Unforgiven Project

at least some of the damage appears to be the result of inadequate ring end gaps
Id be looking a a minimum of .007-,008 per inch of bore diam., on ring end gaps
I don,t think ID gap the next set any tighter than about 30-32 thousands,
and if it was my engine build,
Id certainly consider going for a 32 thousand minimum ring end gap.
once the heat expands the rings enough for the rings endgap to touch ,
even for a fraction of a second,
the ring locks to the bore wall and the piston ring groove wall is broken

http://garage.grumpysperformance.co...ing-piston-to-bore-ring-seal.3897/#post-10316

http://garage.grumpysperformance.co...ng-and-basic-piston-ring-info-youll-need.509/
004-how-to-install-piston-rings-diamond.jpg

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Notice that all the melting took place opposite of the spark plug.
The burn marks on the pistons will rub off with a little
elbow work..
The melting occurred in the 0.040 quench area.
Plugs are NGK 9's

Now I remember that when the dial indicator was on the pistons
when I was measuring zero deck...... I could rock the piston and it would move
out of the bore 0.003 (on the rocked side)

The pistons measured 0.002 below deck height

#1 , #2 ,#3 , #4 , and #8 piston where the only damaged pistons...

I am not sure how to read what caused these pistons to melt
and not effect the others..

Anyway... I spayed the cylinders with WD-40 then doused the very well with
Marvel Mystery Oil and set the heads back on
until I am ready to rebuild.

For now... it looks like I can run a hand hone to gain
cross hatch ( I would like to open up at least 0.0015 for extra
piston to wall clearance)

New pistons and rings and some new bearings
since i'm in there and I will be good to go.
 
Grumpy.. you replied while I was finishing the post.:p

So that is what rings touching looks like?
They put pressure on the land?

I was going to ask about the gaps with the next ones.
These were gapped at 0.26 on both top and bottom rings.

I do appreciate the advise on the 0.030-0.032 gap.
Now... knowing what the engine produces, I can't help
but think the wider gap will not have any negative effects
on compression. If anything... it would benefit all the way around.
I would have to go back and look at the boost charts....
but using 11.5:1 static and 10 psi boost I think the effective
compression was somewhere around 18:1
 
26 thousandths on a supercharged engines just a bit tighter than the heat levels will pemit
yeah Id sure stick with a minimum of 32 thousandths end gap on the rings and 34 thousandths would not be out of the question.
 
Thank you Grumpy... I really think I dodged a bullet on this one.
At least the pistons stayed together and on the rod!
 
PLEASE USE AN OPEN MIND WHEN READING THIS THOUGHT.....

That broken rotor issue I had with the replacement motor has been gnawing at my brain since I discovered it.

Going back to when I pulled the race motor after it blew up....
I had pulled the distributor before I removed the engine from the truck
so as not to take a chance of the engine tilting back and breaking the cap
against the firewall while lifting the engine out of it's bay.

I had removed the wires from the spark plugs and left them connected to the cap.
I set the cap on the bench, and then removed the distributor
and set it on the bench as well.

After removing the engine, and mounting it on the stand....
I wanted to put the distributor back in so it did not get miss placed.
I did this because I was not going to mess with the
engine for awhile.

Upon reinstalling the distributor, I had noticed the the rotor
locating tab was broken.

Being that I was not pressed to get this engine repaired for awhile....
I gave it no thought to why it was broke.... I just ordered a new one.
(which I forgot in time that I did).

Being that at that moment, I knew I had just ordered a new one
I thought I would try out this JB Plastic weld I had laying
on the shelf, to see how strong it was.

After a few days.... I was amazed at how it cured.
I gave it no more thought and installed it in the distributor
so as not to lose it....knowing a new one was ordered.

Well a month went by and Coty demanded that I install
his back up engine so we could make the family reunion
Mud Bog that was coming up.

The engine ran great all day long at the bog and
let go at the end of the day while shifting from
1st to 2nd at about 6500 rpm's.

Now after a few weeks... I had discovered the rotor I had ordered
and decided to install it before I forgot again about it.

That's when I discovered that the repaired rotor
had broke.

IMG_1142.JPG


After installing the new rotor... The engine fired up
instantly!!!

