Engine cradle reinforcing

Message

m_mcgranahan · #1 Post by **m_mcgranahan** » Sun Jun 24, 2012 12:22 am

Hi,

So my current engine cradle wtarted to crack in front of the solid piece that the engine bolts to is welded to the horizontal bars. Here is what I have come up with so far.

http://sports.webshots.com/photo/2630172700032235899RxyxXF

haulinit · #2 Post by **haulinit** » Sun Jun 24, 2012 3:28 am

Mine also cracked there just on the other side of the bracket.

m_mcgranahan · #3 Post by **m_mcgranahan** » Sun Jun 24, 2012 1:12 pm

Yeah, I think they crack on the chain side as teh torque of the motor pulls forward on the chain, it pulls back on the motor mount and causes the crack to form in front of the upright. I figured if the upright had support behind it, it would be less likely to be able to pull back hard enough to get that crack to reappear.

m_mcgranahan · #4 Post by **m_mcgranahan** » Sun Jun 24, 2012 8:41 pm

I was thinking about putting a piece in front of the verticle piece to, but there doesn't seem to be enough room for it.

rayspeed · #5 Post by **rayspeed** » Sun Jun 24, 2012 9:16 pm

I see them crack mostly in front of where you put that gusset... between the upright of the front engine mount and the battery tray on both sides. I have ground out most of the crack and had luck with welding the entire length of the battery tray where it is just tacked to give it some more support.

m_mcgranahan · #6 Post by **m_mcgranahan** » Mon Jun 25, 2012 1:09 am

QUOTE (rayspeed @ Jun 24 2012, 09:16 PM) <{POST_SNAPBACK}>

I see them crack mostly in front of where you put that gusset... between the upright of the front engine mount and the battery tray on both sides. I have ground out most of the crack and had luck with welding the entire length of the battery tray where it is just tacked to give it some more support.

Hi Ray,

Yep in front of the gusset in where mine cracked also and I am convinced that it cracked from the constant rearward pull of the motor/chain causing the verticle piece to flex backward adn leading to cracks in the front of it. (Most materials are stronger under copressive load than under a load pulling on it) So the reason for the gusset behind the vert piece is to keep it from flexing rearward ad cracking in front of where it is welded to the horizontal piece. I like the idea of also welding the batt tray more fully

GOd bless...
Mark

Canniboomer · #7 Post by **Canniboomer** » Mon Jun 25, 2012 6:11 pm

I have found that the main cause of the cracking is the huge amount of pre-strain at the front cradle brackets, where they draw out against the frame ears when bolted up.... More than half of all machines could use some critical shimming on either side you choose. Everybody should check their machines; remove either the 2 right or 2 left front bolts, and pre-check that the opposite side bolts are tight -- then check for how much "GAP" exists -- some of you will be amazed. Then use 5/16 or 8mm washers to pre-shim up there. Our cradles are very stiff, and the front ears don't want to stretch wider. And the frames ears don't want to flex inward either. But some machines have more than 1/16" of gap up there!, for an intense amount of stress after bolting tightly -- if not shimmed first. The rear attachment does not matter, since the longer extensions back there will flex out easily

wistech · #8 Post by **wistech** » Mon Jun 25, 2012 7:13 pm

I agree with Boomer on shimming the front case and mounts so nothing is squeezing or pulling the gaps together when the bolts are tightened down. There is already enough internal stress from the shear amount of welds in that area .

MX Quad Dad · #9 Post by **MX Quad Dad** » Wed Jul 04, 2012 12:17 pm

Other thing I would watch is chain adj. if you are doing it according to the manual, it is to tight. I think wisetech explains the adj. process best. Use tie down strap from axle to grab bar and bring it down till chain is at its tightest point (should be when center of axle, swing-arm bolt and drive sprocket are in line) then make sure you have some slack.

If you think about the engine torque or even the over tight chain theory. you would need to have a lot of play in the swing-arm bearing or bolt flex to transfer the movement all the way to the front mount. so boomers theory seems to hold the most weight. it doesn't seem to be a bad idea to re-enforce it since it was broke, but remember you may be just moving the stress point and stiffening it up to possibly make it worse. plus the welding may make it pull and give you even worse clearances.