Trailfire Knocking

[guitardude081]

Before my 1980 340 TF gave up the ghost this past Saturday, it was making a very mechanical knocking or wrapping noise. I haven't ridden this sled myself in 5 or 6 years. It made the noise back then as I recall. I've always assumed it was from a weak clutch spring making the primary engage and disengage rapidly. My Grandpa recently passed away, and this sled was given to me along with my Spitfire. I haven't gotten a chance to tear into the engine yet, but when this wrapping sound came about on Saturday, I knew right then and there that it was the familiar knocking sound of an engine teetering on the brink. I guess what I want to know is besides pistons and heads, what kind of parts will I be looking for. It's got good compression so I'm assuming that there's no real cylinder damage, but I'm sure the crank and bearings took a pounding. The culprit was most likely a faulty PTO crank seal and the resulting rust in the crankcase from years of neclect and sitting in high moisture areas. Looking in with the bore scope, the cylinder walls are ok, but there is little to no piston wash on the PTO piston which is normal with a lean condition. I won't get to this now until this spring, but I can get a used 340 or 440 motor for $50. My motor needs a lighting coil as well. I'd like to save the original 340, but Before I tear into it, I would like to know what I will most likely be dealing with. Buying a junk yard motor for $50 is a always a gamble. With the original 340 at least I have a good idea of what I need, with the Junkyard motor there may be hidden suprises. I'm just curious as to what components were probably damaged to the point of needing to be replaced.
~Jack

[JDT]

I would first make sure that it is in fact the engine that is/was making the noise.

Look at the drivers and note the condition of the cogs.
And while you are there grab the drive shaft and try and move it side to side and up and down. You have a bad bearing on the shaft.
Check the chain tensioners in the drop case. You may be hearing the chain jumping on the sprokets.
And the clutches you mentioned should be inspected closely.

Check the track tension as the noise may be do to a loose track that is ratcheting on the drive sprockets.
Make sure the motor is not loose on the mounting plate and that the motor mounts are all good.
A broken track cleat may be the source of the noise.

Check the jackshaft bearings and allso the brack disc. If the key is missing on the disc that will make a lot of noise.

Lots of things to look at before you blame the engine.
And the only way to tell what you will need for a engine repair is to tear it down first assuming it is an internal problem.

Todd

[JDT]

It was like I was prodicting my own future....

Today I started working on yet another JDX. I was inspecting the undercarriage and grabed the drive shaft and tried to wiggle it. It did.




So now I will be replacing both bearings tomorrow.

Todd

[guitardude081]

Most of the noise was before clutch engagement. It was the engine for sure. Once the knocking was severe enough, the engine would not rev above 1000 rpms. It would idle there, but it would complain when you gave it throttle. I shut it off before I completly destroyed it. My main thought is that it may not have head gaskets. The place we normally have our sleds serviced at has a tendancy to reassemble engines without gaskets. We found this to be the case with the Spitfire. "They probably burned so bad the got sucked into the motor" is the usual response. I've got 2 new pistons on the shelf. Being that I won't get to it until this spring, I dont want to tear into a junkyard motor only to find a rusty crank and pitted heads. I'd like to have everything ready to go when I tear the sled down. I was just curious about what parts I should be searching for. Good call on the drivetrain stuff though. That was my first thought when it was acting up on the stand. I'm planning a restoration this summer, so all of that stuff will be reconditioned or replaced. This sled has gone through 16 grandchildren in our family, and Being the second oldest, I've definatley given it it's fair share of beatings. After all the abuse my Dad, Uncles and us kids gave it, it finally said uncle.
~Jack

[Mr. Deere]

Why keep going back to a place that doesn't install gaskets. BOB

[guitardude081]

We haven't gone to them since we found the problem with the Spitfire. The missing gaskets in the TF is just my theory. I remember that my dad brought the sled in when I was 10 or 11 to have the head and base gaskets replaced. It hasn't been used much in the last 10 years, so a problem like this is not really out of the ordinary. Preigntion/detonation is the sound I was hearing, and it was probably caused by the PTO crank seal. Missing (or possibly cork) gaskets would mean a bad seal around the head area which would also be another place for air to get into the engine causing it to run lean. I'm just trying to put together a parts list without tearing into the engine. Having an 80 hour work week limits the time I have to work on my sleds. Finishing my 83 Sprintfire restoration is my priority as far as sleds go.
~Jack

[qwerty]

the condition of the engine is pretty hard to predict, unless you have a crystal ball.
if you need confirmation as to wether or not to buy the parts motor i would say for $50 yes. its worth the gamble.

[JDT]

I agree with Qwerty.
Surely there will be some good parts on the engine. And maybe the thing is actually very good.
It maybe cheaper to fix the junkyard engine that the one you have in the sled now.
But you will not know untill you tear down either one.
As far as stockpiling parts start with a complete gasket kit(with crank seals). Pistons maybe.
Let us know what you find after you get your hands dirty.
Todd

[Danzig]

I will place a bet and say its the needle bearings on the wrist pins and you have connecting rod slap on the pin the needle bearings ride on...