NOW..... THIS IS WHERE YOU NEED AN OPEN MIND.

I was convinced that the race engine blew up because of lack of fuel.
The calculations show that the pump was too small...
and the fact that I did not allow more fuel to be added under boost,
just reinforced the theory.. The engine leaned out.
ALL ON ME !!!!

For the last week... I have been thinking alot about how and
why that rotor had broke...

I have come up with a theory that almost might make sense
to me, and wanted to run it by you guys..


I THINK THE ROTOR HAD BROKE IN THE RACE MOTOR
AND CAUSED IT TO STOP RUNNING.

Now from the pictures above, it was on it's way out
anyway. But I think the rotor broke first before the lean condition
destroyed the engine.

My theory is: that the plastic locating tab is pushed down
into the plate in the distributor. This is a very thin
plate..basically sheet metal.;
and the locating hole was produced
from a punch and die .... This hole has a sharp edge
from the piercing .

The rotor tab is plastic.

IMG_1163.JPG

I am thinking that the force of that thin plate
was pushing enough on that plastic locating tab to
actually start cutting it's way into the tab...and eventually through.

Think about this.... If it did cut a slot in that rotor..
The rotor would actually advance itself from the plate
edge moving into it... ADDING timing .
Let that soak in for a moment..

Below is a quick sketch I made showing ho far the plate would
have to cut into the locating tab.. in order to move only 1 degree

IMG_1165.JPG




That would surly be a major problem under boost!
It would explain a lean condition too.

Ultimately the plate cut all the way through the tab
and caused the rotor to spin freely on the post.
Which is why the engine quit running.

I haven't measured the tab yet but I would guess
it to be .187 thick.

If so.... you could divide .187 by 0.026 and
find that it could advance the timing by about 7 degrees!!!!!!:eek::eek:

THIS IS ALL THEORY ... BUT A CUT ROTOR.... ?????
I feel this is not too wildly out of a possibility.

Would love to hear your thoughts on this theory...
 
I think we need some better pics of the broken area to really tell.

First impression is that it broke, if it was cut by the plate it would be straighter and cleaner cut.
 
My thought is ALL blown engines should run a magneto.

Slop in distributor gear could have caused the rotor to kick back and break.

My opinion on ring gap in a blown engine is the more the better--blow-by is expected. >045 will not be a problem unless you think static cranking compression will not be enough to get engine started

Fire (magneto) fuel (E-85) air (blower) compression (enough to crank) all will be enough if the fuel and fire is there with the magneto.

Heat is the number one killer of pistons and when the rings come together they seize to the piston or cylinder wall. Something will break--usually the piston which then cause other catastrophes.
I sometimes think major engine builders do try things to find out what happens--IF WE TRY THIS---WHAT WILL HAPPEN '? The average racer doesn't have that kind of money.

JMT
https://monstertruck.fandom.com/wiki/Grave_Digger
If you know of a Monster Truck guy personally, they might help you the most as they can make a truck run even if it is upside down.:D
 
I think we need some better pics of the broken area to really tell.

I fully agree Rick.... I will address this issue tonight.
Remember this is a theory I have cause I asked myself...
What caused the rotor the break in the first place.

More pics tonight.


My thought is ALL blown engines should run a magneto.

T... Brian had offered me a magneto awhile back.

The problem is that the Sniper's ECU is controlling the timing and needs the HYPER SPARK distributor .
It is a HALL effect type of distributor.

Slop in distributor gear could have caused the rotor to kick back and break.
Everything is BRAND NEW... so there should be no slop.
I am running the M77 BBC oil pump also, so that should make the gear smoother. (12 teeth in the oil pump gears compared to 7 teeh in a SBC oil pump)
I also checked the pump drive shaft for proper clearance.. it was great. I posted a pic of it earlier in the build thread.

Heat is the number one killer of pistons and when the rings come together they seize to the piston or cylinder wall.

This adds to my theory.. The distributor spins clockwise....so if there was a groove cut into the plastic locating tab..The rotor would technically
be advanced in the counter-clockwise direction because the plate (pushing on the tab to rotate it) would be further into the tab
before it could spin the rotor.

