Single point seizure

[Mekanix]

Recently looked at a top end where only one part of the piston scored the cylinder.
It was in line with the top ring end gap.
Installed another to end and same symptom.

Ideas ?
Guy said it shut off while running full throttle but did start back up. Just rattles now.
Ring end gap is about 18 thou.

I'm thinking either cooling as in the lower cylinder drains aren't allowing any flow out of the cylinders creating a hot spot. It did warm up very quick and felt almost hot on each cylinder after 30 seconds of running.

 

[GGuillot]

Recently looked at a top end where only one part of the piston scored the cylinder.
It was in line with the top ring end gap.
Installed another to end and same symptom.

Ideas ?
Guy said it shut off while running full throttle but did start back up. Just rattles now.
Ring end gap is about 18 thou.

I'm thinking either cooling as in the lower cylinder drains aren't allowing any flow out of the cylinders creating a hot spot. It did warm up very quick and felt almost hot on each cylinder after 30 seconds of running.

It's quite possible that fitting in the hull exhaust piece is clogged, it would directly be responsible for no flow coming off the bottom of the cylinders. During my resto I discovered this fitting completely clogged, but I only found it because I removed this piece when doing the reapplying of gelcoat on the hull bottom.

It's definitely masked and difficult to detect because water is always blowing out the exhaust coming from upstream. It's a pain to reach back there and remove the fitting, but I'd check it out.

 

[Mekanix]

I'm just wondering if that alone can cause an overheat that leads to scoring in just one location on the cylinder. It feels like there is not enough heat being removed so I'm looking at that as a possibility but also looking at a possible lean condition ?

 

[GGuillot]

I'm just wondering if that alone can cause an overheat that leads to scoring in just one location on the cylinder. It feels like there is not enough heat being removed so I'm looking at that as a possibility but also looking at a possible lean condition ?

That line off the bottom of the cylinders is 5/16" going back. Curious if your pee indicator (1/4" line going back) is flowing strong at idle or a slight dribble. I'd think a higher flow at idle would indicate a higher back
pressure in the system.

 

[Mekanix]

Flowed pretty much normal. I did notice that the drain line had a check valve in it. I'm going to have a look at it no matter what. Just still confused if that alone can cause this sort of seizure or if it's a combination of things.

 

[GGuillot]

Flowed pretty much normal. I did notice that the drain line had a check valve in it. I'm going to have a look at it no matter what. Just still confused if that alone can cause this sort of seizure or if it's a combination of things.

I never noticed a check valve in the drain line or anywhere when routing lines and fittings. Where are you referring to? I'd think it's possible to get enough flow on the top of the head to keep the over temp from coming on, but if there's no flow off the bottom of the cylinders you could get a hotter than normal temp to cause issues.

 

[mikidymac]

For the most part those a just drains. Keep in mind the cylinder water flows through the exhaust manifold.

If it’s just seizing at the ring gap I would suspect an out of round cylinder or the ring gap being too small and expanding under heat.

 

[Mekanix]

This is on a 97 challenger. The engine is below the water line so they added a check valve on that line.

Both the old top end and new top end had the exact same failure on the mag cylinder and only on the upper ring ends. It does look like too little ring end gap even though it had 18 thou clarence which was the max spec for new. I cant tell if it's an overheat from being lean or if its undercooling issue. Or even an oiling issue. The oil pump is still on and it was premix for break-in.

I've been readin group K about seizure types and more often they found that it is the oil film being removed that causes this kind of issue. Or visual signs of metal to metal contact.

 

[Mekanix]

Tore down the top end and carbs again.
Co formed the oil pump was worki g and that the fuel lines and selector are air tight up to the carbs.
Rebuilt the carbs. Had good pop off. Fuel pump check valves were allowing some leakage and new valves fixed that.

Attached some pics
Does this look too rich or too lean ?
Pto side on the left has just the right burn and wash pattern. Mag side as you see it. Very clean. So I'm thinking too rich and it washed away the oil film? Or too lean and it burned off the oil film.
Found a little fuel in behind the fuel pump diaphragm.

 

[GGuillot]

My thoughts on this, mechanically, what are the chances of the same exact cylinder having the same problem with a new top end? The pto and mag were both assembled the same correct? In that new top end pic it looks like the mag cylinder is not even getting fuel/oil at all, it's way too clean. It would be like a dry cylinder running, which would cause the metal to metal wear.

Quite possible a bad oil injection going to that cylinder, maybe you could take the oil pump off and do a bench test with a drill and see. But it's awful clean, and you said it's premixed for break in..

You went through the carbs, but it seems something delivering fuel/oil is not working effectively causing the issue on the mag cylinder. Along with oil injection, that would be my focus, the carbs, going through them....again.

I don't think the issue is cylinder assembly/ring gap/wall clearance, not twice in a row on the same mag cylinder.

 

[mikidymac]

The piston on the right is super rich and washing away everything including the oil. IF it is premixed and injected then it's not an oil problem.

As you can see below the richer it is the cleaner the piston will be and the leaner it is the more black and sooty it will be because it is so hot.


Yours appears to be dumping in a ton of fuel.

 

[Mekanix]

Now I found something!
Pinhole in the fuel pump diaphragm.
There was fuel behind the diaphragm but only 1/4 of the way up.

