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Author Topic: Red Hot  (Read 34160 times)

lendusaquid

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Red Hot
« on: September 27, 2008, 12:17:48 AM »
Does the piston crown ever get red hot?. I ask because ive taken the engine apart to change some parts and found some crusty oil inside the piston at the top. Methinks it is there because the piston crown is getting to hot.Is this possible?.The engine does seem to get tight when it has been running a few hours on max load.Thats between 2.8-3kw.

mobile_bob

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Re: Red Hot
« Reply #1 on: September 27, 2008, 05:01:17 AM »
the piston won't get red hot by quite a stretch however it might get upwards of 1000 degree's under a heavy load
and there might be some localized heat well in excess of that, but likely under red hot in any event.

the oil will probably start to char and coke on the underside at temps over 400-500 degree' if there is not much oil being splashed up
to cool the piston,

is your engine DI or IDI
DI engines have the injector firing directly on the piston of course so that region would get hotter

but it would take alot of fuel to heat as much cast iron in one of those pistons to red heat, probably far more than can be delivered by the pump.

how much coking do you have under there?

bob g

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lendusaquid

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Re: Red Hot
« Reply #2 on: September 27, 2008, 10:34:20 AM »
Its IDI running on wvo with a tad of acetone .High pressure line heated to 120 deg C. Its a 1930's engine with a Indian piston. The crusty oil was in the centre of the crown.There was enough there for me to worry about it dropping and getting into the bearings.

oliver90owner

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Re: Red Hot
« Reply #3 on: September 27, 2008, 12:41:31 PM »
lendusaquid,

I would be checking nozzle pattern and to see if there is any carbon in the combustion chamber. Getting into your bearings is a long way off.  Getting into the ring grooves will come first, along with possible scoring of the bore.

If your fuel is viscous it needs thinning before the IP as well - it could be loading it up too much, but that will not cause this problem.

It would appear that your fuel is not burned/atomised properly and is sticking to the piston as the gases expand into the piston area.

Question:  Do you stop and start on diesel? 

You may also be close to the limit on available power from the old girl (sorry sexist comment!) especially if there is any DC output not accounted for (startomatic battery charging).  May be over-fuelling in an attempt to carry the load which will just make things worse.  Is your pop pressure correct?  Leak down on the nozzle good?  Any fouling in the nozzle valve causing poor spray pattern?

Your comment of seeming to be tight would make me check out the piston rings and grooves as well.

Regards, RAB

MacGyver

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Re: Red Hot
« Reply #4 on: September 27, 2008, 04:15:53 PM »
the piston won't get red hot by quite a stretch however it might get upwards of 1000 degree's under a heavy load
and there might be some localized heat well in excess of that, but likely under red hot in any event.


"Faint Red" = aprox 930F
"Blood Red" = aprox 1075F
"Cherry Red" = aprox 1375F

Steve

JKson (PS) 6/1 'roid & ST 7.5

mobile_bob

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Re: Red Hot
« Reply #5 on: September 27, 2008, 04:54:08 PM »
if i were you i would also take the cover off the side and check to see if your dip stick is correct
it might be a bit too long and you may be running very low on oil.

if there is not enough oil being  thrown up under the piston, what little there is will do little to cool the piston

don't take long to check, so you might wanna give it a peek and see.

i know for a fact that the indian dipsticks can be way off!

i know of a 24/2 twin petteroid that was so low in the crankcase that half the pickup screen to the pump was exposed
and the dipstick indicated it was full.

bob g
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oliver90owner

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Re: Red Hot
« Reply #6 on: September 27, 2008, 08:19:39 PM »
Mobile Bob,  lend us a pound said: Its a 1930's engine

No dipstick.  A proper Lister.  Splash oil is supplied by run back from main bearings into the splash pan.

regards, RAB

lendusaquid

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Re: Red Hot
« Reply #7 on: September 27, 2008, 11:41:37 PM »
Thats right,no dipstick. RAB,its crud inside the piston at the top,not on the top.There was some carbon on the top but that was because i forgot to switch the line heater on a couple of times.I run for 10-15 mins on Diesel then switch to veg.

