ESE's works engine tuner

[F5 Dave]

In my meagre experience I'd anecdotally say that whenever I leakdown test engines, if there is a leak, the leak is inlet manifold. Probably old engines, hard rubber.

[seattle smitty]

That holed piston "looks" to have some erosion on the exhaust port side which in my limited experience is usually heat related detonation. That heat also could cause(?) the hot plug as per Wobbly which could cause preignition. That preignition could cause a shock that displaces the boundary layer locally exposing the piston crown to exceedingly hot gases and successive shocks, eventually blasting the hole we see. It would be interesting to see if the squish band outer edge on the exhaust port side has a slight roughness.

It looks to me like any piece of aluminum plate would look if you pointed your oxy/acetylene torch at the middle of it until it got shiny, then grainy, then dropped away. Shiny-to-grainy-to-hole happens in very short order (which is why gas-welding aluminum is a balancing act, trying not to let it get beyond shiny). Okay, if you look close there are some little cracks; when the aluminum was getting real weak it was in a running engine making power strokes, after all. Yes, there is some erosion around the edge of the piston crown. But that hole melted. No sharp edges, not a blasted, broken-edged hole that looks like somebody slammed the piston crown with the back of a ball-peen hammer. This piston just got HOT in the middle. Interesting that what we can see of the skirt looks fine, however.

Are those two-ring pistons? Hard to be sure, with my eyes.

[GerbilGronk]

In my meagre experience I'd anecdotally say that whenever I leakdown test engines, if there is a leak, the leak is inlet manifold. Probably old engines, hard rubber.

My KDX engine had porous castings which would allow gearbox oil to get sucked into the crankcase. It would then smoke etc. Fixed it by getting the crankcases HPC coated. Seemed to work sweet.
http://youtu.be/N1C4eJ4npn0

[wobbly]

Yea well pistons that "just get hot " just expand - and then seize in the bore.
When there is detonation - in this case caused by an overheated spark plug, dead centre in the bore, you get chemical disassociation and this causes
free radicals to be formed from preignition.
Normally this is only seen in the squish band, where the trapped end gases are subject to excessive heat and pressure.
This causes the destruction of the alloy surfaces, be they the piston but just as commonly the bore edge or the corner of the head if any.
When we have localised detonation in the bore centre it can only be caused by an overheated spark plug component initiating preignition and thus
the precursor to free radical formation.
This thought process first occurred to that clever bastard Thiel, when the Aprilia reached a certain level of power output ( never seen before I might add )
there were continuous problems with blowing holes thru pistons.
Dropping compression, running rich etc all band aided the real issue ie killed the power - until Jan discovered the real issue.
The plug was being overheated.
So the simple solution as it turned out was getting water real close to the plug threads to cool the tortured plug body - issue solved.

[Flettner]

Yea well pistons that "just get hot " just expand - and then seize in the bore.
When there is detonation - in this case caused by an overheated spark plug, dead centre in the bore, you get chemical disassociation and this causes
free radicals to be formed from preignition.
Normally this is only seen in the squish band, where the trapped end gases are subject to excessive heat and pressure.
This causes the destruction of the alloy surfaces, be they the piston but just as commonly the bore edge or the corner of the head if any.
When we have localised detonation in the bore centre it can only be caused by an overheated spark plug component initiating preignition and thus
the precursor to free radical formation.
This thought process first occurred to that clever bastard Thiel, when the Aprilia reached a certain level of power output ( never seen before I might add )
there were continuous problems with blowing holes thru pistons.
Dropping compression, running rich etc all band aided the real issue ie killed the power - until Jan discovered the real issue.
The plug was being overheated.
So the simple solution as it turned out was getting water real close to the plug threads to cool the tortured plug body - issue solved.

You know, perhaps you are right, I see the water pump impellor has been slipping on it's shaft. Too lazy to fit a small key but now I will. Also the pump is a little on the small side. The water to plug, alloy thickness in the head would be similar to your inserts we machine up for you. Also found another little problem but I'm too ashamed to tell.

[F5 Dave]

My KDX engine had porous castings which would allow gearbox oil to get sucked into the crankcase. It would then smoke etc. Fixed it by getting the crankcases HPC coated. Seemed to work sweet.
http://youtu.be/N1C4eJ4npn0

RS125 cases reputedly go porous after a while. But hpc coating. Not a bad idea to save a case.

