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Papay

Is this a 4K or 5K head?

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I'm getting ready to sort out the head gasket leak on the Papay van, so I acquired this head online.  It was advertised as a 5K, although I don't really know if I could spot the difference.  For what its worth, it has the same '100' casting as the head on my 5K engine right now.  

Have also ordered a Toyota head gasket, new head bolts, and other hardware in anticipation of the project. 

head1.jpg

head2.jpg

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It looks like a 5K head from the way the combustion chamber is indented around its edge.  I'll try to find a 4K pic for you.

OK, this is a stock 4K head, it is flat across the face, although dirty, so it looks like your head would if you skimmed 2mm off it. So I'd say yours is a 5K.

4K head.jpg

Edited by altezzaclub

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Great, that's the answer I was looking for.  I know there is some confusion about casting numbers and exterior bumps, so I wanted to be sure.  Any problem skimming a 0.5 to 1.0mm on a 5K?  I was thinking they already had 10.5:1 compression, does that sound right?  Will see how bad the water jacket corrosion is after it arrives I guess.  

 

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Nah, I doubt they have a van with compression over 9.5 to 1, but see if you can find out. The 5K is 15/13 times as big as a 4K, so the combustion chamber should be about 31ccX15/13= 36cc.  I think my 4K was about 31cc, I can't remember now, so you will need to buy a pipette & measure that figure to check it.

Pick the compression ratio you want, work out the area of the head surface with a little graph paper, and calculate how much to skim off to get the CR you want. Note the 4K has a heart-shaped combustion surface, yours will be a circle for the first couple of mm.

Your compression ratio is made up of the filling volume, (piston stroke volume)+(head gasket volume)+(combustion chamber volume) divided by the combusting volume, (head gasket volume)+(combustion chamber volume)

The maths method is..  (no guarantees here!)

piston area= (bore radius)X(bore radius)Xpi=4X4X3.14 =50.2SqCm

Piston stroke volume= 50.2X7.3 =366.7cc

Head gasket volume= 50.2X0.15 =7.5cc

So you are squishing 366.7 plus 7.5 plus say 36cc of head volume all into a combusting chamber of 36+7.5cc, and the compression ratio will be-

410/43.5= 9.4 to 1

If you want 10 to 1, reduce the combusting chamber volume to 41cc. Take off the 7.5cc the head gasket occupies and you need the actual combustion chamber to be 33.5cc, so take off 2.5cc.  If your head face is a circle of the bore, 50.2SqCm, reduce it by 2.5/50 or 0.5mm which is 20thou

In reality I expect you'll want to skim off around that figure, but you will have to measure the combustion chamber volumes and the head surface area.

CC head area.jpg

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These engines are quite popular where I live, and I'm betting the machine shop has a standard refurb sequence.  I'll to the initial cleanup on it and CC the chambers to see what I'm working with.  

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That's pretty handy, they will know all sorts of tricks & probably have cam grinds for it too.

Get hold of this manifold gasket-

https://www.rollaclub.com/board/topic/27374-one-piece-manifold-gasket-who-makes-them-4k/

and port the runners out to match, you might as well do what you can while the head is off.

Pull the block out and tip it over on its side then scrape all the rust and shit out of the waterways, especially around #4 cyl.  It sounds like its hot where you live and I"ll bet no-one has used coolant in it for years.

We had a 4K head skimmed last week for $80 I'm waiting to see what your costs!

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1 hour ago, altezzaclub said:

That's pretty handy, they will know all sorts of tricks & probably have cam grinds for it too.

Get hold of this manifold gasket-

https://www.rollaclub.com/board/topic/27374-one-piece-manifold-gasket-who-makes-them-4k/

and port the runners out to match, you might as well do what you can while the head is off.

Pull the block out and tip it over on its side then scrape all the rust and shit out of the waterways, especially around #4 cyl.  It sounds like its hot where you live and I"ll bet no-one has used coolant in it for years.

We had a 4K head skimmed last week for $80 I'm waiting to see what your costs!

