I need some help.

I have a mac 28cc engine with a CH ignition on it. I flew it on an ultra stick about a month ago.

During the flight, it died after a couple of minutes and I knocked the gear off on the deadstick. (I didnt make it back to the landing strip due to balance probs. That was addressed in another thread)

Anyway, now it wont start. Got fuel, got spark, battery is charged. I was running a MA 18x8 on it (overpropped, i know) and I havent touched anything since. I even pulled the plug and squirted some fuel into the cylinder. Also tried Hot Shot (I avoid that stuff if at all possible). Not even a pop. My arm is very tired.

Before this, once primed, it would kick on the first or second flip.

I dont know what could have happened. The engine didnt hit the ground and when I pull the plug it seems to have a good spark.

Any suggestions?

In my frustration, I am considering putting my Ryobi 31 on there and just deal with the magneto and starter.

Rob

A long shot...Maybe the hub slipped on the crank and retimed it....

Hmm.

Never checked that. I do know that the sensor mounting ring is still tight, but I would not have any idea as to how to check the timing now.

Is the hub a press fit or is it keyed?

There is a black line drawn on the hub itself. Perhaps that should line up at 12 o clock at tdc.

I'll check that one night this week.

Thanks.

There should be amark on the timing ring and a mark on the hub. They line up at TDC. Nothing to do with clock positions.

Macs are bad about the crank pin coming out of the counter weight where by it rubs a hole in the back plate. The engine will never do anymore than pop after that.

Enjoy,

Jim

crank and ignition lines line up at tdc. I will check the backplate as w8ye suggests.

I have pulled the motor off and see nothing cosmetically. I will have to tear it down and check it out. I have 2 other macs that I can use the ignition on, but I think I will try the Ryobi.

What would I need to get to put the ignition on the Ryobi? Just another hub with the magnet or will the mac hub fit on the ryobi?

Ok, more info.

I pulled the backplate off and I found what appears to be a "staple" bent up with the ends curled like an S. I think it probably used to be some sort of retaining clip/ring/wire/etc.

Nothing else looked damaged but I have not pulled the cylinder off. I dont know how long that had been rattling around in there but I dont see any major problems.

Perhaps I will just put all of the ignition parts on the working mac given to me by my neighbor. I tend to spend more time trying to troubleshoot gremlins than I would have spent just swapping over to the other engine.

Any ideas what the problem could have been? I havent looked at the intake side of things, perhaps a leak somewhere?

Perhads part of a crankcase seal?????? If it does not seal on the bottom end it isn't going to run.
Ron

seal looked ok around the backplate. It is a rubber seal, pretty thick.

This definitely looks like some sort of spring steel type wire.

front engine seals. There are 2 of them.
Ron

Actually that has 2 sealed bearings. On the front of the crankshaft.
Ron

There are two sealed bearings on the front and then there is a rubber biscuit (also called a seal) in between the two bearings.

Enjoy,

Jim

Oh, well that could be.

All I found was the wire though. If it were leaking wouldn't there be more than the retaining clip in the case? I guess it could have just come loose though. Maybe it hasnt flown apart yet.

Dang. Bought that engine off e b a y. I guess I'll just throw the ignition on the other mac. That way I wont have to change any of the mounting holes, etc.

Thanks for the info.

Rob

C R A P !

My other Mac does not have the end of the shaft threaded for the prop nut.

Don't really feel like pulling the motor apart to swap cranks right now.

I tried to slip the hub on the Ryobi shaft, but it is a different size so I cant put the ignition on the ryobi without a new hub and maybe a new ignition sensor mount.

I guess nothing can be easy.

Guess I'll mount up the Ryobi with magneto. Just need to drill more holes in the firewall I guess.

Done venting. (for now)

Rob

Better taker the cylinder off and look at the piston..the curled up piece of wire sounds like a wrist pin clip...You DON'T want the pin to slide sideways in the piston...

that was my thought also

update. Looking through the exhaust port, the piston goes up and down (I knew it did) and the ring looks ok for the small section I can see through the port but....

when I put my thumb over the spark plug hole and turn it over there is very little pushing and sucking on my thumb but it does do some. Now for comparison, I went over to my Ryobi in the same condition and turned it over and there was much more pressure on my thumb. When using light pressure it would actually blow air past my thumb. The Mac would not do that with the same pressure.

So, there is not enough compression in the Mac. Piston/ring problem?

Can I just put that crank in the other Mac that I have? Is it a lot of trouble or difficult? Will I need any special tools like a press or anything? My other mac is not threaded for the prop nut.

Thanks.

Rob

The 28/32 Macs all have interchangable cylinders and pistions. So just swap the good combo on to the good lower end.
Sounds like a wrist pin clip to me too. Some Macs have two and some use a undersized ridge on one side with a clip on the other.