86 250SX Situation

[patriot1]

Another day-Another puzzle


So, I took this good looking girl for a ride yesterday and when I got off to take this picture of her:

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she died and I couldn't get her to start back up so I pulled her to the shop.

I sprayed starter fluid to check for fire and not even a pop. I then started where I should've to begin with and verified fuel. I then looked for fire and had a fat blue spark.

I then read my manual checked the compression...

35lbs

Almost no compression!! What happened?

The oil was fresh and full.

It did not smoke at all.

I checked the oil today but it didn't seem bad but I am not sure.

I have not checked the valves.

Thoughts? Advice? Prayers?

[ATC King]

I'd like to suggest something, but these things have decades of unknown history and with so many oddball failures, I'd just be spitting into the wind and getting back someone else's spit.

Pretty much, refer to the repair manual flow chart, smoke it, and start taking things apart.

[patriot1]

Thanks King, as always, I appreciate it. I read the manual and thats what made me check the compression. However, my clymer manual has not said anything about "low compression" and what to look for in this situation. (At least that i have found in there yet-but I am still looking)

I've also searched the web as well as 3WW threads and have came up with a few ideas but just ideas.

My next thought was to check the valves and drain the oil and see what is in it-if anything, as soon as I get the chance.

I was just hoping someone might have some insight and had experienced this before?

[BarnBoy]

Head gasket? Carbon between the valve and seat?? Timing chain snapped and bent a valve?? That sucks man, just take it step by step but that motor will likely be coming out either way.

[shortline10]

May have just sucked in some trash threw the intake , what condition is your air filter in ?
First thing is to definitely check your valve clearance , if ok then put some motor oil in the cylinder to see if the compression jumps up . If no change in compression then it’s time to pull the topend .

[El Camexican]

Does that trike use a pull start? If so it should have felt very different when you went to pull it with only 35 #.

No chance it has a decomp setup that could be stuck/frozen open?

[ATC King]

At the end of the day, it'd be just as sensible to take all the suggestions, written on paper, placed into a cup, and drawing one.

Most things that get mentioned will simply be in the repair manual. It just a matter of starting at point A and working to B.

Are you sure it has good spark? Under compression, a spark is much different then in the open air. That's why inline spark testers work better than just looking at the spark handing out in the open.

Valve adjusters have been known to come loose or be stripped. Decades of monkey wrenchers will have that effect.

Jumped timing? Broken cam chain? If air can't move in or out, compression is going to be low.

In either case, popping the valve adjustment covers and watching everything while spinning it over by hand will tell you a lot.


Crazy end of the spectrum? Does the SX have a double wall head pipe like other ATCs? It's been know to happen, that the inside layer rusts, then collapses, blocking the exhaust. Either in the header itself, or chunks make it to the muffler. Low compression would be a symptom there too; no air out = low compression.


You may be hoping for someone to just know, but it's simply going to come down to you digging into it, giving feedback/pictures, and moving on to the next suspect. You've clearly got some understanding about these things, but there have been many times that newbs post questions like this and the issue is never rectified in the thread. The owner just doesn't have the decency to put in the work to solve it and let everyone know how it turned out, because they probably just came here hoping for an easy fix, so they could flip it, with the aid of decades of experience they didn't have to contribute to.

Not that it's what you're doing. You've been bringing to good trikes back and seem to be genuinely interested in them. That's just me putting out there how I've seen it play out a lot of times and possibly why many of these threads don't get the activity they once did.


"I was just hoping someone might have some insight and had experienced this before?"

I think most of us have had something just poop out during a ride, and not be very clear as to what. Sometimes it's completely unrelated to what we think, we get tunnel vision, and make it more difficult than what it is. There's also those oddball occurrences that only happen once, and the stars never align like that again. Kind of like pulling a float bowl, and seeing the main jet just laying in the bottom. That one is not in any manual.

[patriot1]

lol! I totally understand everything you just said King! I totally get it! This was my "good one", my go to rider.

El Camexican: It does not have pull recoil but very easy to kick.

So to update:

I didn't have much time to spend on this today (and most of it was spent on getting the timing indicator cap off-got to be a better way); however, I did get the valve covers off and the engine set to TDC and both valves had zero play. I could not move either of them and the feeler gauge of course didn't fit.

I had to stop there and take care of work that pays the bills.

Shortline: You never know when someone will post something that makes sense. When you asked me about the air filter-I remembered that I didn't put one on because when I finally got the Maier fenders on (which was a challenge) I didn't want to take them back off. ding ding ding!!

I'll keep you posted.

Thanks to all

[Jim mac]

if there's no valve clearance I'd just back the adjusters a little and see if you get your compression back. I bought a atc70 back in the day not running, backed the adjuster and it was running in 10 min. jim

[MrConcdid]

Check the valves, set them loose.
Re run the compression test. Make sure choke is off and throttle is open. If still 35 spray some oil in cylinder and re run compression. Re torque head bolts, look for a loose one. Re check compression. If still 35psi. My guess would be a collapsed ring or bent valve. I had a valve seat crack and a piece came out, but that gave a reading of zero compression.
So having some makes me think everything is in place but just not sealing.
After all this if no improvement pull engine and do a top end and valve job.

[patriot1]

Loosened the valves and got 90 psi on compression test

oil in cylinder and got it to start and run and idled well-rechecked compression-90 psi

Set the valves and installed air filter, let it run for awhile and rechecked compression-90 psi

no smoke, runs great

I'll look at the top end rebuild when I get done with the 200 (no letter)

[cals200x]

Do these have a compression release? If so could it activate on its own? Or partially?

[MrConcdid]

Loosened the valves and got 90 psi on compression test

oil in cylinder and got it to start and run and idled well-rechecked compression-90 psi

Set the valves and installed air filter, let it run for awhile and rechecked compression-90 psi

no smoke, runs great

I'll look at the top end rebuild when I get done with the 200 (no letter)

Most of my carb issues are really valve issues!

[patriot1]

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I ended up deciding to replace the top end or at least tear it down and see what the problem was. However, I need advice on getting the exhaust apart. Anyone...Anyone???Bueller???

Thanks guys!

[shortline10]

Lube , heat wiggle wiggle repeat lol .