Xflow Piston Issues

[Laker]

What has caused this? The motor ran great! It really liked to scream at the rumble! It still has 130 psi but the plug looked dirty so I took the head off. Timing is 26 degrees. 67 main jets. Is this overheating? the other 3 looked perfect. Any Ideas????

[84exciter]

DELIVERY,AND TIMING AGAIN.THEN FATTEN HER UP.LOOKS LEAN

[dan agnew]

can you say detonation???
looks a smudge lean to me. more race fuel or more jet OR a little less timing. i myself would up the fuel ratio first but it looks like it may already have started the kill. pull the side cover and look at the piston skirt and the side of the piston. if it is scuffing pull it.
what does the intake side of wall look like?
guess the ports are flowing a bunch huh??

Danny

[Laker]

hmmm
the plugs looked great on a Top end check and the other holes are running well... Should I run a 69 in that hole or all of them? I have been doing the primer check all weekend also and the motor was slowing down with the primer on. The intake is not scuffed at all but the top is kina crusty. I still think I should change out the piston. Will give me a chance to make other changes anyway.

[woodco]

Did you pull the other head ??? That does look a little lean to
me ......

[Laker]

Yep
The other side is Fine.
I know #4 likes to go in the V4 first....

[Charlie M]

What kind of gas where you running. Most of the time I see this generally I find a fuel restriction, loose fuel line (sucking air), or not enough fuel supply to the motor. It can also be not fat enough on the jets. I see insuficient octane gas do this alot, but I think with 130 psi on a crosscharged 93 octane is more than enough as I have run 165 with 28 timing on corsscharged motors before.

Also that the motor is slowing down with the primer, I would check fuel delivery sounds like your running out of gas. If it where a jet issue the motor would pick up the speed. If you has someone pump the primer ball while it was running you could eliminate this.

Charlie

[Laker]

2 gallons of 112 and 4 of 93 mixed. 67C mains, 35 low speeds. 32 to1 Penzoil synth. Air temp was mid to high 90s as everyone at the rumble can attest the Humidity was also Very high. New piston and Fatter jets... Once I get her torn apart Perhaps I will find somthing.

[Charlie M]

Is this why Delaware Rick was able to keep up with you.

Make shure when you put it back together that your fuel delivery system is all OK.

On of the sleeves spun in the block of the Big Johnson, the ports are half blocked off. I have to get it the rest of the way apart to see what happened.

[thumper]

At a great price. It's sitting on my shelf getting old, call me.

[Laker]

Hey buddy!
Great to meet you at the rumble!!
Shoot me your number and I will call you tomorrow
Chris

[Laker]

The Carbs I am running are 1978 140 1 3/8th carbs. They only have 2 circuts High and Low where the later V6 carbs have low, medium and high circuts... What is the better setup? These cabs worked great on other motors but none that have flowed this much.

[Jeff_G]

Don't overlook a small water leak as well. It could cause the muddy look. What do the bores look like? How about the domes when you clean the crud off? Check your lower seals as well as long as you are pulling the powerhead.

[Laker]

Yep I am thinking like you are also.... THis motor is 3 weeks old with new everything but the crank center main is less than perfect... it has about 75 gallons of fuel through it at this point and Ran pretty well overall. I have never seen a piston do this .... eat away the intake dome like a sand blaster! They allways seem to just nuke out white or over heat..... or scuff and squeek..
Kinka a new one to me. I ran over 25 gallons of fuel at the rumble where his happened so Im still going over everything just to make sure before tear down. Im looking for where #4 could be sucking air

[dan agnew]

mike said in your phone call the other day that you said that you changed elevation and that may have also helped. i think you still just a little lite on octane. you may try and up that jet a bit but not too much. you are close. also how much did you run in mid range? very much?
if you operate in mid range very much you may want to try the newer carbs. more to mess with but a little better adjustability thru the full rpm range.
i still think you were just a touch lite in octane and i know you do not want to give up any timing. as i told bl if i had the choice i would lose a small amt of compression to keep up the timing but if you are already running 104 or better then just up the 104 and down on the 97.

Danny
something else to consider look at the exhaust downstream of the adapter as you may be backing up the flow and causing a hot piston top

[B.Leonard]

We know that cyl got real hot.

I'm wondering, was it hot to start and then the jetting, gas or timing pushed it to burn?

What kind of water psi were you seeing?

When my V4 burned #4 it happened when I uncovered the water pickup. It had run for years with a much heavier load before then.

The primer trick will only work for gross fuel starvation. A motor will run the best (most power) slightly lean. Hitting the primer will cause it to slow and you'll think "I'm rich" when in fact you're on the edge and just waiting for something to push you over (ie bad gas, low water psi etc.).

I have learned (with 2 cycles) that by the time the plugs have enough runs on them to be confidently read, it's too late engine damage could've been done. I would make a mild pass (make sure your into the main jets, but not WFO) and then read the piston tops with a bore scope.

-BL

[racer]

TOO Lean. I would switch to latter model three stage carbs. Many times these engines will burn at partial throttle and on decel the latter carbs will help. Also I would look close at your head gasket the block shows a different color at the top edge of the sleeve like it might not have sealed completely.

[wolfgangb]

TOO Lean. I would switch to latter model three stage carbs. Many times these engines will burn at partial throttle and on decel the latter carbs will help. Also I would look close at your head gasket the block shows a different color at the top edge of the sleeve like it might not have sealed completely.

I am aware that this is an old thread. However very interesting to me because I am in the process of planting two 235 hp OMC carbs on a 103 ci Force 4 cyl motor.
I concur with racer. Plus: " the Humidity was also Very high" - there there is water vapor there cannot be any (cooling) fuel. The head gasket surely pushed it over the edge. I was a Chrysler mec in Germany in the mid `60s. We had lots of these failures on the 105 hp motors, till the advent of better head gaskets (we worked with Reinz on that one).
Rgds,
Wolfgang (South Africa)

[powerabout]

I am aware that this is an old thread. However very interesting to me because I am in the process of planting two 235 hp OMC carbs on a 103 ci Force 4 cyl motor.
I concur with racer. Plus: " the Humidity was also Very high" - there there is water vapor there cannot be any (cooling) fuel. The head gasket surely pushed it over the edge. I was a Chrysler mec in Germany in the mid `60s. We had lots of these failures on the 105 hp motors, till the advent of better head gaskets (we worked with Reinz on that one).
Rgds,
Wolfgang (South Africa)




High humidity makes the air less dense so easier on the engine or you can run more comp.

[perfmarine1]

2 gallons of 112 and 4 of 93 mixed. 67C mains, 35 low speeds. 32 to1 Penzoil synth. Air temp was mid to high 90s as everyone at the rumble can attest the Humidity was also Very high. New piston and Fatter jets... Once I get her torn apart Perhaps I will find somthing.

You're running way too much octane here is a good chart503266