With the carbs off and the oil pump wide open, cranking the engine proved that there was definitely oil flow. Each nipple was flowing what I would expect at 500 rpm.
There was always smoke and the typical oil smell from the exhaust as well.

I did notice that the mag cylinder spark plug was 10 degrees colder than the pto at idle.
(Using a laser thermometer)
Found the plug was a little fouled because that changed when swapping plugs.

 

[Mekanix]

Runs better now. Can be confident that both cylinders are burning equally but now I've found that it has that midrange miss and it's only when the main jet fully kicks in that it smooths out so around 6000+

For testing I tried finding the worst spot. It was around 1/4 throttle or maybe a little more. That put it around 4600 rpm. Choke made it fade out quickly turning off the fuel selector a little at a time smoothed it out perfectly. (Was just a short test to lean it out to see results.)
So either pilot jet is too big or the main jet is contributing too soon or maybe even pop off is too low....

Also hard to start. But give it choke orchard throttle and it starts to come to life.
Compression is 170. (Fresh top end, .75mm over)

Removed the return line and tried cranking while cold in the water to see how much flow there was. There was a good stream and the engine took it's time to kick. Probably 10 seconds before it had a stable idle. That was with no choke or throttle. I was thinking that maybe the fuel pump wasn't flowing enough and that's why it was so hard starting. Looks like that is not the case.

Also a bogg of idling for 10 seconds which then recovers when past 1/4 throttle.

 

[GGuillot]

What would bring the compression up that high? is it the overbore? thinner base gasket?

170 seems a little high with a stock head..

 

[Mekanix]

0.75mm overbore shouldn't be that drastic. Stock head. 6 Hole base gasket with a squish of 1.8mm. And a trust worthy gauge I check for cal at work.

I'm not sure why it's so high. I'll have to cc the dome to be sure.
I'm at sea level here as well.
It is a wsm kit as well maybe they changed the dome peofile.

Almost all of my 787 builds end up like this with close to 170 psi.

 

[mikidymac]

If all of your builds are that high then either your squish or your gauge is reading high. Every one I have done is at the stock 150 psi.

 

[GGuillot]

0.75mm overbore shouldn't be that drastic. Stock head. 6 Hole base gasket with a squish of 1.8mm. And a trust worthy gauge I check for cal at work.

I'm not sure why it's so high. I'll have to cc the dome to be sure.
I'm at sea level here as well.
It is a wsm kit as well maybe they changed the dome peofile.

Almost all of my 787 builds end up like this with close to 170 psi.

You may be on to something with the sea level factor, I used to live in South Louisiana and a lot of compression tests on vehicles would always read slightly higher and at drag strips it ran slightly faster. @etemplet lives in South Louisiana and he said he's getting 170 on a 787 rebuild also. South Louisiana sits anywhere from below sea level (New Orleans) to about 50 ft. above (Baton Rouge).

I used the same WSM gasket kit on my 787 rebuild, 6 hole gasket, but I got 150 per cylinder, I'm 220 miles North of the Gulf Coast in Alabama and I think we sit about 250 ft above sea level.

 

[Mekanix]

It fluctuates from -300 to +1000 where I am. Depending o the time of year. Right now it's mostly 0-200 each day I've tested it.

 

[mikidymac]

I am at 300' above sea level and it's always 150 psi. Not saying it's not possible but highly unlikely.

 

[Mekanix]

Yeah I've always thought it was weird. But when i test my gauge and bring up the pressure slowly I can get it to match within what I can read between the lines. But I wonder how the bumps from compression strokes affect it.
I'm going to get another gauge just to test or maybe make a T adapter to have two gauges on one line lets go nuts lol

 

[mikidymac]

More importantly is consistent even pressure so I wouldn't worry too much about it.

 

[etemplet]

Dang strange. Scouring in the same location seems mechanical. Looks like you replaced the piston so that would partially eliminate a piston related issue . I wonder if the piston ring is clipping the port (not everyone champfers the ports properly when the cylinder is re-bored) or something is out or round as Miki says... I agree compression readings are consistent and equal is the key to happiness as long as they are 150ish of course.

WSM pistons expand a little faster than OEM as mentioned in the clearance recommendations in the Top End paperwork. (.0045" to .005") The rings are generally at the top of spec for WSM rings but Maxx is about .045" so I don't worry too much about it. Good Luck !!

 

[Mekanix]

Mechanical maybe but I'm not sure how. I replaced the pistons, bearings, cylinders, all gaskets, eaves, and I chambered the ports. Funny thing is where it wore the most was in line with the top ring gap.
Oh and they were bored to that spec as well as in 4.5-5 thou. I checked before I installed it.

This kit was originally a complete top end swap I was setting up for myself and this guy needed it more than me. I just cant see what I could have missed.


One more thing that just came to mind is that the oil pump top screws came loose the first time it melted down.
I only noticed because the cable was so frayed that the pump was stuck full on and the bracket moved when i tightened the cable. so after tightening the cover and making sure the pump was set I held it wide open while cranking to make sure there was oil flow. There was plenty. Even after this happened the second time I checked and had good oil flow and premixed a little.



Have you guys ever cleaned a carb so well that it opened up the portstoo much created an over rich condition in the 1/2 throttle range ?

 

[etemplet]

Well, you surely covered all that then....

 

[etemplet]

How about RAVE Valve Clearance ?? Were the valves fitted to the new bore??