98 Bayou 220 low compression

[DZL1]

Question for you guys. I have a 98 bayou 220 that I picked up cheap cause it's wasn't running. So it's has very low compression. It is getting spark and fuel. 

What should my next course of action be? Any other tests I should perform or where to start looking?

Thanks in advance.

[Mech]

Check the valve clearance.. Check the cam timing.

Then check the compression with a gauge, then put about two teaspoons of oil down the spark-plug hole and check the compression again. If it comes up by more than about twenty pounds (depends on what the first figure was) then it's an indication the rings are leaking/weak, if the two figures are almost the same then it's probably a valve.

If it has more than a hundred pounds then it should run, just, but be hard to start.. Less than eighty and it's unlikely to start at all.

[DZL1]

So I checked timing and at TDC the cam sprocket dimple lines up with casting bump. I haven't checked valve clearance. I will check that tomorrow. I did check compression before anything and it was at 20. After checking valves I will do the oil down spark plug hole test and post results. 

 

Thanks. 

[Gwbarm]

That low i would suspect a stuck valve or at least one that is not closing all the way.

[Mech]

Yeah compression that low it will be a valve problem. If the/one valve has a lot of clearance it might be that valve sticking open..  Try tapping it and/or turning it ..

[DZL1]

Ok so check the valves and they were not adjusted properly. I then adjusted them to spec. I rechecked compression and it still was around 20 psi. I then poured oil down the cylinder rechecked compression and it went up to 48 psi.

going by what was said earlier in the thread, it indicates that I have leaking rings. A top and rebuild is what is needed? Or is there something else I should test?

[Mech]

At such low pressures it's almost certain that the rings and the valves are at fault here.

You say the valves were not to spec.. so were they too tight or too loose ?

And I suppose there's no sign or sound of the head gasket beingreally badly blown ? No whistling or whooshing (haha) sounds ?

[DZL1]

They where too tight. No gap. I'm going to perform a leak down test tomorrow and see if I hear or better yet what I hear and where. At this point It wouldn't surprise me what i find. 

Once I perform test I'll post results. Thanks for your help. 

[Mech]

Ok, too tight at least means the valve isn't bent.. haha.. or stuck open.  Probably burnt.

[DZL1]

I performed leak down and getting air from top breather. I'm also getting air from the lower part of the motor. Specifically the TDC sight hole and the  wire grommet above that and the surrounding area. Also the top long bolt hole of the recoil pull start cover. 

 

 

Edited January 18, 2025 by DZL1

[Mech]

Bad rings.. or badly blown cylinder head into the chain case.

[AnthonyT]

If you know someone with a borescope camera. Get some eyes on the cylinder walls. Will tell you right away what your problems are.

[DZL1]

Ok I will look at cylinder walls. 

@Mech, that's what I'm thinking as well. 

Will have a look and post my findings. 

 

Thanks again. 

[Mech]

When you are pulling the cylinder up, wrap a rag around the con-rod to stop broken ring falling into the crankcase !!

[DZL1]

Great idea. Will do!

[Gwbarm]

From your test it sounds like your valves and rings are leaking. Did you adjust your valves. If they are too tight they could be held open causing your top leak.

[DZL1]

Ok so I finally got the chance to start the teardown. I have attached pics of what I see. The jug looks and feels fine. No grooves. Now the piston top and valves are obviously full of carbon buildup or worse. Not sure if you guys see something I'm not. Also if rings are the culprit, would it be visible or do you need more/better pics of rings? 

 

Thanks to everyone that has offered there help. 

@gwbarm, I did adjust valves to spec before teardown. 

[Mech]

Those rings look to be stuck in their grooves.. That will stop the compression. The piston looks reusable as long as the new rings are a nice fit in the grooves. You check that before fitting them over the piston; you just slip a new ring in from the side then walk it around the piston checking it can't wobble anywhere(or you measure the clearance).

The head gasket seems to be slightly blown, and that may be because the gasket isn't the right one for the engine. There's a steel cylinder liner in an aluminium cast cylinder, and the gasket needs to be getting crimped between the steel and the head. The gasket has a narrow steel "fire ring" on the paper gasket, and that ring has to seat on the steel at the top of the liner. In the picture it looks like the gasket might be off a bigger capacity/bore engine and seating too far out and on the aluminium. It also leaves a little still air gap between head and cylinder where flame can keep burning while the power stroke happens, then the exhaust happens, and for there to still be flame in there when the new fuel starts getting drawn in.. That can cause backfiring and poor power.

