motor getting **** HOT!

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headdownarseup
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motor getting **** HOT!

Postby headdownarseup » Fri Nov 13, 2015 8:00 pm

More of a technical question really, here goes.
I've spent the last couple of weekends putting together (more like throwing together from spare parts) a motor that i can use for (ahem) "High Speed Seagulling" :shock:


Based on a silver century block with slightly older crankcases (CP model as it had the best crank bushes with the least amount of play in them) and an LLS cylinderhead (mid compression type if that's the right terminology) and a seagull 4 con-rod with a new gudgeon pin.
A basic pre-strip down compression measurement found 50psi in the combustion side of the cylinder. HOWEVER, piston and port alignment at BDC were so far out , there was a gap of around 1 to 1.5mm between the transfer slot on the piston and the port window itself. What to do....
i carefully skimmed the crankcase down by the same 1-1.5mm measurement and now the piston lines up perfectly while at BDC.(with base gasket fitted)
By doing this it's also allowed the piston to move further up the bore and in doing so has increased the compression at BOTH ends of the cylinder. Combustion chamber compression is now 75 psi (cold) but after a short run it rises to near 85psi (hot) and crankcase pressure seems a bit higher too. Also due to the "skimming" when the exhaust port is fully open, the piston now covers this slightly by about 2mm.
Now, the real problem with this motor is that it runs too hot for my liking. Just by touching the crankcase after 2 mins running in the bin (no prop and in neutral so the motor isn't loaded up) it's "scorchio hot". There's plenty of water coming out from the "pee hole", waterjacket has had the usual treatment so it's near as damn it spotlessly clean.
I've also had to alter the base plate timing just to get it to run anything like acceptable. (wipac gold flywheel with points not the cdi type) The basic static timing was 48 degrees BTDC (standard setting using the original dimple location.) To get it to run now i have to move the timing to near 20 degrees BTDC. ( is this too much or not enough?) It's running with an Amal 416 carb at the moment with plenty of room for improvement later on if i need it.

Have i overdone it with the compression value? Does the timing need to be backed off a smidge? Am i running too lean or too rich with the fuel? ( i don't think so as the plug tip is fairly dry with greyish deposits which tells me i must be somewhere near right with the fuel side of things)

How can i get the temperature to come down in the cylinder and keep a reasonably reliable motor without having it seize up at high(ish) revs? Having spent a few hours going through some of the "books" i'm still at a bit of a loss.
How hot do these things get when they're running at over 5500rpm's for hours on end? (i havn't got a tachometer yet but i'd guess it's running close to that maybe a bit more)

I'm all ears
HELP.


Jon


ps be gentle with me, i'd normally work on 102's but this is something different for me just to "play" with. (nudge wink)

Horsley-Anarak
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Re: motor getting **** HOT!

Postby Horsley-Anarak » Fri Nov 13, 2015 8:49 pm

If water is circulating through the water ways in the cylinder, then It can't be getting "too" hot.

When they get too hot, you get steam out of the outlet hole.
If it is steaming the steam prevents the water circulation, and thats when it gets very hot, sometimes causing a partial seize.

Dont worry, next time you are cutting the grass put your hand on the lawnmower head and see how hot that is.

Crack on Jon get it on a boat an run it.

Now we need a race venue, perhaps Hayling 2016 :lol:

H A

Adrian Dale
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Re: motor getting **** HOT!

Postby Adrian Dale » Fri Nov 13, 2015 11:20 pm

The engine must be below 100'C or steam would block the flow. From your question it doesn't sound like steam is being produced so it should be fine.

But you are running at no load so the power output may be way off even though you are up on revs. That 20' BTDC seems to be way to far advanced so fuel is still burning through the exhaust ports thus extra heat in the exhaust manifold and tube.

Give Charles a call/PM, he has a lot of recent experience on motor timing as has Allen above.

AJ

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Charles uk
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Re: motor getting **** HOT!

Postby Charles uk » Fri Nov 13, 2015 11:25 pm

Doesn't he say the heat problem is in the crankcase area?
Make it idiot proof and someone will make a better idiot.

Adrian Dale
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Re: motor getting **** HOT!

Postby Adrian Dale » Fri Nov 13, 2015 11:55 pm

mmh, yes he does. He also talks about the minimum clearance in the bearings.. so crank case/crank shaft alignment. spells seized. but that doesn't appear to be the case..

AJ

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Re: motor getting **** HOT!

Postby Collector Inspector » Sat Nov 14, 2015 4:37 am

Jon

Am I correct in that you have effectively lowered the barrel by 1.5mm 0.060"?

Are running at high RPM unloaded no prop, in a barrel?

And the crankcase is hotter than normal?

Maybe go back and raise the barrel back to where it was and run as normally with and without a prop in the barrel.

Let us know if the original ignition location turns it back to normal.

You may be taking too bigger steps in one hit is all.

Changing the barrel height up or down effectively changes the transfer timing +/- over up and down. The induction timing is also changed accordingly.

If you could explain or post a pic of the "Gap" between piston and transfer port at BDC as well? At BDC the port should be nearly but not quite completely open.