Tom

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Re: Red Hot
« Reply #8 on: September 28, 2008, 05:27:42 AM »
What kind of oil are you using? And how tight is the piston in the bore?
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

mobile_bob

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Re: Red Hot
« Reply #9 on: September 28, 2008, 06:32:19 AM »
ok, maybe i am using the wrong term for you folks on the other side of the pond :)

dipstick over here means the thing you pull out to determine if the crankcase has enough oil
you know "low.... full"

i am not talking about the dipper attached to some engines on the conrod lower cap.

having never seen an original 1930 lister, how do you check the oil level?
how do you know whether there is sufficient oil in the crankcase?

believe me i am painfully aware of the wholly inadequate big end oiling scheme used by the lister engineers
with the top holes in the upper rod brg area and the grooved upper brg.

yes i know it works, but i would have fired the engineer that suggested its use to start with.
that design sorely limits the power density of the engine, likely good enough for 3/1 and 5/1, and maybe 6/1 if all is
very good,, but over that and there are issues as evidenced by lister going to various other means of getting oil up there
with dipper, hollow dippers etc.

anyway, my question still stands,
how do you know you have sufficient oil in the engine? and are you sure it is adequate?

i would sure check to make sure, for obvious reasons.

as i previously alluded to, it is the oil splash up under the piston that cools the piston, you need to make sure you
have adequate oil getting up there.

i find it hard to believe that the engine reportedly runs fine, doesn't smoke unduely, which would indicate that
there is no real serious issue with fueling causing excess heat, that if there is enough oil getting up there it could not keep the
piston cool enough not to coke up the underside of the piston top.

bob g
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oliver90owner

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Re: Red Hot
« Reply #10 on: September 28, 2008, 07:33:41 AM »
Bob,

You can keep pouring in oil until it overflows!!  No problem, only a mess.  The oil reservoir is in the bottom of the crankcase and is only drawn upon by the oil pump (to one side).

This oil is pumped to the main bearings under no pressure.  Gravity then takes over, oil into the mains and the excess (well, all of it actually) draining back toward the sump. 

On it's way oil collected in the upper tray, which then overflows into the sump.  The oil in this upper tray is always overflowing to the sump, hopefully, and is the constant level device for ensuring the dipper throws oil at a constant rate and never runs out of oil for slinging until the oil pump inlet towards the bottom of the sump is exposed. 

Absolutely a master stroke of lube.  Bottom sump alowed crud to settle relatively easily, big end was oiled until both mains and big end became short of oil(sump empty!!!.  No stress on the oil pump, flooded suction and only needed to lift to open-ended pipes. 

The slinger was used on countless engines prior to the CS - mainly spark ignition, so those were less highly stressed in the big end area.  That, I believe, led to the larger diameter crank being fitted soon after the CS was produced, not because the crank was weak but simply that the bearing area needed to be larger for the extra loads (big end babbit got pounded into sumission  on some early engines?)

Much higher-powered multi cylindered engines used an oil squirt technique for many years ( Wisconsin statioary engines in the 40s/50s, Oliver tractor engines into the 50s to name a couple of US originated engines).  Many early stationary engines had a gresed big end bearinf (International Harvester for one).

lendusaquid,

Oops, I obviously read your post wrong, or interpreted it wrongly.  Ok, crud will mostly finish in the bottom of the sump.  Perhaps need to use a better oil - fully synthetic would take the excessive heat much better than a straight dino.  OK if the engine is fully run in, ring seating wise.  Might be very unlucky and actually block the big end oil holes.

Regards, RAB

GuyFawkes

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Re: Red Hot
« Reply #11 on: September 28, 2008, 10:46:00 AM »
There is a lot of rubbish being talked about in this thread.

1/ Oil serves three purposes, it lubricates, it carries away heat, and it carries away dirt.

2/ multigrade oil like 5W40 is not a mixture of 5 weight and 40 weight, it is 100% 5 weight with some fancy chemicals added to make it act like 40 weight, as soon as these chemicals wear out, eg by age or cooking, you end up with straight 5 weight.

3/ Synthetic oils have their uses, japanese motorcycle engines etc, they also have places where they are totally inappropriate.

4/ detergent oils keep crap in suspension, non-detergent oils do not, like the synthetic vs regular issue, detergent oils are appropriate for full flow, full pressure lube, full filter engines, not listers, non detergent oils are what you use in an engine like a lister which is designed to have a deposition sump where the crap gets dropped out of the oil.

5/ bob thinks the lister CS lube system is shite, bob is wrong, my engine for example is over half a century old, what is right for a japanese motorbike ain't right for a medium speed stationary engine, splash lube systems literally cannot fail in operation, and they are appropriate to the power density of the engine.

now the biggie.

6/ there is complete crap being talked about here with piston temperatures, and I mean complete crap.

Just because the combustion process is producing gas that is approaching a thousand degrees does not mean that the piston gets anywhere even remotely near those temperatures.

Hello, there are enough examples of nutters who have in extremis or just for the hell of it made hardwood pistons and in every case the engine runs, they only time wooden pistons fail is when the pressures kill them, they never charred into dust, 1/16" alloy cap (with no way to disperse heat to the wooden piston) was enough.

Any time you doubt me it is easy enough to pop and injector (DI) or a head or an exhaust manifold (2 stroke) and probe actual piston crown temperature within 60 seconds of the bitch having been screaming at full song for ten minutes.

