I have an os46 fx engine. There are a total of 4 screws to connect the back plate to the engine body. Problem is that One screw does not tighten because the threadness on the hole(the one in engine body) is gone. I know I can buy spare screws and back plate but problem is in engine body. Is it ok to run the engine with only 3 screws on? if not anyway I can fix it?

It's better if you repair it, or you can maybe try try to get some liquid metal paste and put that in the hole, then put the screw in. when it's dry you can unscrew the screw and put the backplate on again. don't know if this works, but you can always try.

does the screw got any grip in there? or is it so loose it falls out?
when it's got any grip at all, you can try tapping new threads in the screwhole.

Can you tap it to the closest american size?

What you mean by tapping it to closest american size? I am sorry im a little dumb here.

Faisalk,

A tap is a tool used to create an internal thread in a hole, so a bolt turned into that hole will engage and hold.

What you were told is to get a larger tap - not too big for the housing, to clean out the remains of the old threads and to make a new, clean, one-size-larger thread.

When going to a hardware store, or a metal machining factory, you should take the engine crankcase and the old backplate bolt.
It is advisable to use a tap with a larger diameter, but the same pitch. I.e. if the bolt is 3mm-x0.5, tap the hole 4mm-x0.5.

You will need to use the correct bolt in that hole, not the original piece.

An alternative, cheaper fix is to use JB-Weld in the hole.
If the bolt is not tightened to strongly, it could hold.

In the future, be careful not to cross-thread the bolt and not to overtighten it.

Sincerely,

hMMMM. Can I run the engine with only 3 screws on? It seems to be running fine uptil now.

Faisalk,

If the engine manufacturer though 3 bolts at 3 of the 4 corners are enough, he would not have added the fourth...

The bolt also holds the integrity of the crankcase...

For a short time it may run OK, but I would advise against it.
Fix it as soon as possible.

I have two ways I have repaired engines with this problem. The first is just get a longer screw, you can measure the depth of the hole to see what you need , just be care full & don't over tighten . The other I have used is to find a much longer bolt with a nut on it , screw the bolt in until it bottoms out then tighten the nut down on your back cover, cut off the excess bolt. The manufactures have more threads in hole than they have bolt length, these have worked every time for me . Good luck MAX H.

So long as there are no leaks then you should be fine with just 3 screws. Be aware though that any screw hole that goes into the crankcase MUST be sealed.

I have my doubts that the backplate adds much integrity to the crankcase when you consider the engines that use a plastic backplate (I think even Irvine uses them).

Following your threads I'm glad not to be one of your engines, QUIT FIDDLING AROUND WITH THEM AND GET HELP FROM EXPERIENCED PEOPLE!!!!!!!

Maybe not the brightest candle on the cake, but give the man a break! Look where he hails from. He is NOT going to find a club full of friendly helpful flyers around the corner from the bazzare anywhere in Pakistan. He's doing the best he can with the resources he has, which by-in-large, means this forum.

Elmo Te

You are right to a point about giving a break. I do feel that the poor guy needs help and some of that is advice on how not to destroy good equipment. Given time he will no doubt know a lot about engines from all of his experiences both good or bad.

He was advised of a local club in April:

His help may be 20 miles away & that may be a long way on a bicycle. He's just learning the hard way , hope he & the engines survive!
MAX H.

Guys its not that bad out here. You guys still think that we drive on bicycles and theres no electricity seriously I was in Usa for 3 years for studies and half of the Americans didnt know where Pakistan is and half of them thought that Pakistan doesnt even have electricity Well its not that bad out here. Agreed we are far behind than USA but we do have cars,electricity,Mcdonalds,Pizza Hut etc. A Mercedes S class here costs around $150000(lot of duties) and there are more here than ive ever seen in my 3 yrs in boston(trust me)

FaisalK,

If the hole is just stripped, you can likely use a slightly-longer bolt of the same diameter. There shoule be good threads slightly deeper. The O.S. Max .46 FX uses M3x8 screws for the rear cover. A longer 3mm screw would work, as long as it does not hit the bottom of the bolt hole. Just carefully tighten it and you'll be fine.

FaisalK:

Im still driving my 3rd Generation Burro, with Mag horseshoes with 3D thread, running on a 3.2Liter powered by water and extremly long green grass. It only gives me 2 kilometers a gallon but it is the best around here.(Mexico). OOOOOppppsss, forgot tu mention my exclusive FOX boots, which enhances the feel of the road.
Viva Mexico!!!!!!!!!!!!!!!!!!!!!!!!!!!

Quote
Maybe not the brightest candle on the cake, but give the man a break! Look where
he hails from. He is NOT going to find a club full of friendly helpful flyers around the
corner from the bazzare anywhere in Pakistan
Unquote

Elmot & FaisalK

Perhaps you have not seen one of my previous post that I repeat here:

"FaisalK
For your information there is an aeromodelling club in Karachi called M.A.S.K. and many
experienced modellers regularly fly glow, gas and jet planes on Sundays near Korangi
Creek Base. Some of them have held National and International titles. Instructors are
available and flying competency certificates are also issued on behalf of BMFA, U.K. by
their resident examiner.

If you need further info or help for your engine please contact Zahid at 5851646."