It is nice to play aye.

B
Just took a leaflet out of the letterbox, saying that there's no reason I can't have good sex at 65.

Brilliant - because I live at no. 49 so it's not far to walk home afterwards!

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Re: motor getting **** HOT!

Postby Collector Inspector » Sat Nov 14, 2015 4:48 am

Collector Inspector wrote:Jon

Am I correct in that you have effectively lowered the barrel by 1.5mm 0.060"?

Are running at high RPM unloaded no prop, in a barrel?

And the crankcase is hotter than normal?

Maybe go back and raise the barrel back to where it was and run as normally with and without a prop in the barrel.

Let us know if the original ignition location turns it back to normal.

You may be taking too bigger steps in one hit is all.

Changing the barrel height up or down effectively changes the transfer timing +/- over up and down. The induction timing is also changed accordingly. Running the motor unloaded at high RP means that the actual throttle opening will be minimal......minimal air fuel to do any effective cooling of the crankcase and rotating bits.

If you could explain or post a pic of the "Gap" between piston and transfer port at BDC as well? At BDC the port should be nearly but not quite completely open.

It is nice to play aye.

B
Just took a leaflet out of the letterbox, saying that there's no reason I can't have good sex at 65.

Brilliant - because I live at no. 49 so it's not far to walk home afterwards!

headdownarseup
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Re: motor getting **** HOT!

Postby headdownarseup » Sat Nov 14, 2015 4:13 pm

Right ok, back to the start.

It's a bitsa in every sense of the word, based on a model 75 (silver century block,LLS head, CP crankcases, crankshaft from something century like,conrod from something else century based etc. etc.)
As none of these parts were originally married together, there probably is going to be discrepencies somewhere along the line.

Me being me, i thought (wrongly it seems) that having the piston at BDC to see whereabouts the piston is in relation to the ports would give me an idea of what to do in terms of "improving" a few things. The "GAP" i mentioned is the orientation of the transfer slot on the piston against the port window of the cylinder at BDC (does that make sense)
The "alignment" was out by 1-1.5mm at BDC (transfer port fully open)
So, what i did was to "skim" the flat face of the crankcase to take up the missalignment. It's only now that i realise what i've done?
Yes the crankcase pressure has risen quite a bit (it breathes really well with hardly any blowby from the carb with plenty of "suck") , but i think the problem lies with my "heath robinson" method of skimming the crankcase. Looking at it , the squareness of the cases against the cylinder base doesn't look as good as it could do.
This might be leading to the crank bushes getting loaded too much on one side hence the heat build up through the cases. I'll know more a bit later on today as i shall strip it down for some close examination.
Also, as part of the skimming attempt, the piston now travels 1-1.5mm further up the bore and increased the compression? Good in some respects but bad in others.
The port timing is now all over the place as a result of the "skimming", but it does run ok (ish) except for the hot crankcase.
Running the motor in the test bin WITHOUT a prop will allow the motor to rev quite freely (as you'd expect) and it does.
Even at 1/3 throttle (not that high revs really) after just 1 min the cases are roasting hot! The cylinder gets warm (as expected but not hot) with loads of water circulation so i'm confident it's not a waterflow issue. I'm leaning towards friction on the bushes, or missalignment with cases/cylinder base at the moment....

The ignition timing was something i was just playing with. With the standard dimple setting gives you around 40-50 degrees static timing. (fine for a stock motor this isn't stock any more) Try as i might (and one very sore/aching right shoulder later) it will not run at 40-50 degrees. The best i can get is a half hearted cough from it. Everything with the ignition is as it should be in terms of points and plug gap etc.
SO, redrill the dimple closer to 20-30 degrees (static timing) and it runs quite nicely at that.
I've not had the motor on a transom yet for any serious testing, just trying to get things basically right before it heads to the water.

If all else fails i can always start again with another set of cases as everything else with this motor is basically untouched. ( i have a few sets lying around that will do the job) and hit the "books" again.

So, quick re-cap
The cylinder head ( mid compression LLS type) is basically stock.
The cylinder is basically stock (except for a light trim-up around the transfer port at the base of the cylinder)
The crankcases i reckon might be too far gone by now as a result of the "skimming"
Crank/rod/piston are still stock.

(note to self: measure twice-cut once, slow down and think more jon) :roll:

all comments welcomed gents
Jon

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Charles uk
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Re: motor getting **** HOT!

Postby Charles uk » Sat Nov 14, 2015 5:05 pm

When you strip this power head Jon, ensure the con rod is assembled correctly, the end cap is on the right way around & the shell bearings are the right way around, any mistakes in this area can generate quite a bit of friction, but any heat generated by the bigend would normally take more than a couple of minutes to get conducted to the outside of the crankcase, this quick would imply the main bearings are struggling, bent crank or crankcase mounted against the cylinder at an angle causing the drive shaft to load up the bearings.

Too hot to touch is a lot of heat/friction when you have 400 litres of petrol soaked air passing through this chamber every minute!
Make it idiot proof and someone will make a better idiot.

headdownarseup
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Re: motor getting **** HOT!

