bjr48

I'm getting some microscopic craters on my head. Now I know I accidentally got a few grains of dirt in this engine at one time and cleaned it out. I saw signs of specks on the head and piston top and side at that time.
Now I've got about 2 gallons on it and am seeing more specks on the head. It has run a little hot a couple of times due to a cracked fuel tank and other minor mishaps. But now I am wondering how to read the fine details and how to react.
From what I have learned, damage to the head would be caused by:
1) too lean
2) too much compression
3) dirt
How do I tell the difference? I am assuming that compression would always be followed in hand with a distorted glow plug element? Dirt would show up as damage on more than just the head surface? And a few times too lean would show up similar to the compression issues minus the glow plug distortion? Or do the marks on the head look different for each one? I've got a 10x eye loupe to check it out up real close so what do I look for??
I guess what I am asking is if I am sure I have no more dirt in there how do I tell the difference between a temporary issue like a few lean runs causing damage that if I be careful tuning will get no worse and a long term problem like too much compression that I should make a permanent change for with a shim?
I'm getting better and have read the articles for a long time now, but I always have trouble applying it myself in real life

Adim_X

iTrader: (16)

THe motor is pre-detonating. You are more than likely to lean on the needles. Make sure it is shimmed correctly and that you are using the right plug for your area and fatten up those needles a tad.

Zerodefect

If your talking about the type of specs I think you are, its probally a little detonation, alltough thats normal wear sometimes.

Niether the piston or the head are really made of strong materials. Pretty soft stuff. Most engines with 9+ gallons of racing that I've seen have had some specs on the piston or head.


What engine, fuel, glow plug, carb insert are you running? What heads shims? Stock? What car? Pipe? Clutch setup?

Maybe its someting obviously mismatched?

speedy2

iTrader: (1)

I would say it's dirt particles passing your airfilter all the time
or you didn't get them all out cleaning the first time
check that out first
are you changing it regulary or are you racing on a dusty track ?
bearing failure can be the problem too if you get bigger craters, but then it's already to late..

bjr48

I change my air filter every practice or every other practice. No racing this year.
I inspect the engine after a couple of practices usually or sometimes every practice. I do know that there were a few pieces of dirt that I let in there accidentally early in the season that didn't get much run time after they got in. I think I changed a plug at the track or something ran a little then found the damage at home that day. I tried to take pictures then but they didn't really show the detail I hoped. I'll try and dig the best one out and take a quick pic of what I've got now and maybe someone will catch on becuase I'm not.

I am running Kyosho MP-6 with OS vg21 motor stock, 9886 pipe with long header. 1st 2 gallons were Odonnnel 25%. Now I am having trouble getting fuel so I burned up about 2 tanks of some Trinity Monster 30% and had to run a quart of 20% Odonnel this last Saturday. But I've re-tuned every time and kept temperatures between 200-240 typically. With the fuel tank leak, yeah at the end of the tank it creeped up to 280 but it wasn't WOT or for more than a lap. So all of the new damage may just be lean running and it's minor. But I want to make sure it's not being caused by too much compression so I need to know how to read the engine.

Also if it's minor should I smooth it out some so I can find new problems or just leave it. I know that you will need to see the pics first!

speedy2

iTrader: (1)

could be a coil from the changed plug that failled
and found his way into the engine
all you can do is clean the engine thouroughly
if you think it's necessay, and go on

bjr48

It definately was not that. The plug was just changed becuase it was old and not running good enough for me so I pulled it out. No missing coil.

bjr48

The pics won't turn out right to show the details. All of them look like the engine is brand new!
I'll bet the recent additional marks are from lean running becuase of my tank leak. And my fuel came in so I don't think Odonnell 25% on the stock OS shim should be a problem. I'll run that the rest of the year now. The book says run up to 30%.

So if I feel that it's tuned right and always have enough smoke even at WOT and get more marks is that a sign for adding a shim? At that point would the plugs be distorted or does that just depend sometimes? I don't think based on what I see that I need more shims. How do you guys know??

Otherwise it's probably a little lean, right?

jamiekerr14

Just wondering, When you changed from 20% to 30% Did you add a shim at all.. as to me that could have been your issue. Pre-Detonation but Im no guru on engines.

bjr48

Could be the problem. When I ran the 30% I only had enough for about 3 tanks so I didn't do much to re-tune. It looked OK by smoke
OS manual says up to 30% so I don't know.
I've ran 25% since I started that engine for the first time because I was in the habit of sharing cases of 25% last year with a buddy at the track that was running an RB engine which is shimmed stock to run up to 25%.
This post it pointless without pics. As I read back through all of my rambling I really just want to figure out how to read the engine for signs of too much compression vs. lean or both I guess Either way I made a slight mistake. I'll be able to figure it out the hard way too I guess! Thanks for all of the suggestions...

griz11

Those pock marks are from detonation. The piston is now useless. Those pock marks will glow after a bit of running and continure to screw up the timing and create more pock marks. An engine that is running hot will have a dark deposit on the inside of the piston. When they get that way that piston is toast also. When you went from 20 to 30 you advanced the timing unless you reshimmed or changed to a colder plug. The amount of nitro in the fuel partially determines the timing. The amount of compression plug heat range and % of nitro all combine to give you the engine timing. The plugs will generally be distorted a bit toward the exhaust port. Usually they are pushed toward that side so the coil no longer sits in the middle of the plug. If the pock marks aren't deep you can sand them off with fine grit wet paper. Mostly its the edges that are sharp that can create the hot spots to cause more damage. Air temp humidity and atmospheric pressure also play a part. While there are a lot of variables to cope with I suspect when you went to the 30 you detonated.
Griz

bjr48

This may be true since the 30% was run for only two tanks and not much tuning seemed to be needed. However with all of the air leaks through the fuel tank I was dealing with isn't it more likely that all of the damage was due to way too lean erratic running from intermittent air leaks I was tracking down and dealing with? Lean conditions from air leaks would cause the exact same damage right?

MAIN POINTS THAT STILL ARE FUZZY:

So plug wires can be distorted BOTH because of lean running or from just too much compression?!

You can run too much compression and not be lean right? Just detonating.

And the marks can be caused by JUST being lean and that would cause pre-detonation, right?

I don't understand why I never picked up on the difference or if there is a difference. Please someone set me straight.

bigde2001

iTrader: (10)

Add a shim. See if it helps.

keavze

above answers are best to my humble knowledge.
please correct me if i'm wrong.