1991 suzuki lt4wd rebuild time?

[Joeguy]

I been working on this thing for like 2 months now and it will not run right, is very smokey, and has a pretty loud tap that i think is in the bottom end. Not sure how much the parts are but i will put the time into it if they are pretty cheap. Im not very experienced but going off how the plug looks and the oil on top of the piston i am getting a whole lot of oil coming in from somewhere, not sure if it can come from the valves or if the rings are just shot, my cheap scope cant really see the walls of the cylinder too well.

[Gwbarm]

I think you are correct does look like worn rings. Good luck with the rebuild.

[Joeguy]

Thanks, gona have to figure out how it all comes apart with the rear end being like part of the engine. Looks kinda simple atleast.

[Gwbarm]

Oh, I missed that, you got to go into the bottom end, that could end up being a big job and get expensive if the crank is bad.

[Joeguy]

Ya if the crank is bad im just going to junk it sadly. Hopefully an easy fix.

[Gwbarm]

Good luck! I will be curious to see what you find.

[Sandro]

So how did you go? Just joined and saw the post. What did you end up doing and how did it go?

[Joeguy]

Honestly i started to work on another quad and got it running pretty easily so now im kinda wondering if i even want to put the money and time into this one. Might keep it around as a project for later but i dont got a whole lot of free room. I did however fix my big hole in the fender with a plastic welder, i only have staples in it now but it looks alot better than zip ties.

[Joeguy]

Well got bored today and tore into this thing finally. Bad news, we got damage. Also, ya it at least needs a bearing in the bottom end. What a nightmare to get this thing apart, i do not enjoy working on this thing at all. I am not excited at the though that now i would need to pull the engine to fix it so i think it might just be junk time. You guys think its worth the time and money at this point? It seems pretty beat to me.

[Mech]

Didn't see the vid of the bottom end. Slow internet so I'll try again later.

Getting the engine out isn't so bad. Once the body work's off you take out the left rear suspension and wheel and all in one piece, then undo a frame member and gear shift, and the engine slides out to the left. Getting it back in you have to line up the right rear drive shaft but that's simple.

That rod, if it moves four mills it's probably ok, but six mm would be too much . Six mm is 1/4".

The most play, and any roughness, will be when the crank's about twenty degrees past top dead center.. If you tip the rod back it will be about right. If you check for endwards movement of the rod there, you shouldn't feel any..haha. It shouldn't rock more than about 4mm, and if you push and rock the rod on it's bearing it should feel smooth..

Cranks aren't too hard to do if you have a workshop with a press or good pullers. My sons used to do their own cranks when they were twelve and fourteen.. maybe even earlier. They did lots and they never had any problems. I've done lots. I've never had a problem.

If I was doubtful about it's being worth doing, I'd probably fit a top end/fix it, and have a listen to how it sounds, then pull it out and apart if I had to. Just saying.. It's old as you say.

The manual will tell you how much rod movement they think there should be. My 4mm is just a rough figure.

[Joeguy]

Wish a top end rebuild kit wasn't like a hundred bucks. Im going to do so actual testing and measure on that rod and see how its looking because honestly it feels smooth and doesnt have much play if i like pull in and out its just side to side. Never done much engine work except like weedwacker and tractors so im gettin a bit more involved here.

[Joeguy]

Also anyone know why the 2nd ring and the piston were like shattered into pieces?

[Mech]

When engines get high mileage the rings wear the grooves, then the rings start to flip and flop as the piston goes up then down again, they act like they were a disk getting flexed concave then convex.. that breaks them and then the ring groove breaks too.

Rings also break if the ignition timing gets too advanced till there is "pinking".

You need to test the rod bearing at the place the wear takes place, which is about twenty degrees after tdc. You just have to carefully work your way over that area checking for play or roughness in any spot about that angle.

[Joeguy]

Ah damn i only tested at tdc, its like .100 side to side at that point if that matters ha. Ill have to check again properly tommorow. I did hone out the cylinder a bit today and it seems like it cleaned up well except for right at the top there is a bit of an indent, ill have to get my bore gauges and check and see how much it actually is aswell as the rest of it.

Edited November 25, 2024 by Joeguy

[Mech]

The side play/rocking will be the same on the worn spot because the worn spot is just a narrowish band across the crank pin. If you are pushing down hard though as you rock the rod over the wear you feel it, and there might be the tiniest amount of endwards movement there, but mostly not, not if the side play is within limits.

Side play/rocking of 0.1" sounds ok. Good even. I've put bikes together with more side play than that.

That lip at the top is a measure of how much taper there is in the bore. Too much taper shortens the life of the rings, but a certain amount is ok. The thing about reusing a tapered bore(if it's within reason), is that when you put a new piston in, with new rings, the top of the new ring is going to hit that lip and break the rings within no time. To use a bore with taper you have to remove that lip, and if you think you'll be all fancy about it and use a "ridge remover', it's going to not work. The taper is worse in line with the rod swing, and if you use a ridge remover till all the lip's gone at the worse place, then you are going to have under cut the bore at the sides. What you have to do to do a good job, is use a triangular file ground on it's end so it's a three sided scraper with slightly curved cutting edges. Then you just gently cut/scrape metal away from there it's needed and no where else. It's easy to see what's scraping and when the two surfaces are flush.

