OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines removing stuck/crumbly head gasket from ptorques?

Hi guys,
picked up a powertorque off the strip to try and get it going.

The o ring under the starter was shot so that was replaced but the compression still did not feel as tight as it should have been. (judging by the trusty yank cord mechanism :P)

I have had a look and the bore looks brand new (piston and rings look excellent as well).

I wanted to check the head gasket and i think i have a problem...

The gasket cam off in bits n pieces, crumbly at parts and plain stuck on in other parts.(feels like its stuck so tight!)

Without resorting to scrapers/ blades, how do you guys remove the old gaskets and prep the surface for a new gasket installation?

Thanks!

i use a paint scraper or a grinder fitted with a sanding wheel. Rough but if you are careful works well.

I use a knife blade, or a square-ended scraper. I use the knife blade where the adhesion is not all that strong - it slips under the pieces of gasket. I use the scraper where the gasket has bonded completely to the head or cylinder, and can only come off in the form of dust.
I don't use a grinder because I'm a bit heavy-handed, and I remove too much aluminium or cast iron if I go that way.
When I've removed just about all the gasket, I scrape the surface in the normal way with the square-ended scraper. I have to resharpen it several times just to do a single cylinder mower engine. Even with all the resharpening, it only takes 3-5 minutes to clean up both surfaces.

thanks guys, ill give it a shot tomorrow. in terms of placing the new gasket on, does it need any grease/lube or does it go straight on?

one way i have found effective is the wire brushes you use in your high speed power drill. i use them for everything, especially gaskets. it will also leave a good shiny face for the gasket to sit against, making sure there is no rust left.
regards jay

ok, new gasket installed.
I have also cleaned out the carby (for good measure).

I gave the cord a yank and it still feels like some compression is missing....

Anyways, I decided to give the mower a shot at starting.

I was yanking fairly evenly and had a backfire or 2. A couple of brisk pulls (i mean VERY brisk pulls) and the damn thing started running.

Now...

The machine did not sound right (not like any mower i have heard before) but it did respond well to throttle controls. Also, it seemed like the vibration was a little excessive.

I did not keep it running for long (as the neighbors would have lynched me running it at this hour). But when i switched it off, i could not get her started again...

Im hoping anyone can chime in as to what the next step is? Or is this as good as i might get the machine to be?

What exactly is there left to replace if the compression is unsatisfactory? (i think its just the bottom end crankshaft bearing?).

Also, could this low compression be contributing to the unusual sounding mower?

Any help would be appreciated. Again, as stated before, piston rings and piston seemed tight and in good nick.

With nearly all two strokes, the air and fuel mixture is sucked in through the crankcase so you have "crankcase compression" - you should feel resistance to pulling the starter twice per revolution, compared with once every second revolution for a 4 stroke. If the crankshaft-to-crankcase seals leak, or the piston doesn't fit the bore well (scuffing, striations etc.) the crankcase compression will be very weak even if the piston rings are in good condition.

I suggest you check whether you have a pronounced crankcase compression as well as a cylinder compression each revolution. You should also measure the piston ring gap if you haven't done it.

There are many things other than loss of compression that could be causing the symptoms you have described.

I do feel the resistance twice per revolution, its just that the resistance seems quite weak. (im also asuming that the difficulty with which i started the motor also had to do with insufficient compression).

From what i could see the piston and bore looked excellent (better than my full crank and my other powertorques which run like a dream), i guess i will pull out the piston and inspect it carefully.

Also, i have not swapped the decompressor around to check if it might be the cause of the low compression (something i guess i should have done earlier).

I will keep everyone updated.

Again, any tip or areas i should look at would be greatly appreciated.

If you are familiar with the compression feel on similar engines (that use the same starter), then the weak feel is a useful clue. As you say, the decompressor is a likely problem area and should be swapped to see if it makes a difference. If you pull out the piston, remove the rings and measure the ring gap with them in the bore near the top. You should do that anyway if you are tidying up the engine, so it won't be wasted effort. Have you checked the crankshaft seal and bearing at the bottom of the engine? The roughness and noise you reported could be due to a failure of that bearing. If the bearing is loose and wobbly, the seal can't work.

Usually it makes sense to start by checking the spark and whether the engine will start easily if you prime it. We have tried to follow a shortcut by paying attention to the base engine before we look at the more common problem areas: the ignition and carburetion. It isn't a waste of time if you are going to keep the mower, because the base engine needs to end up in good shape anyway, whether or not the engine is running well when you check it.
When you report back on the current round of checks, please let us know what the spark looks like, whether you are using a new spark plug, and whether it starts easily if you prime it.

Johnno, pull the decompressor out (19mm spanner) and screw a spark plug into the decompressor hole, then give the pull starter a pull and that will give you an idea of the compression, you maybe surprised.

To test the decompressor in your hand, suck on the plastic tube end and watch the plunger suck in and keep sucking you should not be able to suck anymore.

Hey guys, im back...

I guess i should have clarified the "weird noise". The engine sounded like a putt putt boat (as in you could really hear the cycles).

I also should have clarified that i have checked the basics at the start (compression, spark and fuel) and i was only really missing compression. (spark was nice n blue).

I swapped the decompressor for one which i know is fine and lo and behold, start on 2nd pull (and sounding fine).

I have not checked the bottom end crankshaft seal/bearing but have not noticed any oil/fuel leaks (and plus the engine sounds fine with the different decompressor).

MVC, the decompressor 'spark plug test' was also performed, it still felt loose compared to my other powertorques when doing the same thing ( i could get it to turn ).


One thing i am concerned about is the presence of a slight backfire at the engine start (and the presence of a spark which seemed to have flown out of the carby manifold, but i am not 100% sure about that). I have not checked the seal from the manifold to the cylinder (i assume a gasket or o-ring exists for this?).

I am also assuming that this could also play a role?

Is this the correct part for replacing? (im not looking for the carby to manifold o-ring, but the seal between the manifold and the cylinder).

https://www.outdoorking-forum.com.au/index.p...mp;cPath=193_514_225&products_id=597

The symptoms are not a good match for weak mixture. If you can hear it firing individual shots when it is running at governed speed, it is four stroking or eight stroking, which is more likely to be poor scavenging than lean mixture. However if you have not checked both of the intake tube O-rings, which are notorious for leaking on older Powertorques, you should do so.
A spitting from the intake pipe when you run it with the air cleaner removed would probably mean lean mixture. A popping or banging in the muffler might mean leaky piston rings or incorrect ignition timing. The timing is not adjustable, but you should check that the magnetic pickup has the correct gap from the flywheel, and is not loose or badly earthed.
If you can't rock the blade plate or move it radially even a small amount, the crankshaft bearing is probably OK.
My suggestion is that you may have moderately weak compression, and the only cause left that you haven't checked, is worn piston rings (excessive ring gap). That could cause leakage of partly burned gas into the muffler (with possible popping sounds). Power would be less than normal, and starting would be harder than normal. If it has leaky rings you need to fix it or it will score the piston and sludge everything up.

So, replace the one remaining O ring (the second one in the intake pipe) and check the ring gap. At that point you should have a good base engine. If it does not run properly at that point, the next thing to investigate is the carburetor - but I think leaky rings are a better fit for your symptoms.

had a wiggle of the piston, it did seem a tiny tad loose. I have changed the piston rings and it has helped with comression. All just swap over the decompressor and that should be it!

thanks fellas! (1st time doing an engine overhaul basically, was not as hard as i thought it would be).