Engine rebuild and power mods

[makeitfit]

Old dog, new tricks

Today I have been mainly learning to time the cam
Having spent hours on youtube, burton cam site, Luke's advice and general jibber jabber , I went for it.
First off the tear down turned out to be a blessing in disguise. I set the basic static timing according to Nissan but ofcourse with this hi-lift re-profiled cam , it was wrong.
Here's what I found as soon as the head was off, valves been playing kiss chase with the pistons

Secondly the exhaust manifold was puffing a bit. I did try tightening the nuts when warm etc but no help. Here's why, the ruddy things are blown to bits .

I had the manifold checked and it turns out to be well pissed, something I'm working on myself as it happens :lol

Here's the revived manifold
More machine time

So here I am again in the deep end about to re-time the cam

Had to drop the oil as sump exposed again, but it needed doing anyway as there was some water contamination.

Now here's the fun bit :sly I went on that there tinterweb and found a " build your own timing disc" kinda site. Made this from the cam figures. Found the wife's laminator and bosh, job's a good'n

Armed with dial gauge, beer and some old wiper blade inner, I set about some brain strain . First off using all the info kindly shared I got the true TDC sorted .

Since then, I went on to the cam timing as Luke suggested and think I've got a result. Got a bit late but it seems from experimenting that one cog tooth equates to 8 degrees of cam timing . Which is handy as I calculated the cam to be out by 9 degrees.
I'll be back on it with fresh head in the morning to confirm that, but it looks promising at the mo.
I'll also be doing a dummy build and playing with some playdo :naughty
Onwards

 

[solarman216]

Careful Pete as from your pics looks like both valves have been touching piston, if so you need to be looking at head gasket thickness, Rick

 

[makeitfit]

Careful Pete as from your pics looks like both valves have been touching piston, if so you need to be looking at head gasket thickness, Rick

Yes I saw that too. I'm thinking I set clearances the same all round and obviously not accurate enough either. That's why I'll be playing with plastacine tomorrow, just to check.
I'll measure old and new head gaskets too.
Worst case I'll need to shorten the pushrods

 

[solarman216]

Oops "shorten the push rods" not a good idea, the lift will remain the same, you can only get round it by thickening the gasket or having larger than normal valve clearances, but as both valves been kissing you cannot alter the timing as one valve will hit harder than it does now, the fact both are just touching says timing is best you can get, Rick

 

[solarman216]

It is a good while since I did a 2.7 gasket but seem to remember they came in three thicknesses one notch, two and three notches, did you check yours? and also you have had it skimmed yes? so need to compensate for that, Rick

 

[makeitfit]

Oops "shorten the push rods" not a good idea, the lift will remain the same, you can only get round it by thickening the gasket or having larger than normal valve clearances, but as both valves been kissing you cannot alter the timing as one valve will hit harder than it does now, the fact both are just touching says timing is best you can get, Rick

Damn it you're right again :doh
The cam timing though does work out at 109 degrees ATDC . IF I understood the method correctly, the stock Nissan set up puts this cam at 118 ATDC
Hence my plan to play playdo and check the new valve/piston clearance.
As you say it may end up being bigger valve clearances.
I haven't checked HG thicknesses yet by the way.

 

[solarman216]

Think you may well end up with clacking tappets at great annoyance to the neighbours,, Rick

 

[solarman216]

You need to remember that on these engines on the up stroke the piston follows the exhaust valve by a few thou, and on the down stroke the inlet valve follows the piston by a similar few thou, alter the timing for best breathing and engine is no more, , Rick

 

[Davey Boy]

Hey you two....
This is bloody good deep surgery stuff.
Thanks for sharing! :thumb2

 

[makeitfit]

Spent many hours trying to get my head round this here cam timing. Went at it yesterday with clear head.
First off I followed the highest lift method to try and time the cam. Did it time and time again lol but consistently got about 102 degrees. It should be 109.