[Joeguy]

Ok well i checked the bore over and got a roundness of like .0015 and a taper of .003. That ring does not seem to be a ridge its more of an undercut and it seems to be like .002 deep but im only checking with some cheap bore gauges so its kinda hard to tell exactly. The bore was at 2.601 inches and the piston was 2.586 inches. So would you recommend that i try to clean that ring up a bit with my hone or would it be ok as is.

[Gwbarm]

I am as cheap as they come, i have done what you are doing many times it works ok for my application i restore old 60s motorcycles that probably dont get 100 miles put on them in a year, but if i was doing what you are doing for a good running ATV that gets ridden like an ATV, very hard, i would go ahead and get a rebore since you are going to have to get new piston and rings anyway. You can make what you have usable but you will never get it exactly back round without a rebore.

[Joeguy]

Hmm i guess ill price out a local shop then, to bad i quit my other job that had a Sunnen or id just do it myself. This was a really cheap purchase and the quad is kinda beat up so im not too keen on spending a bunch when i could just sell the parts off this one and put that money + repair/parts bill and get one that already runs. Been a fun experience so far atleast, and learning.

[Mech]

The 0.003" taper means the lip at the top will be 0.003" also. That will break a new ring.

I don't think your measurements are quite accurate though because the standard bore should be bigger than your worn measurement. If your measures are right, then it seems that the piston to bore clearance is right at the wear limit(though we can exceed that and still get a reliable engine), but if the standard bore is slightly bigger as the book says, then there is a bit more piston clearance than they recommend for a guaranteed good engine. I could get that running though, and not needing any oil between services probably

If it was me, for myself or for a customer, if they were agreeable, check the crank, I'd take the ridge off, check the piston to ring clearance, then fit a set of rings with a barrel base gasket, head gasket, and valve grind and seals. It would go for years, but only because I'd take care to minimise the ring gap and bed it in carefully. If the piston was worn and needed to be replaced, I'd bore it.

An engine with taper makes the rings work harder to maintain a seal, they have to expand and contract every stroke, so if they get overheated, or don't bed in, then they'll let oil past.. If the rings are bedded in carefully in the first ten minutes after first start, and don't ever get overheated, then it'll be a perfectly good engine. We can generally wear our two pistons before we need to do the crank.. 

It's like Gw says, you could get it to go again, but it's not going to last as long as a rebore, especially if the work and care riding aren't all they should be.

[Joeguy]

I measured with just some cheap bore gauges and my digital calipers so its not the best measurements probably. Ill see if my buddy that does ID work can bring me better stuff to check.

[Mech]

The difference between your measure and the standard bore was minimal, you might have measured on a bit of varnish or carbon build up.

[Joeguy]

Man now i just noticed i need a camshaft ha, just keeps on adding on. Some how did not notice this till today when i was wiping everything down.

[Mech]

Yeah that's a bit chewed. Is that surface hardening lifting, or where some bit of steel has got in there ? What does the rocker look like ?

[Joeguy]

Doesn't appear to be lifting i think some chunks got in there. Rocker has a small mark on it, i think i can feel a small something there but nothing i can like catch a fingernail on or anything.

[Mech]

And metal in the filter or sieve ?

[Joeguy]

Well i changed the filter when i first got it and i did not see anything but i guess ill have to drain it and check it all again. Do you know where the sieve is at on this? If not ill take a peek through the manual.

Edited November 30, 2024 by Joeguy

[Joeguy]

Also dumb question but how much space should there be between the piston and the walls of the cylinder? Like if i buy an oversize piston should i get it bored out to like maybe 5 thou larger than the piston? Im just not sure how tight of a fit it is supposed to be.

[Mech]

I'd got confused between this and another online engine job that's going on. I'd forgotten about the broken rings. Slapping new rings in is not a viable option.

Since you need a new piston, then it would be worth boring the cylinder. You'd have to see what the new piston's availiable in. They will come either 0.010" oversize or 0.020" oversize. The clearance will be set by the guys doing the boring and it should be to the book. You could fit a new piston and rings in the worn bore, and the engine would(assuming the crank is ok), be good for years. A car like that I'd patch up for a customer and guarantee it to be reliable, using no oil to start with, and perhaps after the four years it may need a top up between services..

If I was doing a rebore and new piston though, then I'd have to be confident the bike crank was going to be up to it, and the gearbox etc, so I'd strip it entirely and clean it and then do the engine work if it was going to be a good unit. I wouldn't buy anything or make any decisions though till I'd stripped, cleaned, inspected and priced everything..

 

Edited November 30, 2024 by Mech

[Joeguy]

Im just going to gamble on the bottom end because im lazy and it feels ok i believe, might be a waste of money but oh well. I didn't notice that the rebuild kits say what the bore should be till i just looked so ill get that done, luckily my buddy can get it done cheap for me. Hopefully be getting it back together after that, and we shall see if my cheaping out is going to work ha.

[Gwbarm]

I would have the piston and rings in hand and take it with the cylinder to the machinist as a guide for the rebore. Depending on how bad the cylinder is you might have to upsize 2 sizes to get it right the machinist could tell you this before you order the kit.