Technical valve to piston clearance

[fostertom]

Here's a question from Bodge City - laugh but help me if you can!

Putting a 1368 block under a standard unaltered Punto mk1 ELX85 (1242) head complete with manifolds, ECU etc all from the ELX85.

I checked on here as best poss, whether it would work, hoping for a simple bolt-together job. We discovered and solved some things along the way but now we got problems with valve to piston clearance.

Question is, when mix'n'matching blocks/pistons with different heads/valves/cams, how exactly to check for valve to piston clearance - or fouling as we have?

Using plasticine, turning over carefully by hand to the point where it locks, to see where it's got squeezed to nothing after taking the head off again.

Trouble is, it's really inconsistent. One time a given valve seems to have clearance, next time less than none.

Seeing the engine did a couple of short runs, seemed incredibly lively (high CR), before suddenly bending all the inlet valves, we don't know why we have clearance (albeit prob minimal) one time, then less than none on the next check.

Is it the hydraulic lifters? We squeeze them down to nothing but still get fouling, no chance they've got pumped up again. Another time they're running, so pumped up, and we have clearance.

Any ideas? We are desperate - so near to a result but something ....

 

[motoguzznix]

Tom

Best would be to install a set of 4V pistons. Since the camshaft of the 1,4 16V may be different to yours, checking of valve clearence is also necessary with the new pistons.

To check the clearences, I would install at least on one cylinder a set of rigid lifters. Either manufacture them by welding or screwing together some stock lifters or use a lathe to produce a set of 4. They should allow almost zero valve play.

Using the 2V pistons undernath a 4V head maybe a disaster - CR, combustion chamber shape and clearences are difficult to get in working order. To get valve clearence, you may have to cut a hole in the piston crown...

Good luck
Ernst

 

[fostertom]

Thanks but this all 16v kit. The head, cam etc is still the same 16v (1242) 85ELX as ever - only the block has changed, from 1242 16v to 1368 16v.

Why doesn't a hydraulic lifter that's been squeezed down to minimum, act like a solid lifter, for clearance checking purpose? The engine is being turned half a rev by hand - no chance of any oil pressure pumping the lifters back up.

But what I don't get is, no adjustment on the lifter/valve. How does anyone adjust to zero with a valve that may be a bit longer, or more deeply sunk into the seat?

 

[Ralf S.]

The 1368 has a bore and stroke of 72x84. The 1242 is 70.8x78.9... so first off, you're going to have problems with the physical dimensions of the combustion chamber.

The 1.2 head will overhang the 1.4 bore (i.e. the 1.4 piston edges will potentially foul on the lip of the 1.2 head, which is projecting over the cylinder.

Second problem is that the valves on the 1.2 head are closer to the centre of the cylinder than they would be on the 1.4... since the 1.4 has a dinner plate sized cylinder bore and the 1.2 is a tea-cup... albeit the difference is just 0.6mm on each edge. This may or may not matter depending on the piston crown shapes but if the pistons have cut-outs then the 1.2 valve might be fouling on the 1.4 piston/cut-out. Also the valve angle on the 1.2 head may be steeper than the 1.4 piston is expecting...

The camshaft controls how far open the valve gets... in theory a 1.4 camshaft should give higher lift (longer stroke allows a longer valve timing interval) but that may not be the case. You need to measure valve lift and make sure it's not going to cause a terminal problem.

More random problems.. if the crank bearings, or gudgeon pins are worn out, then the crankshaft could be moving about and affecting height of the pistons on different cycles. I'm presuming your crank is not soooo shot.

First thing is to get the head onto the block and to the point where you know it's not clouting the pistons. You can leave the valves in there but remove the camshaft so that all the valves are closed. If it hits (measure with Plastigauge etc.) then there's no point in worrying about the valves etc.

You may need to machine the head to produce a combustion chamber that lines up with the cylinder bore... then you have too worry about combustion chamber shape and detonation problems. Why are you fitting a 1242 head when the obvious solution is a 1368 head?


