts upon the aluminium sump.

Because of this there are two major differences in the design of the block fitted to the 600 when compared to the 200 or NASP.

The sump bolts on the 600 are increased from M6 to M8
The cambelt side engine mount bolts are increased from M8 to M10

The actual engines have other differences such as a different sump and wiring layout, with additional differences between wasted spark and early model distributor versions. In this guide we are only concerned with the physical differences of the bare block.

It is worth bearing this information in mind when swapping an engine from a 220 to a 600 or vice versa.

In this guide we will look at how to convert the 200 block to fit the 600.

Requirements

To do this job you will need:

  • Some form of drill press with suitable reach.
  • 8.5mm HSS drill
  • 6.75mm HSS drill
  • M8 HSS Taper Tap
  • M8 HSS Bottoming Tap
  • M10 HSS Taper Tap
  • M10 HSS Bottoming Tap
  • Magnet, Hoover, Compressed Air etc

You should make sure you use good quality taps and drills for the best fit.

Image

Procedure

It isn't strictly necessary to enlarge the sump bolts, as the M6 bolts can be used with copious amounts of sealant to make up for the oversize holes in the gasket. However it should be noted the bolts were enlarged for a good reason to take into account the extra stress on the sump.


The procedure for converting the block is very basic.

Simply drill and tap the M6 sump holes to M8 using the 6.75mm drill and tapping the holes square, first with the taper tap, and running through with the bottoming tap. Then repeat the procedure with the M10 engine mount bolts. There are however a number of caveats.

1: The block is made of cast iron, and is therefore easy to machine, however it "dusts" easily and will clog taps very quickly. You should ensure that you blow/hoover the dust and back the tap off more frequently than you would normally do.

2: It goes without saying that machining your engine block is not a task to be undertaken lightly as there is zero room for error. If you are not experienced or confident completing engineering tasks then you should seek a professional shop to undertake the work.

3: Tapping and drilling produces a lot of swarf which you need to avoid putting inside your engine!

Sump bolts

As the sump bolts are straight through holes and external to the engine the danger of swarf being ingested into the engine is minimal. These could be drilled carefully with a hand drill, however if at all possible a pillar drill should be used to ensure the holes are accurate and not oversized.

Engine mounting bolts

The engine mounts are different between the 200 and the 600 and you will need the bolts and mount for the 600, which will consist of 5x 25mm M10 10.9 grade and 1x 55mm M10 10.9 grade.

The mount looks like this:


Image


This bolts to the block and is sealed in place using a good quality RTV - here is a comparison of the blocks:

220 Block (M8 holes)
Image

600 Block (M10 holes)
Image

The first stage is to clean all the bolts you will use for the mount, otherwise they will bind in the holes. Run them quickly through a M10x1.5 die.


Image


You will need to jury rig a pillar drill to enlarge the existing M8 holes in the block to M10, it is not possible to do this accurately by hand.


Image


Drill the holes at around 900rpm with a very slow feed, you want to generate small chips of metal. Ensure the drill is securely mounted and not able to move, these holes must be 100% accurate!

Use a depth stop to ensure you do not drill down any further than the bottom of the existing holes. Note that all but two of the holes are blind. The holes in the 12 and 6 o'clock positions are straight through (12 o'clock is the topmost bolt to the head). When tapping and drilling these avoid swarf falling into the water jacket of the block.

Start with a taper tap, keeping it square to the block to start the thread. Tap the metal dry with frequent clearing of the tap. You can use a little WD40 if you are not happy tapping dry.


Image


Finish with a bottoming tap to extend the thread to the bottom of the hole. Ensure that the hole is deep enough for the bolt to clamp the mount with no trouble.


Image


I found a powerful magnet acting through a small blade screwdriver was a effective way to remove most of the swarf cleanly from the holes, finishing off with either a hoover or a air blow gun.


Image

Image


Ensure thread is spotless before switching to the bottoming tap, or before running the bolt into the hole.

Warning!

The hole in the 11 o'clock position breaks through into the oil return gallery. When drilling and tapping this hole swarf will collect inside this gallery and in the head or the sump as a result.

I found attaching a hoover via the coreplug helped avoid the worst of it, however there was still residue so this procedure is best done with the sump and head removed to ensure the swarf can be cleared. It is also not necessary to tap this hole as deeply as the others as the mount is raised slightly for this bolt.



Image


Clean the threads and oil with WD40, test fit the bolt and mounts, the bolts should be a snug fit in the holes.


Image

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 Post subject: Re: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 7:21 am 
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very good, clear post. id use some cutting fluid if you can, saves killing the drill / tap.

Drew


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 Post subject: Re: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 7:46 am 
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how come when my ti blew up i replaced the bottom end with a 220 lump and i never had to do this?

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 Post subject: Re: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 8:53 am 
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Thanks Drew, I think there are special cast iron cutting fluids available to extend tool life, but all the advice I could find was related to dry tapping. I figured as there are only 6 holes on the engine mount it made no odds.

Pucc, I don't know! I checked a number of blocks before I put together the guide and did some searching on here for an answer, as I didn't realise myself. All the 220 blocks had M8 mounts and I have stripped three 600 engines and they all had M10s. Did you swap over the camside engine mount at all?

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 Post subject: Re: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 10:00 am 
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The 220 engines only have 3 mounts Jon , the gearbox mount was never present.

Regarding the cutting fluid, Cast iron is self lubricating and you dont really need any lube for it, not saying some specialist stuff wont help , just not strictly needed.

I just wished you had swapped my ti block for your 220 before you did all this :lol:

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 Post subject: Re: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 11:21 am 
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Thanks Dan, I have ammended it :D

I kinda wish I had started off with a Ti block as well. :| Still you live and learn, hopefully this will help somebody else avoid the mistake of assuming they are the same!

Can you update the guide on reverse fitting - i.e. Ti block into a 220? I would guess you would have to enlarge the holes in the sump gasket and sump, and the holes in the engine mount and source new 10.9 rated M10 bolts. :?

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 Post subject: Re: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 11:43 am 
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The way i have done it.

Open the holes up in the cam side mount from M8 to M10 to bolt to the Ti block.
Remove the coil mount from adaptor plate and fit rear engine mounting bracket.

Sump ive always left the ti one on as its 10mm more shallow , but it doesnt house the pas pipes nicely. My next one i will use m8 - m6 step down threads and fit the 220 sump that way :)

Enlarging the sump gasket holes isnt a possibility as they have brass washers in there :(

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 Post subject: Re: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 1:57 pm 
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Would the Ti gasket not fit? Then just drill out the holes in the sump.

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 Post subject: Re: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 1:59 pm 
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Nope , sumps a totally different shape , and so is the gasket :(

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 Post subject: Re: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 4:59 pm 
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i have an alloy sump from my ti on my 220 block... i just used different bolts as the ti ones are too thin...as for the gasket i think i used a 220 one...

i did how ever change the side engine mount but as far as i can remember it was a straight swap as far as nuts go..

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 Post subject: Re: RT Guide: Converting a 220 block to a 620 block
PostPosted: Tue Jul 28, 2009 5:07 pm 
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Ti sump will fit a 220 block , as the holes are bigger, you had 1mm of play either side though :)

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