Small engine repair anyone????

[vrodjason]

I hope someone on here can give me a little insight into my problem. Okay this is what I have: 1978 Sears (not Craftsman) GT18 Garden Tractor with an 18 hp twin cyl. Onan. Here is the problem: the front cyl. is dead. What I have done so far: Checked coil-good, took off dual outlet coil replace with single outlet, ran to front plug- still dead. So I think I have eliminated the coil totally. I think that the problem is internal, maybe the cam? Any ideas?

Jason

[Juneaudave]

I'm not an expert on these by any means, but I think you need to do a little more diagnostic work. I think my next step would be a compression check.

[vrodjason]

Yeah that was going to be my next step. I was hoping it wasn't internal b/c I didn' want to pull it apart!

[madjack]

vrod, it takes 3 things to make it go bang...spark/fuel/compression...if you have spark and you have fuel then all that is left is compression...check compression and see what's what...if no compression you will have to take it apart to see what is wrong...probably a valve problem which could be caused by the cam but may well be a broken valve or something else not nice..............
madjack

[vrodjason]

madjack, I know for sure i have fuel and spark. I was thinking along the same lines as you- cam wiped a lobe/ valve not working right. Thanks for the help.


To give a little back groung on the tractor. Its a 1978 Sear GT18 with the Onan, 3 speed trans with hi and low giving a total of 6 for. and 2 rev. speeds. I have the turning plow, disc, snow/dirt blade, and a 46" mower deck. It aslo has loaded tractor tires with wheel weights and a set of chains. I bought it off of a good friend of my dads who bought it new in '78.

[Mike_La]

Could be something as simple as a stuck valve, if you're lucky.

Before disassembly, check compression(record it). Add a thimble full of oil to the cylinder, wait one minute, re-check compression. If compression does not rise significantly, it's most likely a valve problem.

To do a visual check, the head on that engine is fairly easy to remove.

Have you had this tractor for a while, or recently acquired it? (History)


Mike

[vrodjason]

I just bought it back in mid summer. I bought it from the original owner who is a family friend and has had no problems like this before.

I'll have to drag it back up to the garage this weekend. I've been busy on my house remodel and set the mower aside till I got done. With winter on its way I'd like to get it fixed so I can push some snow with it! yah! not really yah. more like oh no.

[emiller]

Check for spark at the spark plug, here are some types of spark checkers,
http://www.toolfetch.com/spark-testers.shtml if spark do a leak down test.
http://www.carcraft.com/techarticles/11 ... index.html Your local auto parts store should have a lend a tool program. Make sure you get instructions to what ever tool you use.

[Kevin A]

I hope someone on here can give me a little insight into my problem. Okay this is what I have: 1978 Sears (not Craftsman) GT18 Garden Tractor with an 18 hp twin cyl. Onan. Here is the problem: the front cyl. is dead. What I have done so far: Checked coil-good, took off dual outlet coil replace with single outlet, ran to front plug- still dead. So I think I have eliminated the coil totally. I think that the problem is internal, maybe the cam? Any ideas?

Jason

Does the other cylinder run or even try to fire? If it does, I'd do as others have suggested and check compression in the dead cylinder. Another thing you can do if the compression is low, bring the dead cylinder to TDC (top dead center) on the compression stroke and apply compressed air to the cylinder and see where the compression loss is going. ie, out the exhaust, through the intake or into the crankcase. It has to be going to one of the three. This will give you a pretty good idea where the problem is. If neither cylinder wants to run i'd be looking at carburetion or ignition problems as the culprit.

[vrodjason]

I' m going to test the compression tomorrow and see what happens. Kevin A. thanks for the advise on put the air too it to see where it goes. I don't think it is an ign. problem but could be a carb or intake problem. Could a leaking intake gasket cause this? A guy at work said these Onans are bad for this. I'll let ya'll know something tomorrow.

[Kevin A]

I' m going to test the compression tomorrow and see what happens. Kevin A. thanks for the advise on put the air too it to see where it goes. I don't think it is an ign. problem but could be a carb or intake problem. Could a leaking intake gasket cause this? A guy at work said these Onans are bad for this. I'll let ya'll know something tomorrow.

Does the other cylinder run?

[vrodjason]

Yeah but not well. Let me tell you how this all went down, it didn't just happen. First it started acting like the points were going bad. So I filed them a bit and adjusted them. While I was doing this I also adjusted the plug gap. The motor ran a little better but still had a slight miss. Was mowing one day and the tractor just died. I thought it was the coil going bad. This could cause a miss and cause a motor to just die when total failure occurs. Between me and my dad we had two Ford coils. I wired them up- one for the front cyl and one for the rear cyl. The rear cyl will run but not like it did- fair at best. Sooo, what do you think?

[Kevin A]

After you check the compression I would replace the points, condenser and spark plugs. I could be wrong but I believe there is a fiber plunger that opens the points on the Onans, if that is worn, replace it too.
If you still have the original coil pack, reinstall it and check to make sure you're getting spark.

[vrodjason]

I have replaced the points and plugs. The only thing I haven't replaced is the condenser. We'll see what happens tomorrow. Thanks for all of the help so far!!!!!

[Kevin A]

Keep us posted, we'll get it running.