Huge Problem with front Engine mount...

Discussion in 'Frame Mounted Engines' started by JohnnyLoves, Jun 5, 2008.

  1. JohnnyLoves

    JohnnyLoves Member

    Help! Huge Problem with front Engine mount...

    Soooo, my dax70cc vibrated itself off the front engine mount today. Basically the bolts and plate were still intack and it just popped itself off the threaded studs. Originally I thought it would be a nice simple rescrew, but after I looked at the engine it turned out to be much worse. The threading inside the engine mount block is completely stripped, and small portions of the aluminum are missing. It looks like the studs took some of the engine with it when it popped out.

    I dont know what to do from here. I've thought about just trying to loctite the studs back, but I dont know if that would be a good solution. Welding the mounting plate to the engine block? Really in a jam here fellas, this bike is my major form of commute.

    John
     
    Last edited: Jun 5, 2008

  2. datz510

    datz510 Member

    Mabye try some JBWeld to set the threads back in the block?

    Also, you could try chasing the threads with a thread tap.

    If push comes to shove, you could simply drill the hole out slightly and tap it out to the next larger metric bolt size.

    JB weld would probably be a good temporary fix for now.
     
  3. fastboy9

    fastboy9 Member

    I'm fixing the exact same problem at the moment but with my rear mount. I First got some epoxy putty, the hardest one possible, its called steel putty or something like that, I'm pretty sure JB weld is the same, it must be hard enough to be tappable though; this is very important. Then with the putty I crammed it into the hole on the engine block and smoothed it over flush to the engine block. Next I drilled a 4mm hole into it, and next used a 6mm tap to cut a thread into the hole. Next I brought myself some high tensile M6 bolts and loctited them into the new thread.
     
    Last edited: Jun 7, 2008
  4. Irish John

    Irish John Guest

    I think it eventually happens to all the mounts at some point. Steel studs into aluminium is never a very good grip and the casing around this stud is very thin at this point. The usual thing that happens is the studs snap off just where they join the engine block. It's a problem because I think the only good fix is to ditch the present arrangement and rethread the hole to a larger size which would be 8mm cos the original was 6mm. If you can get 7mm bolts that would be better cos there is very little room to play with here. 8mm would take you dangerously close to the edge of the engine casing and thus risk it cracking itself right off. I've done 8mm on the rear but there's a bit more room to play with there. The front studs are the worst ones to fail and I think I'd seek the expertise of a good metal workshop that knows about aluminium alloy etc. They might put some globs of alloy into the damaged bolt holes and be able to rethread the hole through the new alloy to take the original 6mm bolt or stud. I strongly recommend the mounting method shown in the attached pics because the load is more evenly distributed between the two 6mm nuts and the whole motor is held by an 8mm dia hard steel bolt through the downtube as you can see in the pictures. Definitely use 8mm and not 6mm for the through tube bolt - that's critical. This is an alloy downtube and has done 13,000 kms on 4 HT motors without a front mount break ever and no cracking in the downtube. Use a few big washers on the other side for added strength. The 8mm bolts don't snap like the 6mm ones and this is one of the big design flaws with these motor mountings. Don't use Chinese bolts, nuts or studs. Get decent US hard steel ones made to proper international standards. If you remove the motor and take it to a good metal guy he shouldn't charge you more than a few bucks. If they quote more than 15 bucks I find crying helps and saying "what am I going to tell the kids?" in a pathetic voice often does the trick. I hope it works out for you and I think the method I've shown will give you a stronger mount but then there is the rear mount to think about! Good luck.
    Oh yes, use blue loctite on steel threads into aluminium.
     

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    Last edited by a moderator: Jun 7, 2008
  5. JohnnyLoves

    JohnnyLoves Member

    I like how you took the bottom front motor bracket and turned it upside down to give it a better fit to the larger downtube. This seems much better than the flat 3 hole adapter plate that is normally used.
     
  6. Irish John

    Irish John Guest

    The normal mounting method involves too much pulling on those short studs and I feel that the longer the stud sticking out the greater the vibration affect etc. so using bolts instead of studs seemed a better option and then it allows you to use a bigger stronger bolt through the middle of the tube to take most of the load. I found from experience that when drilling through downtubes I drill 2 holes from each side rather than one hole straight through cos it's easier to stuff up the line of the holes doing it in one drilling rather than two separate ones. This method also worked well for my Schwinn cruiser which needed an extra engine block spacer to reach the downtube as shown in the picture. I considered using the central through bolt on the rear mount as an extra support as well as the usual two bolts but it would require an extra rounded mounting bracket and the holes would have to be drilled exactly after it was mounted and then it might be almost impossible to remount the engine because you need some play when mounting to get the centre bolts to go through. You can see I considered it from the hole drilled on the rear mount photo but gave up because it seemed too hard. I've also noticed that the rounded mounting brackets on the HT vary in quality - some are thick and strong and some are thin and flimsy. I've had to send a lot of thin ones back and ask for thicker type ones. Since I got the 4-stroke I must say I don't miss these mounting problems but the Grubee tray still uses steel threads into aluminium blocks which is totally unforgiveable given that it isn't necessary on the 4-stroke. These guys who design the details either mustn't ride motored bikes or must be a bit thick.
     

