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  1. #1
    RC Champion olds97_lss's Avatar
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    Cracked crankcase's, 3 and counting...

    Am I the only one constantly busting crank cases in their jato? I had a 18TM in my jato last year, cracked the crank case at the ear where it mounts, more than likely due to a roof landing.

    Now, in a matter of a month, I've cracked two more. Neither by roof landing. I had an old 2.5 and ran that for a the remainder of last year and a month or two this year (total of 3 gallons or so), then it started acting up and didn't have compression, so I got a new 2.5R. Ran great, probably got half a gallon through it and all of the sudden it started running horribly. Then I noticed the oil all over the chassis and again, a busted crank case. So, I swapped out the parts with the old 2.5 and ran it the past couple of weeks. Being afraid of busting yet another crank case, I cut the top 3 fins off the 2.5R, even though I know I didn't land on the head the last time. Just trying to avoid it altogether.

    Out running today (temps around 230-240 for about an hour) and it starts running bad again... sure enough, cracked crank case.

    Now I know for a fact that the last two did not crack due to impact of the engine directly, so what is breaking them? I've ordered a new one, but I'm at a bit of a loss.

    Here's a photo of the line between the roll bar and rear tower:


    And with the head cut:


    And the latest crack...


    Anyone know what's going on? They've all broken the same way, the rear engine mounting ear.

    This time I'm going to try and put a thin layer of rubber under the ears and on top of them to help absorb shock from landings. At this point, hard landings are the only thing I can think of that are causing this. Although, I have a feeling that putting rubber on the mount will bring my temps up due to isolating the engine from the mount/chassis since the entire chassis is a heat sink. Also I'm concerned with keeping the bolts tight since it will be not "tight" due to the rubber.

    If it breaks again, the only other thing I can think to try is to create a dam under the engine and put a pool of epoxy in there, then mount the engine and let it cure. This way the engine is supported by the entire crank case vs just the two ears.

    Kind of at my wits end here. What really stinks is that out of my 3 RC's, the jato is my favorite to drive!

    Anyone with any suggestions, I'll be glad to listen. This is getting expensive and frustrating. The internals of this engine haven't even gotten a gallon on them yet and I'm getting yet another crank case!
    Expert rigging at it's best!

  2. #2
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    My 3.3 is crack at the mounts also and I only run my Jato on-road. However, it’s still running strong don't know for how long though. I just figured that was the engine weak point.

  3. #3
    RC Racer
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    You dont have to land on the roof to crack the block, I managed to crack mine by flipping it backwards while attempting to wheelie. Anyway the stock roll bar does nothing when landing on the roof, it just bends until the head hits.
    A sure cure for seasickness is to sit under a tree

  4. #4
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    yeah i cracked one just by flipping it my FIRST TIME out
    Confused rcer

  5. #5
    RC Racer
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    Is it possible that the chassis is slightly bent and putting additional stress on the case when you're tunning? I've been running my jato hard for years and never had a crankcase crack. I could just be lucky - but I have broken a couple of rear shock towers, busted my pipe, stripped the tranny, and once smashed the whole truck head-on into a concrete block in 2nd gear. The entire front end was obliterated but the engine was fine.

    That said it could still come down to luck, especially if so many other people are having the same problem

  6. #6
    RC Champion olds97_lss's Avatar
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    Well... I'm now on crankcase #4...


    Tried putting a bit of rubber sheet under the mounts and tightened the engine bolts down snug. Was a pain getting it installed since it made the mount a bit taller, but to no avail... busted the same ear yet again.

    Feels like it's time to shelve this thing. Between the time/effort and $, I can't make it a bash session without costing me a new crank case.

    The only thing I can attribute this to now is slapping the ground on landings. I didn't wreck a single time today, but I did land from about 3-4 feet on concrete. I ran 3 tanks of fuel...

    I surely did not go through crank cases like this when I ran revo white springs on the rear. Guess I'll have to go back to them as that seems the only possible problem now. I'm running cut UE Red SuperMaxx springs on it now which are I believe around 12lb springs. Stiff enough to not slap the ground off of a 12 inch drop, but soft enough to run over rough terrain without bouncing.

    I have one more crank case... I just don't know if I have the patience to tear the stupid engine down for a 4th time. If I do, I'm going to make a pool of epoxy under the engine mount for the bottom of the case to sit in. Hopefully to give it more support. It seems that since it's cracking on the lower side of the ear, that it's from landing and the engine is dropping. With epoxy holding the base of the crank case up... either the entire crank case will crush or it will work... or some unforeseen thing will happen. That with the stiffer springs might make me through a single bash session at least. I just hate running the stiff springs...
    Last edited by olds97_lss; 09-27-2009 at 11:09 AM.
    Expert rigging at it's best!

  7. #7
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    Could it be how you are mounting the engine? For example are you using stock screws, or screws too tight..etc You shouldn't be on your 4th case in that short about of time.

  8. #8
    RC Champion olds97_lss's Avatar
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    Stock screws. Hand tightened. Stock chassis, stock mount... non-stock items are things not related to the engine. Servos, arms, wheels/tires, shock springs, pipe, header.

    I tore it down, cleaned everything, replaced the crank case with my final spare, created a little dam out of tape, then put about 1/4-1/2 inch of epoxy in the recess and dropped the engine in and bolted it down. It's now curing. Now that I'm thinking of it... I should have put a coat of oil or something on the chassis so it didn't stick. Oh well, will see how it does.
    Expert rigging at it's best!

  9. #9
    RC Racer
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    Just out of curiosity, are you using the spacers on top of the engine mount?
    A sure cure for seasickness is to sit under a tree

  10. #10
    RC Champion olds97_lss's Avatar
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    Sorry, I missed the email notice for this thread.

    No, the spacers are underneath where they are supposed to be.

    The epoxy didn't cure right, too old or bad mix, not sure which. I cleaned it out and used the same damming method with JB weld instead. I also switched my rear springs to 1/8 buggy springs that I had from my UE maxx shocks. I had to cut the springs to length. They are stiffer than jato stock, but softer than revo white (which I had ran in the past).

    With those two changes, I got a couple bash sessions in without issue. Although, I was mindful about the jumps I made and kept them under 2 feet.
    Expert rigging at it's best!

  11. #11
    RC Turnbuckle Jr.
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    Its a week spot. i have broken 1 that way. I went under a car on axident going full speed and it riped them out. It was all caused from a bad brake disk
    No more money for rc trucks I got 1:1 truck

  12. #12
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    looks like the machined flat spot has a 0 radii. this makes a high stress area. if you could get it re machined to a .06 rad. that might help. how ever it will change the hight of the mounting spot.

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