Postby headdownarseup » Sun Nov 15, 2015 12:26 am

My thoughts exactly Chas.
Well, it's stripped down again and.....well it's very oily in the bottom case,so much so that it's what i would call excessively oiled! (too much crankcase pressure perhaps) Total running time for this motor so far has been 5 mins. to give you some idea. (pics below)
Also just by looking at the joint face of the cases to cylinder base it's definitely not square at all (as you said loading the crank on one side) and the crank shows "shiny" spots with a slight hue of blueing! (something somewhere causing either friction and/or heat build up through the bushes)

No matter, i'm starting again from scratch using a stock pair of cases from a WSPC which i reckon will be of similar age to the cylinder i'm using.
I did pay particular attention to make sure everything on the crank/rod was in it's correct place so i'm confident that nothing is amiss here.
IF, later on i find that the crank is slightly bent somewhere, i can swap out with a choice of 5 others. No worries.

So starting from the beginning again with stock cases and the same crank/rod combination i've taken a few rudimentary measurements of the cylinder to see what's what and where some things can be improved.
Starting at TDC (using a homemade timing disc and making pencil marks on the disc i've transferred these into a "language" i can understand)
EXH port opens at 100 degrees after TDC Transfer port opens at 118 degrees after TDC BDC Transfer port shuts at 70 degrees after BDC EXH port shuts at 86 degrees after BDC. ( allow + or - 2 degrees for errors at this stage with my timing disc and measurements)
Giving this cylinder an exhaust open duration of 166 degrees and a transfer port duration of 130 degrees.
Reading through the "books" again, i notice that some say that to gain some power an exhaust duration period of 178-180 degrees for a 100cc cylinder in a kart engine is ideal. (i'm just using this as an example as it seems the closest thing to a seagull cylinder for the moment) mind you the kart engine is revving to 10250 rpm's at this point, unlikely that a seagull is ever likely to see these sorts of speeds in stock (ish) form.

One of my first questions is going to be what actually controls the port opening in a seagull cylinder? Is it the piston crown or the top ring?
If it's the crown then my measurements are pretty good, if it's the ring then my measurements are off a bit. (allow + or - 2 degrees for any errors in my measurements)
Please advise.

Next, when at BDC for some reason this replacement set of cases seems to match up much better with the transfer port. (i can't see that the piston being opened a long way past the port will flow any more fuel/air through the port than if it were level with the port) so with this in mind i'm quite happy so far. (no need to skim the cases) :roll: Looking through the exhaust port when it's fully open, the piston doesn't cover as much of the port as the last set of "skimmed" cases.
Please advise.

Another thing i've noticed is by looking and comparing various pistons, the crowns/deflectors dont always seem to look straight by eye (or is it just me)
I've dug out a straight(er) looking piston if this is going to cause issues.
Please advise.

Not rushing this time!

Jon
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Charles uk
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Re: motor getting **** HOT!

Postby Charles uk » Sun Nov 15, 2015 1:11 am

That's what you'd expect, petrol/oil particulate spray enters crankcase from carb hits the high temperature parts & the petrol evaporates leaving the oil which doesn't evaporate behind lubing the crank well, but not the upper cylinder.

Port timings are symmetrical either side of top & bottom dead centre, your exhaust on your measurements is 80 bbdc & 86 abdc, so please try harder!
Make it idiot proof and someone will make a better idiot.

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Re: motor getting **** HOT!

Postby Collector Inspector » Wed Nov 18, 2015 10:48 am

"Port timings are symmetrical either side of top & bottom dead centre, your exhaust on your measurements is 80 bbdc & 86 abdc, so please try harder!"

That killed it aye Charles.

B
Just took a leaflet out of the letterbox, saying that there's no reason I can't have good sex at 65.

Brilliant - because I live at no. 49 so it's not far to walk home afterwards!

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Charles uk
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Re: motor getting **** HOT!

Postby Charles uk » Wed Nov 18, 2015 12:15 pm

One of my roles as a moderator, Bruce is to ensure that our more experienced posters, post accurate figures, so that any guests coming on here to find the exhaust timing on a WSPCL don't get wildly inaccurate figures that are impossible to recreate on their Seagull.

It's hard enough finding the right components, without encouraging newbies & guests to damage them beyond repair & get disheartened trying to emulate inaccurate specifications!
Make it idiot proof and someone will make a better idiot.

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Re: motor getting **** HOT!

Postby Collector Inspector » Wed Nov 18, 2015 12:48 pm

Maybe have a think as to "How" you moderate.

Maybe have a think as to the "Words".

Maybe have a think for the future interested punters.

Very tacky Mate.

Yes you may be correct in what you just posted but even that is very......how can I say this......indelicate.

The topic is dead and thank you still.

B
Just took a leaflet out of the letterbox, saying that there's no reason I can't have good sex at 65.

Brilliant - because I live at no. 49 so it's not far to walk home afterwards!

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Charles uk
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Re: motor getting **** HOT!

Postby Charles uk » Wed Nov 18, 2015 12:57 pm

Perhaps your right, I know Jon well, he's a pomme & pommes are not that delicate.
Make it idiot proof and someone will make a better idiot.


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