Ralf S.

 

[Duncan]

I have a 1242 head on a 1368 block and although I've haven't fired the engine up yet I have turned it by hand a lot and it's fine. Ming has the same setup and his works fine too.

 

[fostertom]

Thanks again.
Ralf, I'll clear up a couple of points so focus can be on what may really be happening.

"the 1.4 piston edges will potentially foul on the lip of the 1.2 head, which is projecting over the cylinder" -
16v 1.2 and 1.4 pistons don't even quite come to top of bore, so no danger of them hitting any part of 16v 1.2 or 1.4 heads, or gasket.
In fact three 16v heads - 1.2, 1.4 FIRE (mk.1 Stilo) and 1.4 StarJet (PuntoGrande), are near-identical, as far as equally-spaced chambers and valves and all same valve size.
But the bores are irregularly spaced, in 2 different patterns, 1.2 vs 1.4, as well as the differing bore diameters.
So all head/block combinations slightly mismatch - no problem apparently.

"if the pistons have cut-outs then the 1.2 valve might be fouling on the 1.4 piston/cut-out" -
The 1.2 vs 1.4 pistons do have slightly different cut-out layouts to suit their different mismatch to the heads, which are near-identical. So 16v 1.2 head/valves do fit the 1.4 block/piston cutouts, in terms of cut-out layout - but not necessarily in terms of axial clearance (that's the problem here)

"the valve angle on the 1.2 head may be steeper than the 1.4 piston is expecting..." -
Don't think so.

"a 1.4 camshaft should give higher lift" -
Not using 1.4 camshaft - using a complete 1.2 head on a 1.4 block/pistons.
But the 1.2 camshaft might have higher lift than the 1.4 block/pistons is expecting - but the thing is, it ran perfectly (1.2 head on 1.4 PuntoGrande block) until suddenly bending all the inlet valves.

"Why are you fitting a 1242 head when the obvious solution is a 1368 head?" -
Because the idea is to leave everything completely standard, as far as the 1.2 ECU sees it, with sole exception of increased cylinder capacity. On our succesful short test runs (until all the inlet valves suddenly bent) the standard 1.2 ECU seemed to handle the capacity change magnificently.
Also the 16v1.2 head/manifold etc has the great advantage of cable throttle control rather than fly-by-wire.

 

[fostertom]

So question is, why did this combination (16v 1.2 ELX85 Punto mk.1 head on 1.4 PuntoGrande block) run perfectly, very lively, for 2 short runs, then suddenly bent all the inlet valves.

But then after head rebuild, we can't even turn the engine over because valves foul the pistons axially.

Now I'm thinking we've rebuilt it with over-long valves - could that explain the fouling since the rebuild?
Not sure how it works, with hydraulic lifters - shouldn't they simply compress to automatically adjust to longer valves? e.g. valves that are more deeply sunk after seat recutting/valve grinding?

But then, before, why did all the inlet valves suddenly bend, after running perfectly?

 

[Ralf S.]

If the valves all suddenly got bent when otherwise it was running fine, then the setup should be okay.

You don't have anything variable in the valve timing.. so if the beast turns over without touching when turned by hand, then (ignoring that tolerances will reduce fractionally at higher rpm/under load) it should remain not touching.

I presume you didn't have a belt slip/tensioner problem/belt teeth going AWOL.

The valves worry me. You should the correct spec' valves required for the head. The hydraulic lifters can compensate for wear but if the valve stems are too long then the lifter will leave the valve head not seated fully and it will obviously then project into the cylinder.

The other thing that might be causing a lock is the valve springs. If you've broken one or if you rebuilt using too-weak springs, the valve(s) can float at high rpm.. that causes the lifter to think it needs to fill with oil (taking up the slack between itself and the valve stem whilst the lifter valve is open) which then "extends" the effective valve stem length - and then you get the same "interference" problem as fitting over-long valve stems.


Ralf S.