So my little brain and decided to experiment and found moving the cam cog one tooth got me 8 degrees as best I could tell.

Now on 109 degrees my roll soon ended. I did a dummy build with the new HG . Incidently the old gasket was 1.65mm and new one 2mm
I put 2 blobs of play doh on the cylinder to check valve to piston clearance.
Set the valve clearance at a generous .3 and turned the crank. Round and round and thunk, bugger. Solid stop
Start again grrr, this time in stock timing . Repeat the plasticine blob. This time I have valve room , yay.

It was yellow but mucky hands haha
Now as Rick has been proved right again I ask the following. Will I be better off getting cam Hi lift reduced a bit so I can take advantage of the cam properly?
I have a bunch of pump mods to do which will bring more fuel for low down power and an earlier boost .
Onwards :naughty

 

[solarman216]

It is not so much the high lift that is the problem but attack and follow ramps that are a little retarded/advanced respectively re exhaust and inlet, I am just off out for dinner now but if you want me to explain a bit better later I can do, Rick

 

[solarman216]

If you really want to keep your advanced cam timing for breathing better, another way forward rather than re grinding your cam and a lot easier is to grind the inlet valve seats so the valves sit deeper into the head, this will get round piston kissing the valves but not sure how this will affect rocker arm geometry, shortening the valve stem should get round that if it is a problem, the exhaust valve will be fine as it closes earlier, it is the earlier opening of the inlet that is the problem, sinking it into the head should solve that as well as preserving the 9mm opening lift, you will however lose a little on the compression ratio, it is all a little swings and roundabouts, Rick

 

[makeitfit]

Thanks Rick, that's a new angle to think about :lol
I'm not worried about loosing a bit of cr , plenty of boost available to fill that void :sly
I'll ask the head machinist what he reckons on cutting the valve seat deeper.
We had thought about reaming the piston head a bit but frankly I can't face taking the engine out again
Exciting all this learning stuff

 

[luke1987]

Only just seen this but Rick is right the 9mm lift might be a little high especially as the head has now been skimmed. The other way around it would be to pocket the pistons slightly to accept the increased valve lift its easier to have done than grinding and tipping valves.

 

[makeitfit]

Thanks Luke but I really don't fancy dropping the engine again, I'd rather get another cam cut.
That said can you tell me if I'm going in the right direction ?
I understand that if I advance the cam timing I'll build low down torque in place of top end performance . Therefore is the cam at present in stock timing position, effectivley advanced , or, do I need to move it on the one tooth to get it advanced ?
I've gone round this so many times and I can't quite pin it in my head :nenau

 

[solarman216]

Two things Pete, one the old gasket had been compressed so against a new gasket will be thinner, second if you go from stock timing you will do an inlet valve unless you modify it, no choices here, as Luke says you can modify the piston crown, could even do it yourself in situe kitchen hinge cutter comes to mind :sly, just monitor the depth, Rick

 

[luke1987]

Pete once you set the bottom end to 109 past tdc did you set the cam to its max lift and pop the sprocket on?

 

[makeitfit]

Pete once you set the bottom end to 109 past tdc did you set the cam to its max lift and pop the sprocket on?

Yes and there's no chance of it working there as inlet valve stops the piston

 

[makeitfit]

Also as matter of observation, the inlet opening starts about 30 degrees earlier than cam data , according to the dial gauge anyway ?

 

[makeitfit]

Two things Pete, one the old gasket had been compressed so against a new gasket will be thinner, second if you go from stock timing you will do an inlet valve unless you modify it, no choices here, as Luke says you can modify the piston crown, could even do it yourself in situe kitchen hinge cutter comes to mind :sly, just monitor the depth, Rick

Good point re the gasket.
As for crown cutting , I think you could be on a roll Rick :thumbs
My local blacksmith has one of those massive electro magnet pillar drill things.
I feel a solution presenting itself