TRailfire 340 problems

[tmartin]

I recently acquired a 80 trailfire 340 and rebuilt the engine and went through the carb and chassis. i have been running it and it seems ok. i took it out yesterday in the warm and the noise i have been noticing got worse. I ll try to descibe it for you. It used to be that it would only do it when the machine was cold but now it seems to be getting worse. The machine seems to idle fine,not missing or anything, when i engage the clutch it seems to loose power and as i push the throttle it starts kind of hammering and then just takes of and runs like a champ. Its got like a lag at 1/4 throttle and like i said it hammers. Its in the motor and not the clutch. Have any of you experienced this and if so how did you remedy it. Its definately carb or ignition unless the crank is twisted which i do not think it is because i had it worked on. thanks

[guitardude081]

Did you have your crank checked? I had the exact same problem with my Trailfire. It turned out that it was a combination of a bad needle/seat and bad crank bearing o-rings. The sled would start on the first or second pull most of the time. It would idle fine and take throttle for the first 30 seconds to a minute then it would start knocking and bogging. It was bad enough to make it start backfiring...out of a bad PTO crank seal. Once it was up to speed, it cleared out and ran fine as long as I was on the throttle. What was happening was the needle and seat was just bad enough to fill the crank case about half way up the counterweights. It would try to hydraulic when all of the raw fuel was forced up through the transfer ports. When I tore down the engine I dumped out about 2 1/2 cups of raw fuel. Keep in mind that I actually drove this sled off of the trailer and into the shop before I tore it down. The crank was a few degrees out because of the hydraulic issue.

If your crank is out of phase, you could either be advanced and pre-igniting, or retarded and firing spark well after TDC and not igniting the fuel charge properly. I'd pull the plugs and the pulse line and crank the motor over to see if you have excess fuel coming out.

Other things to check for would be bad crank bearings, bad lower rod bearings, if you reused the upper rod bearings, those could be bad. Did you double check that you installed all 4 circ-clips on the pistons? Usually a missing circ clip will cause a seizure within a few seconds to a minute. I'd pull off a head and make sure that you're not getting piston to head contact.

These are a few ideas that I have without hearing it run.
~Jack

[tmartin]

Thanks i had new outer bearings put on the crank. Rod and needle bearing were fine. i put new o rings on the cranks as well as crank seals. I have 80 miles on this thing and i really noticed this noise in the warmer weather. i will check twist on the crank but i dont think thats it. I was wondering if a coill or box could do this.

[guitardude081]

A coil or CDI most likely won't do it but, if your stator is timed too far advanced it could be causing pre-ignition/detonation. Were the pistons and rings replaced. your sound could be piston slap as well if the rings are excessively worn.

The other issue I had with mine was that the roller spacers were gone, the rollers were stuck and the weights were almost oblonged enough to break through. The pins were so worn that they were starting to bend. This made for a heck of an engagement....it was almost if this sled had notched weights.
~Jack

[tmartin]

I did find the case half full of fuel. I rebuilt the carb this week with new rubber tipped needle and seat and new jets. I pulled engine completely apart and found what i didnt want to. There was a bunch of aluminum around the center seal. The crank must be bent or twisted and the bearings are carving into the case. It seems the worst on the stacked bearings on the pto side. The case is probably shot and the crank may be to. This was like this before my fist assembly of it but the crank looked good and turned over without a snag so i ran it. When i took it apart i found the pto side seal was chewed up already so there is definately somthing happening in that bottom end but the naked eye cant see it. I know a crank guy that might be able to enlighten me. Would that case still be usable with wear on the bearing surfaces or no? Thanks again.

[JDT]

I would suggest finding a different case.

[guitardude081]

I would send the crank to Jerome. It may have been bent or twisted. It could have been assembled without the spring pin on the crank in the hole in the case. The case doesn't fit together too well like that but with enough tension on the bolts it may go together. I'd get the crank fixed and get a different case. The 340 and 440 cases and cranks are interchangeable.
~Jack

[JDFanPa]

if neede i can set you up with a bottom end to use I got a few extras

[tmartin]

Thanks for the offer on the bottom end but i have a few leads locally so i will check them out first. If i run into a wall i may take you up on that offer. Do you have a price in mind? I now know i will need a new case and still am not sure if the crank will be salvageable. I guess it never hurts to have a spare. Thanks

[JDFanPa]

Not much maybe $20 bucks and shipping it would still need new seals but should be no probs with the crank or the cases. You can email me at jesse_jameswannabe@yahoo.com if intrested. I could send you pics or what not if you like.