Engine Trouble Omg

[Bgard]

New here and have read a lot of the posts. I have a grubee 66cc Skyhawk just on the verge of being broke in. Today I decided to hammer a bit on it and it did really well for awhile. Then I noticed it loosing rpm so I backed off and let it go to half throttle. Ran great. I hit it again and no go. I pulled over to check it out. Looked at the plug all fine nice colour. Piston was good no scaring on the walls. What happened?
Upon investigating I found the problem. The rear motor mount sheared off the bolts and was letting the motor tip enough so that the drive chain would rub on the housing. the more throttle the harder it would rub. I guess when I read on a post to replace all those china bolts I should have taken the advise. Oh well off to the auto supply tomorrow.

 

[bluegoatwoods]

It's a bummer.

But you noticed something was wrong, you investigated and you found your trouble and figured out the solution.

You oughta do fine.

 

[Big Red]

When ya put the new ones in make sure the mounts are FLAT against the frame. If not the bolts will pull at an angle and bend them. This will lead to bolt failure almost every time. Whatever it takes to get the mounts flat on the frame.
Big Red.

 

[HeadSmess]

tis why i like welding the mounts on and replacing studs with unbrako's.

easy fix at least

 

[Big Red]

Yup HeadSmess,Welding the mounts in is probably the best way to do it, But most people don't have a welder or access to one. And even welded in ya still gotta make very sure it mounts up FLAT. Some don't realize how important this is. I've seen too many mounts at angles with a corner edge digging into the frame on one side, And a big gap on the other side. A newbie might think this is OK if the engine feels tight. They don't realize the mount studs are bent and the mount block is digging a hole in the frame.
We always stress how important it is to get the engine tight and straight, But not too much is ever said about the mounts themselves. A badly installed engine mount WILL lead to stud failure and possibly frame failure.
Big Red.

 

[HeadSmess]

oh yeah. this is true. important to get the rear mount as square to tube as possible, and shim or file away any gap on the front. at least it works better that way for me. i guess you could file the rear just as easily get max contact between engine and frame.

then theres always a bottle rack lug or a derailleur clamp in the way, that needs weasling around!

 

[Bgard]

I guess I should have mentioned mine is a pacific coast chopper. I made the mount just like the one you buy only I made mine to fit the engine exactly with out the up right tubes. I am not sure why it sheared the bolts other than they were the china bolts. I tapped the holes to 1/4 inch and use grade 8 bolts. Hope this solves the problem. To tired after work and refitting the motor to go for a ride. Tomorrow sounds good. Thanks for the advise and I will share my experiences.

 

[Big Red]

oh yeah. this is true. important to get the rear mount as square to tube as possible, and shim or file away any gap on the front. at least it works better that way for me. i guess you could file the rear just as easily get max contact between engine and frame.

then theres always a bottle rack lug or a derailleur clamp in the way, that needs weasling around!

Filing on a mount is not the answer. Any angle on the mount translates to an angle on the studs. If ya can't get a motor to line up on both mounts, Then it's better to set the rear mount right and make or buy a front U-bolt mount kit and BEND IT to fit the frame. Only because no one really makes an inexpensive REAR mount kit. Manic Machanic makes them. They make GREAT mounts, Font and Rear, For a GREAT price. Or even best yet, Weld in your own mounts if ya can.
Big Red.