Turning A 3K Into A 5K?

[67Rolla-Ken]

Hi all,

 

I am planning to take the 5K out of 67Rolla and swap everything (except the sump) onto my spare 3K.

 

This is for 2 reasons:

Reason 1 - Then I don't have to go over pits (already registered with the 3K)

Reason 2 - The 3K block is tidy and in the original colour (I foolishly painted the 5K)

 

Will everything else swap over if I bore out the 3K to 5K diameter?.. Head, Drive shaft, lumpy cam, pistons, con-rods, oil pump??

 

Are they the same height??

[altezzaclub]

I don't think they are the same height. I thought the 5K was the same as a 4K, which is different to the 3K. Someone will now for sure.

 

Ah, no- Wiki says-

 

4K onwards have a 10mm higher deck height than 3K and earlier

 

Now you might not get the rocker geometry working. Your 5K is running hydrasulic tappets and the 3K will be solid. The setup is quite different. The 5K head would ahve to be used for compression ratio.

 

The 4K can be bored to 5K size if the walls are OK, but there might not be anything left of your 3K by then.

 

I don't think its going to work at all.

[67Rolla-Ken]

Thanks.

I have already changed the 5K to solid lifters. So if I used all the 5K gear except for the Con-rods (use 3K con-rods), would that work to counter the height diffrence??

 

 

Edit:

I found the conrod lengths:

3K = 113mm

5K = 120mm

 

That leaves me with 3mm to long a stroke... Any head give me the extra 3mm?

 

Or can you space the head from the block??

Edited May 10, 2013 by 67Rolla-Ken

[67Rolla-Ken]

New plan. Look for 110mm Long x 45mm Big end x 18mm small end con-rods :)

 

I have 2 3K engines I would like to do this to (mine and my cousins) so would be worth sorting the parts out.

[altezzaclub]

The easiest is to keep the 3K crank and rods and block, and bore it to 5K pistons. The stroke is the same but the bore makes a massive oversquare 80.5 by 66mm. This gives you a 1325cc motor

 

Then the problems are-

 

Will the 5 K piston rise to the correct height. You'll need the gudgeon pin to piston top heights. I think you might run into the 10mm deck height difference there.

 

Will the head give the correct compression ratio, depending on whether you have flat-top or dished 5K piston. You have a short stroke 5K now, only 66mm instead of 73mm, so to get compression up you would need to replace dished pistons with flat-tops, using the same 5K head.

[SLO-030]

Required things to put 5K internals into a 3K block is a follows;

 

1x Tub of Devcon

1x File

1x Die grinder with small carbide burr.

 

 

1) Apply Devcon over 5K eng. number.

 

2) File flat

 

3) Apply 3K eng. number

 

 

 

Been a while since I've had had a look at your build. But last time I looked, you were rebuilding the whole car. So it's got me a little bamboozled as to why original engine paint is so important, they generally look ratty as shit and are begging for a coat of jam.

 

 

(Disclaimer: I'm in no way suggesting committing the act of tampering with engine numbers ;) )

[philbey]

Ken, if you think that swapping all your internals to a clapped out 40 year old 3K block is easier than going through the pits and getting the 5K registered legitimately all I can say is...

 

....You're a mad bastard.

[Clapped out]

I don't think its going to work at all.

 

Your on the money, unless you have a lot of $ or time and patience, not to mention the clearance issues with the big end bearing caps hitting on the lower cylinder wall and the inside of the block by putting the 4/5k crank into the 3k block, cheaper to just do a 4a conversion or something.

Edited May 10, 2013 by Clapped out

[67Rolla-Ken]

Thanks all.

I think this plan is scrapped.

 

New plan: Take my 5K out and repaint the same colour as the 3K.

The colour thing was my main motivation, I know she'll have no problems going over pits.

[Redwarf]

5k crank won't swing in a 3k block. The big ends hit the sides.

[blown 5k]

5k crank won't swing in a 3k block. The big ends hit the sides.

 

This is doable with a little grinding.

[Redwarf]

Correct. You scallop the sides of the bores. Also the sump needs a bit of massaging too.

[67Rolla-Ken]

That all sounds a little beyond me. I think it will be much easier to make the 5k look stock.