[Mk2] [Turbo] Stroker build problems: head off,found movement in pistons, excessive? help need

[RyanRs]

I have been having endless problems with the car over-fuelling so bad on cold starts that the plugs turn instantly black and the car will barely run until it gets some heat in it and the plugs are cleaned off. Maps and AFRs have been checked time and time again with no sign of fault and fuel pressure etc is good. The longer i leave the car sit without starting, the worse it is!

I have also been losing about 1/8 of a litre of oil every time i go out for a whole day having fun in it ,giving it some good WOT pulls etc, however there is no blue smoke from the exhaust when the engine is warm. -there is some when its ticking over cold after a few days no start. Valve seal symptoms.

I have been putting my thoughts toward having bad valve stem seals or even stem guides, this therefore allowing oil to drain down and foul the plugs, preventing them from firing. This combined with 1200cc injectors flooding the bores with fuel could explain why i am getting the all cold start problems and a lot of overfuelling soot on the plugs when it does decide to fire??

However. Today i took off the head. i cannot see any major sign of oil running down the valve stems, perhaps a light coating on the intake side? For my theory of oil fouling the plugs and preventing them from firing to work, the oil would have needed to come from the exhaust valves due to the angle the engine sits at, but these valve stems are dry.
Inspection of the pistons / bores shows no sign of any damage and carbon build up is minimal. However, i did notice quite a bit of movement in all 4 of the pistons and im not sure if its excessive?

Here is a clip, sorry its not the best of recordings it was hard doing it on my own. I did not have a tool to measure the amount of movement but i would say it must be about 1mm of play in all horizontal directions.



The block is a 3s with 5s crank, eagle rods & 86.5mm omega forged stroker pistons w/ceramic skirts. The engine has done about 3,500 miles and run 420 fly-bhp.

Can anyone advise?
thanks.

[Lewis Jay]

Have you popped the pistons out and checked the rings and bores lower down?

[RyanRs]

No not done that, tbh i only took the head off expecting to see leaking valve seats, i would rather not take the sump off. I am 90% sure tho that the rings are fine and the bore is the same below the piston as it is at the top as all the bores are in good condition throughout the entire length of whats visible.

Also forgot to add that compression test showed 160 across all cold and 180 +- 2 psi when hot.

[3S Service Centre]

Ryan.
A few questions spring to mind

What were the rings gaps?
Were the rings installed correct side up?
What clearance were the pistons given to cylinder wall?

If the above was good your trouble will be the cylinder wall surface, it could have been bad before assembly. I have experienced bad honing (blunt tools) which is near impossible to identify if you don't know what to look for.

James

[RyanRs]

Tbh buddy, i dont know the answer to any of those questions as i didn't assemble the bottom end. However, the guy who did buid it is very experienced and well known in the mr2 land to make very good engines. It makes me wonder if its the machinist that they use whos made a mistake in the cutting the bore size?

The hone did look good when it was new, very fine and precise cross-hatch as it should be. This is the only close up i have of the hone, not a brill pic, but you can just about see it looks fine.


All the little bits in there are just dust thats stuck to the coat of lube on the walls.
The hone marks are very faint now, very smooth surface just as they should be if the rings have worn in correctly.

[3S Service Centre]

dont wanna upset anyone so wont elaborate, but from what your telling me, and looking at that picture its the cylinder wall.

[Dale_V]

The honing there would never give the rings a chance to bed in properly, looks way too smooth

[3S Service Centre]

The honing there would never give the rings a chance to bed in properly, looks way too smooth

Correct.

[3S Service Centre]

"The hone marks are very faint now, very smooth surface just as they should be if the rings have worn in correctly."

you have been ill informed.

I have opened engines that have done over 100,000 miles stripped and have perfect honing marks, if its smooth the oil will pass the rings.

Smooth cylinders can be created by bore wash/excessive fuel too!

James

[Dale_V]

I have opened engines that have done over 100,000 miles stripped and have perfect honing marks, if its smooth the oil will pass the rings.

Correct

I have also, infact engines with more miles on and the honing has been "rougher" than what yours appear with zero miles!

[RyanRs]

Hmm, well i think ill have to get someone round to inspect the hone ,its a hard one to describe properly as theres no way of measuring these things. Would we agree tho that the horizontal rocking is excessive tho? It was defiantly not done through bore wash as i built the engine with the 540's and stock ecu in place so fuelling was as it should be.

[Lewis Jay]

Ryan.
A few questions spring to mind

What were the rings gaps?
Were the rings installed correct side up?
What clearance were the pistons given to cylinder wall?

If the above was good your trouble will be the cylinder wall surface, it could have been bad before assembly. I have experienced bad honing (blunt tools) which is near impossible to identify if you don't know what to look for.

James

These are the reasons i asked about popping the pistons out.

Bores look very smooth as already stated......

and yes theres to much movement in there also.

[3S Service Centre]

The piston movement only looks about 3.5 to 4 thou which depending on the pistons and the application could be about right. Though I am surprised a good engine builder would see that cylinder wall and think its ok.

[bobhatton]

There is only one thing you can do here and that is take the pistons out and measure the bore size against the piston size. The piston ring gap also needs checking.

A smooth finish is not good for bedding in the rings and that bad seal will allow oil to be sucked up from below when the throttle is closed such as a idle.


Bob

[RyanRs]

Well tbh that pic is not a great example of the cylinder wall as the camera did not pick up the detail very well, also the flash reflected off the surface and the coating of lube makes it look smoother.

I bot this pic of the internet, but i would say its pretty much the same quality of honing as what was done in mine..



You can still see light hone markings on it now but generally the bore feels smooth.

If there is infact too much play in the pistons than can i assume that its a machining fault and not something that i could have done through driving the car? The run in process was done exactly to the engine builders recommendations, the correct oils have always been used and the engine has been mapped correctly.

[3S Service Centre]

The machine shop can make a mistake, but the builder should be checking the tolerances during assembly and should stop when there is a problem.
If the bore was too big you get 2 stabs at finding the problem.

A) when measuring the bore and piston skirt.
B) when measuring your rings gaps

If as you say the map was good, and you have got smooth cylinder walls, its a assembly problem or bad hone.

[RyanRs]

Hmm so i assume the hone is never supposed to completely disappear then?! i always thought that the hone was to give a rough edge for the rings to grind against causing them to have a perfect seal, but now im thinking that the hone provides a path for the oil to return through as its in downward motion?

[greeny]

Its hard to say without seeing it in person, but your compression numbers seem to be up there.

Looking at the pictures on here is guessing at best.

[RyanRs]

Finally got some pics of my hone as it is now....

I think it looks ok?

[planted1]

If there are no visible signs of oil being burnt,then it must be an oil leak.
Are there any signs of oil on the floor?
or any signs that oil has been leaking after a drive.

On the other question ,
is your ignition spark strong and steady,
sounds like you could have a faulty coil imo.

cheers