Pistons (as far as we are concerned) don't get very hot at all, at 210 celcius diesel burns, at 180 celcius it boils, yet you can get excess diesel pooling inside the piston crown in a running engine and poorly atomised fuel droplets on tickover being evaporated at charred into carbon instead of being burnt.

The carbon itself on a piston crown is a fuel, which burns extremely readily (just ask anyone with a coal fire) at the right temperature, again we are talking mere fractions of a thousand degrees.

There is a complete and total lack of thought here, a CS 6/1 burns a gallon of diesel every 4 hours on song, and there is 124,000 btu in a gallon of diesel, there just isn't enough energy in the fuel at that rate of use to get anything much bigger than a 0.5 cubic inch radio control model airplane engine piston seriously hot, and even those dinky motors burn a big part of a gallon in 4 hours

The combustion event has high gas temperatures AND PRESSURES (need both to transfer heat/energy, steam engine anyone) for about 90 degrees of the 720 degree combustion cycle, an eighth, the rest of the cycle it is cooling.

I'd suggest CS piston mean piston temperatures at full load are 200 celcius or less.
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compig

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Re: Red Hot
« Reply #12 on: September 28, 2008, 02:15:07 PM »
Guy Fawkes has just written some of what I was about to !!  No way could a piston in ANY engine , let alone a CS , run at red heat !! Long before that the exhaust valve would have melted and the piston seized solid !!  Red heat on the piston crown would also vapourise the oil. It' never gonna happen !!

Just a note on oil grades , Lister CS's were originally recommended to run on 10w in Winter and 20w in summer.  They simply do not run hot enough to warrant anything heavier , in fact , heavier oil will just cause excess drag and stop oil circulation working efficiently.
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lendusaquid

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Re: Red Hot
« Reply #13 on: September 28, 2008, 07:28:06 PM »
Well my oil is to thick for a start,40weight.Will change to 20.The reason iam taking it apart is to change the conrod.The old one was bent so i levered it straight,but have never been happy about it.No doubt Guy will come round and wack me over the head with a spanner for that :).Does anyone have the tolerance figures for the gap between piston and cylinder?

oliver90owner

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Re: Red Hot
« Reply #14 on: September 28, 2008, 09:57:35 PM »
fawkes, as usual, has nothing to say constructively.  Not even read the thread.  no mention of multigrade oil, no mention  in replies of piston getting red hot.  However lendusaquid has a problem with coking-oil under the piston crown.  Only one thing doing that and it is heat.  Maybe not that much but enough.  Loads of waffle about diesel, but Lenusaquid is NOT using diesel as his fuel, only for starting and shutdown.  The MAIN fuel is waste veggie oil + acetone, an entirely different ball game than just using the fuel as indicated by Lister 50 years ago viz 90% boils off by 357 celsius, flash point (min) 55 Celsius.  We all know the chip pans do not boil away oil even at 180.  They may smoke and ignite easily and explode if water is thrown over them

No one has said you need 1000 degrees to degrade oil.  There are plenty out there who have had dipstick oil heaters in their time and have found the oil chars.

Apple wood has been, or was, used for glass-blowing moulds for many a year.  They were apparently the bees knees for glass blowing in their day.  Yes, pistons do melt.  The pulling fraternity will admit that.  Usually using alloy pistons though, not cast iron.  And over fuelling, of course.  Some Perkins engines, at one time were a little prone to piston overheating.  Some oils will char around 300.  It may well be a matter of not enough in that area to keep the oil circulating, in which case there will likely be wear on the small end bush at an earlier stage than it should happen.  The centre of the piston will be the hottest part - however hot that may be.

Fuel will not burn unless it comes in contact with oxygen.  Large droplets will protect the inside long enough to cause particulates which will then only combust at high temps and slowly.  Compare anthracite with wood.

We are not looking at 'mean piston temps', just maximum in one small area.

Forks, answer the posters problem, explain the deposits, and more importantly stop being negative.

I see nothing constructive in his post at all.  Might just as well have kept quiet for all the good points (zero) he has made.

One might wonder why we (or Listers) bother(ed) to cool these engines.  200 degrees Celsius should not even make the paint smoke on a head.  We would never warp a head, blow a gasket or any other malady we actually experience with over-heated engines.

We also know that with synthetic oil one can throw away the full flow filter and run only with a bypass type filter with extra fuel economy (due to no pressure drop across the filter).  Not something I would necessarily recommend. 

All my old tractors have a bypass filter and most are full pressure systems.  Most or all started life on straight non-detergent, but they all benefit from detergent oil, due to cleaner running (once the accumulated crud has all been removed)  The advantages over gummed rings is remarkable, and modern lubricants are to be recommended wherever they can be accommodated.  Oil is cheap.  Engine failures are not.