[Flettner]

It looks to me like any piece of aluminum plate would look if you pointed your oxy/acetylene torch at the middle of it until it got shiny, then grainy, then dropped away. Shiny-to-grainy-to-hole happens in very short order (which is why gas-welding aluminum is a balancing act, trying not to let it get beyond shiny). Okay, if you look close there are some little cracks; when the aluminum was getting real weak it was in a running engine making power strokes, after all. Yes, there is some erosion around the edge of the piston crown. But that hole melted. No sharp edges, not a blasted, broken-edged hole that looks like somebody slammed the piston crown with the back of a ball-peen hammer. This piston just got HOT in the middle. Interesting that what we can see of the skirt looks fine, however.

Are those two-ring pistons? Hard to be sure, with my eyes.

The roughness you can see on the edge of the piston are just bits of burnt piston leaving the scene of the crime. Combustion chamber / squish area is clean
Yes two ring pistons.

[Flettner]

I have a 1941 Lincoln Continental V12 coupe. An engine with all of the faults of the Ford flathead X 1.5, sad piece of junk that most Connie owners replaced by the early Fifties with Cadillac V8s, as mine has. In the interest of having an actual V12 in the car, I'll eventually replace the Cad with a Jaguar sedan V12 if I live so long.

I know of the Lincon heads, we had to machine a few for Garth Hogan a year or so ago, Hogan race heads. You know, alloy with small fins and Hogan cast into them. Race, yer right.

[speedpro]

The latest seizure I had was diagnosed by the kart mechanic as being caused by an air leak. I cleaned up the piston(again) and the bore, reassembled and pressure tested and it was all good. Went to the track and seized it again. I pressure tested prior to disassembly and it was not leaking. The piston was definitely smeared up the bore but no other obvious heat indicators. Sooo . . . taking what the kart guy said and looking at it a bit differently I thought - what if it isn't a leak but just lean at revs with the throttle closed? Long story short I've fitted a larger pilot jet and the problem has gone away. Looking back over the years I've had similar seizures and wonder how many could have been avoided.
I still have problems believing that being a bit lean on a closed throttle could cause it to seize like it did. I've ended up with a #45 jet in place of the #40 so not a huge increase.

[41juergen]

Hi guys its me again.
After all your feedback I went further into the sims but was not successful. But than I had a look into the RZ350 and TZ250 examples from Neels. So finaly it looks like that I found the issue. I had measured the duct / passage lenght of the C port with approx. 30mm. But I didn't added the part of the charge colum which belongs to the area of the reed block / intake part. So adding some 20 - 30 mm (60mm is the lenght of the duct until the tip of the reed block) everything became fine. So may be the feeling of a mismatch for the phasing was not too wrong. Now the simu allows the ignition curve Wob posted for his RZ400, a reasonable comp is possible, etc.
Now the question is: is 60mm ok or shall I try to go down to the point were "unexpected" detos will start?
And an other question about the CC comp: I think Wob you mentioned something like 1,35 is ok for a RZ setup. Is that with transfer ducts volume included?
Thank's again for all your feedback :-) from snowing Germany

[Frits Overmars]

Are those two-ring pistons? Hard to be sure, with my eyes.

You must be closely related to Stevie Wonder and Ray Charles, Smitty. Clicking three times on Flettners picture in post #16428 will get you this:

(Click twice on this picture).

[Frits Overmars]

When we have localised detonation in the bore centre it can only be caused by an overheated spark plug component...This thought process first occurred to that clever bastard Thiel, when the Aprilia reached a certain level of power output (never seen before I might add).... The simple solution was getting water real close to the plug threads.

That, and getting the water to move. Ever wondered why the coolant pump on the Aprilia RSA125 engine looks like it has been fitted as an afterthought? Well, that's because it was. The original engine (below left) was designed with an electric pump. Then it turned out that no electric pump could even come close to the desired flow. So a mechanical pump was designed, using the impeller from the Aprilia RSW250 twin. "That should do it".
It did; it circulates 60 liters per minute for an engine that produces about 60 hp at the crankshaft: there's your rule of thumb.

[Frits Overmars]

I see the water pump impellor has been slipping on it's shaft. Too lazy to fit a small key but now I will. Also the pump is a little on the small side.

In view of the above rule of thumb, most pumps are, Neil.

[Dutch Fisher]

The solid pin will be heavier and obviously this affects the balance ie it will make the factor lower.
Hollow pins do have one issue though and that is if the press fit is designed correctly for a solid pin then the fit will then be insufficient.
Hollow pins need more interference, as they crush - loosing some of their OD as they enter the hole..
The fit must be correct for the hollow pin for another reason - as the do crush, then if the press is too heavy the pin will "barrel " down
at the ends where they enter the wheel, and this is bad for the rollers as then the pin isnt parallel.
What size do you need.

Recommended interference fit for hollow/solid ?
Pressure reading your likely to see on press gauge ?

[F5 Dave]

Frits would be horrified to know what Mike and I are currently using for water pumps on our MBs.