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  7. wayde

    wayde Guest

    maybe this pic will help a bit, it's quick cheap and easy then you could pull off the rear center bolt
     

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    Last edited by a moderator: Jun 8, 2008
  8. JohnnyLoves

    JohnnyLoves Member

    I'm probably going to need a new engine : / The JB Weld isnt holding the bolts in, unfortuantly it's cracking. This whole situation is terrible considering I havent had this engine for more than a month.
     
  9. datz510

    datz510 Member

    Don't scrap the engine.. If you have a drill, drill out the hole so you can tap it for the next larger size bolt. Tap and die kits can be had cheap if you look around. They are pretty easy to use as well. With some cutting oil, a cold beer, and a few minutes of time that bolt can be as good as new.
     
  10. fastboy9

    fastboy9 Member

    I've given up with the JB weld now too. Just not holding up as well as it says it will. I've had to re-tap the rear mount to M8 now because I cant find M7 bolts anywhere. The front mount most likely wont be able to go as big as M8 though as there is very little parent metal to begin with, so you don't want to push it too far.
     
  11. JohnnyLoves

    JohnnyLoves Member

    unfortuantly, I cant drill and tap because theres really no parent metal left....when the bolts sheered off it broke large sections of female end the bolt screws into off with it : / I thought if I put JB Weld in and drilled and taped that it would be fine....sadly, the JB Weld pulls right out when I bolt the mounting plate on. Any ideas? or is this thing scrap metal?
     
  12. crabdance

    crabdance Member

    bummer johnny... hope you can salvage something out of all this. What a drag man. My heart goes out to you.
     
  13. JohnnyLoves

    JohnnyLoves Member

    Just a lesson to be learned crabdance, these engines aren't built to the highest standards, no matter who your vendor is...all made in China....
     
  14. crabdance

    crabdance Member

    I see, johnny. Yea, they are all made in China all right. I just don't want something like that to happen to ME!!!... ouch that must hurt. Have you decided what you are going to do? I hope that you get something out of the old one even if it's just parts. Maybe you can get you a new one and it will be better. My engine will be here in 2 more days and I'm terrified that something may happen to it because I have to put it together and I don't trust myself :).
     
  15. JohnnyLoves

    JohnnyLoves Member

    hmm I'll probably order a new one, I've give the JB Weld one last shot and if it doesnt hold this time, the heck with it.

    The best advice i can give you is, go slow, make sure everything fits without having to "macgyver" anything, and ask questions. It can take you 2 weeks to put one together like this, but in the end, nothing will fall off : )
     
  16. crabdance

    crabdance Member

    Thanks johnny... don't worry about me asking questions... I will probably start my own build thread. I will need all the help I can get. Good luck with the JB weld. I will keep my fingers crossed.
     
  17. mcassMB6

    mcassMB6 Member

    dude....was it the vice grips? JK...so sorry to hear all this went down. Just glad you did not get seriousy injured.
     
  18. WELD IT ARRRR!!!
    YES!
    Just WELD IT ON THE FRAME!!!
     
  19. Ok heres some pics of my not so well engineered fix, dont laugh to hard at my bush mechanics lmao, ok mine has never actually pulled the threads completely out, they are not real good to start with and from the first "fit up" I chased the threads and replaced the studs with M6 grade 8 socket head set screws.
    This bike does around 250 km a week and once I got stuck, pedaling it 20 km holding the clutch in and the extra weight sux, so I check everything when I get home from work and refuel, I have had the motor out a few times, (high maintanence of the whole bike keeps it going and reliable), and the mount threads where getting close to pulling so I jumped the gun and did this before they did.
    First I choped of the lump where the magneto wires come through and filled the hole, then redrilled almost at the bottom to reroute the wires.
    I then choped of the front mount so it was flat and drilled 3 6.5mm holes from top to bottom.
    Hopefully the pictures tell the story, I'm finding it hard to put into words, lol.
    Anyway I dont have time to make this bike or the things I have made for it look good, I make it work and keep it reliable and its paid for it self over and over.
    Cheers Phil...
     

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    Last edited: Jun 10, 2008
  20. Oh I forgot to add that on the rear mount pad there is just enough meat for M8's, but I am working on another way to mount it at the moment.
    I know from what I have seen on this forum some of you guys do some killer work, there is enough meat on the front mount to do what I have done and its as solid as now, I'm sure somone here could perfect it.

    Phil..
     
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