Well I may not give them that much credit...this is Philippines, they are more aligned with doing it the cheapest way rather than the best way.  To give you an example, when I visited the machine shop to get a rough estimate, they assumed I would want to sleeve the block.   Why?  Because then I could use cheaper stock sized pistons.  I was like WTF?  Sleeving seems like a hell of a lot of work and I'm not sure I would trust the outcome.  Anyway, being judicious and making proper plans is where I am at the moment.  So sourcing some proper 81mm pistons is going to be part of this, but right now just focusing on the immediate need which is the head gasket, and hence the head itself.  Since I don't have much space to work, I find it wise to do all the necessary stuff on a separate head, then just swap it on.  Later I'll acquire a block and build it up with proper balancing and a healthy cam, etc.    

What is the particular advantage of the single piece gasket?  I was curious why the gaskets came split.  The single piece ones do look meatier.  Ive already acquired an extra dual plane exhaust mani and intake manifold, so the plan is to shave them down together and match ports as you suggest.  Getting a proper downpipe made might be a bit of a trick.  

Any recommendation for valve springs?  This won't be a race car, just thinking ahead. 

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nah- I picked a cam that would retain stock valve springs, I think over 0.4" lift is when they suggest new springs.

Bolting the inlet and exhaust manifolds together for the hot spot may have been the downfall of the two-piece gaskets, the different expansion may cause them to blow in the middle. It was just one of those things Toyota didn't get right.

Any flat-top 81mm pistons available?  I think your stock limits will be shallow-dish or deep-dish, which is another factor in compression ratios I forgot about. The dish in the piston affects the CR too, its part of the combustion chamber. So there must be two different 5K heads, one for each type of piston.

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3 hours ago, altezzaclub said:

nah- I picked a cam that would retain stock valve springs, I think over 0.4" lift is when they suggest new springs.

Bolting the inlet and exhaust manifolds together for the hot spot may have been the downfall of the two-piece gaskets, the different expansion may cause them to blow in the middle. It was just one of those things Toyota didn't get right.

Any flat-top 81mm pistons available?  I think your stock limits will be shallow-dish or deep-dish, which is another factor in compression ratios I forgot about. The dish in the piston affects the CR too, its part of the combustion chamber. So there must be two different 5K heads, one for each type of piston.

Supposedly 4age pistons and/or rods can work, but i'm going to have to do some careful research and math before buying anything.  

Speaking of the manifolds, has anyone on here experimented with making a phenolic spacer insulator between them?  I'm not interested in quick warmup, just reducing heat transfer.  

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8 minutes ago, Papay said:

Supposedly 4age pistons and/or rods can work.

Nope not even close.. the deck of the piston sits 3-3.5mm down the bore.

Whoever started that rumor years ago needs to be shot. 

 

I'll post about the rest when I get back from work. It will be long.

Edited by kickn5k

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Ok. The only real way to know if it's a 4k-u or 5k head is the lugs under the plug holes. I have never seen a 5k small bowl piston engine ever, so I cannot confirm or deny if they have lugs or not. I've seen a lot of inconsistencies with those casting numbers, so I personally don't worry too much about those.

I've personally had 2.25mm or .090thou decked of a 5k head recently and was no problem, in saying that though, you really need to match what you're taking off the head to what comes off the base circle of the camshaft. Well that's if you're keeping or have a hydraulic cam.  Valve clearance to piston(for those playing at home) is still plenty with a mid sized cam and the big dish piston.

 

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Head arrived yesterday, haven't had a chance to unpack it yet.  Went to look at a 5K short block today, still had 80.5 bores.  Probably will pick it up for about $140 AUS. 

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OK finally got around to removing the gasket and cleaning up the surface a bit.  Head shows previous repairs, JB-weld type repairs, around the corroded water jacket holes on #4 and a little bit on #3.  Surface seems to have never been skimmed.  When I was at the machine shop they were adding weld material to another 5K head, so it seems to be pretty standard procedure.  Its amazing how blocked the #4 passages were. 

head3.jpg

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The head came back for Louis' 4K. $40 to make it spotlessly clean, money well spent, and $80 to skim. Note how the mill leaves sharp clean edges everywhere, so there is no tendency for compression to tunnel out across the curved edge left by sandpaper.

cleaned head.jpg

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What's the recommended method for removing the whitish (calcium?) deposits all through the water passages?  Should I expect the machine shop to have a process for this, or need to soak it in something first, etc?

Also, I like the way they just welded up the holes around #2 there.

Edited by Papay

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