It would not take much at high RPM'S to melt pistons.

If I put a cutting torch over a plate of aluminum then pulled the oxygen trigger...It would almost blow through immediately ..

If you know of a Monster Truck guy personally, they might help you the most as they can make a truck run even if it is upside down.

Yes I do! Cory likes to give me shit (all in fun) about my engine..
He is trying to get me to switch over to alcohol.
He runs a modern 4.8 liter junkyard motor with an 8-71 blower on his personal toy. I laid my hand on the blower
and thought I had instant frostbite! Says he pays only $3 a gal..
 
those boys are WAY out of my league.

but the part where he explains that this type of engine is way different than a drag car engine holds true.
A drag car is in the throttle for about 10 seconds or less, where a truck is in the throttle upwards of a couple minutes.
Building HEAT.
 
Having a problem understanding how rotor broke. It had to have force in two different directions to break. Only thing I can come up with is vertical movement of rotor allowing it to hit baseplate?
 
Me too!
The only thing I can come up with is ...the rotor sits and spins on a shaft. It is driven by the tab at the bottom of the rotor, which is seated in a slot.

I am thinking that maybe the rotor somehow got seized some what enough to cause friction inside the rotor and the plate .... well it can't stop spinning.

It is all theory.... But the only FACT that I have is that the rotor locating tab was snapped off somehow.
I am just looking to understand WHY....

Yes ... it makes sense that the rotor could have had to much down pressure on it and maybe caused it to bind enough on the shaft
to allow the base plate to snap off the tab... I will take a look at the inside off it tonight also...

I'll get some new and better pics tonight....hopefully between us all we can figure this mystery out.
 
Well...looks like I can only speculate now.
The wife has a rule in the house.....Anything left on the counter top for more than
3 days either gets tossed or shelved in another place of her choosing.

Being that it was about 3 weeks ago when I replaced the rotor with new....and brought the old rotor pieces into the house
to show her....I sat them on the counter top.... YEP...she tossed the old rotor!
Says I did not need to keep junk.

I just have to chalk that one up with they other dumb mistakes I have made.

What I think I may do though... I will wait until Friday or Saturday morning, when it's not so hot out
and remove the cap and rotor from the backup engine that is in the truck.
I can then use dial calipers to measure the rotor tip to the cap base on the distributor.
Then measure the distance from the bottom of the cap to the brass terminals.
This would at least show me if there is any interference.
I could also check center pin for excessive up and down play too,
but I would think the plunger in the cap is spring loaded... it might be bound putting too much pressure on the rotor too.
May sound like I'm reaching...but it can't hurt.
Another thing John got me thinking about is....binding.
I recall the base plate had a coating of surface rust on it
when I put the new rotor on.

The engine is prone to have water spray some what get on it
because of the environment it operates in... Maybe the shaft that the rotor spins on has just enough surface rust
on it to cause the rotor to not spin freely ...... That would make the most sense at the moment.
 
I would call the HYPER SPARK distributor provider and tell them what happened and see what they say. Distributor shaft bounce could be the culprit as the rotor spins the hall effect plate that might have been loose or have a rough spot to hang on shaft.
 
Timing will not be changed if the rotor moves, but the spark could jump to the next (or before) cylinder. You need to move the trigger to advance or retard timing.

Now on to something else, I have problems with belt slip with my 177 blower, if i ease in to throttle it makes boost, but if i mash the loud pedal (kickdown) it makes hardly no boost, how much tension do you have? My tensioner rest in the middle, seems ok?
its a 10 rib belt.
 
you have the same belt I do...I have about 85-90 percent tension in the slot.
You may need to coat the pulleys for more grip or your belt may be worn out.
My belt measures 52"
Also, your spring may be weak on the tensioner.
 
Could the motor have hit the firewall? The cap could stretch the hold down springs and allow the rotor to hit the contacts! Check for damage to the cap.
 
Could the motor have hit the firewall? The cap could stretch the hold down springs and allow the rotor to hit the contacts! Check for damage to the cap.

NO.. That was the reason for removing the cap before I pulled the engine. I did it for that exact reason.
When I did pulled the engine, there was more than enough clearance. I just wanted a safety net.
 
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