The cylinder you need to draw your finger up the bore at the front of the cylinder to see if there is a small lip about 1/4" down from the top. If there is a lip then the cylinder has taper/wear in it and we need to measure that wear. You can do that using the piston and the tip of a feeler gauge and measure at the bottom of the bore and right below the lip where the wear is worst. A bit of wear/taper is ok so if the wear/taper is not too much and you aren't re-boring, then you must remove that lip or it will break the new rings. I'll explain how to remove the lip if needed..  Measure up first.

Edited January 22, 2025 by Mech

[Mech]

To get the old rings out of the grooves you use a small screwdriver to gently wedge the ends of the ring apart slightly, then while you are keeping the wedging pressure on you tap with a screwdriver handle just next to the screwdriver on the ring. It forces a bit or ring out sideways and slightly out of the groove. You do that left and right of the levering screwdriver then use a wider screwdriver to repeat the process but working along the ring a little further out, freeing more ring.. After a while you just push on the end of the ring while tapping any movement along freeing more ring. Putting a bit of fluid on and letting the rings back in sometimes helps free them so the next levering/push/tap moves that section of the ring out readily. You just keep working around the piston working the loosened bit a bit further around by pushing and tapping the ring down in the right place so it causes a bulge out a little further around..

Edited January 22, 2025 by Mech

[DZL1]

Do I need to measure the wear before removing rings?

[Gwbarm]

What you need to do is take the rings off the piston put them in the cylinder one at a time and measure the ring gap it should be between 15 and 19 thousant gap. I still think you should have more compression than that even with worn rings, if broken thats a different story, i would take a closer look at the valves. The exhaust looks like it not seating correctly, could be the angle of the photo but i would check it out. They dont look bad though i have seen a lot worse

[DZL1]

Ok Gwbarm, I will do that measurements. As far as valves go, could I put water and see if the valve leaks? Assuming that it's fully seated. Or is that not a good idea?

[Gwbarm]

You dont have to do that with the old rings, since you are putting in new rings anyway, i just always do to see how bad the old ones are. I do check the new ring gap to make sure it is within specs and if not I know I have cylinder wear.

Water is not the best way to see if valves are leaking, no pressure. When ever i have one torn down this far i go ahead and remove the valves replace the oil seals and clean up the valve and seat good then lap the valves with valve grinding compound to make sure they have a good sealing surface.

[Mech]

So the rings are seized in their grooves DZL ? That will do the no compression, and the oil consumption.

You should free up and remove the rings from the piston before trying to use the piston for a gauge. Once the rings are off put the piston down the bore with the pin parallel to the crank and push it right to the bottom so it's starting to poke out a little, then see which feeler gauge will just go in the gap between skirt and cylinder when you force it in. The feeler will have to bend slightly to fit the wall of the cylinder, so you need to use enough force to do that, and then the feeler should be firm to tight. Try different feelers to see which is the thickest that will go in. Then turn the piston over and push the piston (lined up the same) to near the top, so the skirt is just below that lip, and try feelers to see which one fits there. The difference is the wear/taper. The piston has to be down from the top by enough to get a feeler in, but/and if you buy feelers with tapered ends rather than the half round ended ones, they will slide in far nicer.

You can test valves with fuel which will creep through gaps water doesn't.. But really, it needs valve guide seals, and the valves should be lapped just to see if they are sealing and have nice width to the seat. If they are all good and don't need more than about one minutes worth of lapping to determine that, then it was a small effort to be sure, and if it turns out the seats need more lapping or even cutting, then you will have found that out for yourself without taking it to an expert who will feel compelled to recommend new seats and valves, and guides haha. By the look of the carbon, unless it's rusted from sitting I'd expect those valves to lap in ok.

[DZL1]

Mech, I haven't removed them yet. Planning on doing that today. 

[Gwbarm]

After you adjusted the valves did it help the compression at all.

[DZL1]

No it did not. Pouring oil into cylinder did. It went up to like 48 psi. 

[Mech]

See the rings are stuck in the grooves Gw...  They haven't sprung out..

[DZL1]

Mech, I was able to remove rings very easily. So they weren't stuck. I did the measurements. Piston at bottom of jug had a .014 or 0.35mm gap. Piston at top had a .016 or 0.40mm gap. So a 0.05mm taper gap. Not sure what spec is. You can feel the lip and I have attached a pic about it. 

 

Gwbarm, is this measurement of the piston sufficient or do you still want me to measure ring gaps?

 

Fellas, again thanks for all your time and help. 

[Mech]

Oh well they are very worn out rings then, or overheated. Do they bend easy ? Are they springy ?