2 Stroke Lesson

[bertsmobile1]

Bandit, Tough it's not a match, but not a surprise . I looked at some online flywheels and there are lots of them which kind of look alike but.. $18-$80 yikes. So check carefully the dimensions I sent. You say go and I will send you a USPS track no. to the address given, no charge, no big deal.

Berts, Good tips. So a good US plumbing store will have the drain tracer? You did not mention if you do crack checking on customer machines??

No you will have to buy the dye penetrant spray from a bearing shop or engineering supply store.
The dyes are the same that funny limey yellow or yellowish red but the kit has them dissolved in a very light oil with very high surface tension so it will wick into the cracks & be drawn out by the developer ( spray talc ).
There are two types of dye penetrant test kits, UV or visible light and now I come to think about it, then shop chain named "plumbers suppy" down here keeps the visible light kits .
The dye , sodium or patassium floroscene is bought as a powder. It is a very powerful dye.
To does a dain you put a match in the powder, tap the loose dust off the match then drop it into the water good for several thousand gallons.

 

[motoman]

Berts, Great to have the pros reveal secrets. Curious if such crack detection is a regular check during rebuilds such as aluminum heads. valve seats, shafts?

 

[bertsmobile1]

No,
did it regularly when I was a metallurgist , but that was another life.
Even went to colledge & got some secondary diplomas in various methods of NDT.
I regularly check used con rods & crankshafts I fit to vintage , veteran & classic motorcycles
Never bothered with mowers as the cost of replacement parts does not warrant it.
I just fit a new part if anything is suspect.
Usually when you strip an engine it will tell you what is happening, all you have to do is look carefully at each part before as & after it comes off.
then degrease the parts properly and look again. look carefully at all the other associated parts
The only part I would bother to do a dye pen check on a mower is the crank.
If I have to spit the cases then the engine will get new rods on both the piston & counterweight as these two parts together is less than the labour cost in disassembly & reassembly.
No customer will kiss my ###### for saying them $ 35 on a $ 350 rebuild.
But all of them will kick the same part of my anatomy, vigeriously should I get it wrong and the rod fails after a $ 325 rebuild.

Blue smokes are dead easy you just pump them up & suck them down.
If I suspect a crack I pump them up in a tub of water, you just have to go to the trouble of making proper blanking off plates for the inlet & exhaust.

Dye penetrant testing will only confirm the surface integretity of a single item.
It will show you the head is cracked around the valve guidebut it won't show you that the head is leaking around the valve guide.
Mower valves are not under enough stress to suffer from stress cracking.
Cracked valve seats will show up when you lap them and again, a leaking seat is not detectable you can only find a physical crack in a single piece.
So you could dye pen check th head after you had installed the seats to verify that you had not cracked the head installing them, but that would be really rare.

Remember we are dealing with very low stressed lazy engines in a very low state of tune.
If you are doing 54Hp 500cc single cylinder motorcycle then things are a bit different.
However a 15 Hp 435cc mower engine is not in the same country let alone the same ball park.

nearly all of the internal engine problems on mowers ( excluding blown head gaskets on inteks ) can be traced back to low / no oil.
After that it is vibration from out of balance blades
followed by fractures caused by hydraulic locks

 

[motoman]

Again thanks for your comments. Regarding failure mechanisms in ? air cooled lawn related engines. Is "low oil" the same as "heat kills?" You did mention cowling important in thermal design of the rig (reminds me of VW. My measurements and others' experiences show these engines running 280F oil in summer and I have measured 304 F on the head. This is on its way to 380F where the aluminum starts to creep (soften). The intek pushed an exhaust guide which I theorized was softened aluminum losing grip. Whadda ya think?

 

[bertsmobile1]

Again thanks for your comments. Regarding failure mechanisms in ? air cooled lawn related engines. Is "low oil" the same as "heat kills?" You did mention cowling important in thermal design of the rig (reminds me of VW. My measurements and others' experiences show these engines running 280F oil in summer and I have measured 304 F on the head. This is on its way to 380F where the aluminum starts to creep (soften). The intek pushed an exhaust guide which I theorized was softened aluminum losing grip. Whadda ya think?

I would not think anything untill I saw everything.
Most times guides shift in the head it was due to bad fitting in the first place usually combined with insufficient clearances and possibly overheating to boot.
Valve guides are not under any real stress if the floor is machined nice & square.

Now as for your numbers some where some one has got their units mixed up .
400 deg C is where you should start to worry not 380 F.
This transittion temperature will also vary greatly depending upon the exact alloy being used.
heads are generally Al-Si-Cu-Mg alloys with controlled Fe.
Strictly speaking Fe is an impurity in Al casting alloys as it readily forms Fe-Si which are really hard & brittle.
However scrap Al is cheap & has high Fe content . Fe will form a high strength skin on the surface of the mould so facilitates clean & early stripping so die casters keep it as high as permissible depending upon the actual Si content.

As a home project it is worthwile to do a guide but as a work shop job again not cost effective as the price of a new head is less than the parts & labour to fix the old one.
You will need to rebore , note I said bore not drill , out the old guide hole and get an oversized valve guide you need a .002" to .005" interfearence fit.
This oft requires some lathe work as I have never seen oversized guides.
'The other alternative is to build up the guide hole and bore it out to suit the std guide.
You will see a lot of people recommending some sort of epoxy , Some times you get away with it some times you don't .It is a bit too hot for most epoxies.
You could also try some thing like loctite high temp bearing retainer.
Home owners can get away with these sorts of repairs because if it fails, tough luck but not the same if you are taking some ones hard earned so it is a new head for me.

Inteks have a big design flaw in that the bridge between the pushrod chamber & the cylinder is too thin for the position of the head bolts.
It really needs another one in the middle of this section or a lot more metal.

 

[motoman]

When the Intek came apart I spent some time reviewing online data. The 380F figure came up repeatedly as creep temp. Also there was not a problem with the fit dimensions of the guide /bore based upon .001-.002" fit. The guide was removed , measured, and refitted only to move again. Briggs does not sell replacement guides forthe Intek V 24, only complete head assemblies. Aftermarket fans are popular for AC bikes like Harley whose rear cyl is prone to overheat in slow moving traffic. I looked for locktite able to withstand head temps and could not find any.

 

[bertsmobile1]

When the Intek came apart I spent some time reviewing online data. The 380F figure came up repeatedly as creep temp. Also there was not a problem with the fit dimensions of the guide /bore based upon .001-.002" fit. The guide was removed , measured, and refitted only to move again. Briggs does not sell replacement guides forthe Intek V 24, only complete head assemblies. Aftermarket fans are popular for AC bikes like Harley whose rear cyl is prone to overheat in slow moving traffic. I looked for locktite able to withstand head temps and could not find any.

That is the big trouble with Dr Google.
Some one makes a mistake.
22,000 people who have absolutely no idea repost the item with the mistake in it because they think it makes them look good on the web and google picks up the garbage because it works basically on the force of numbers.
Remember that old joke from prep school " eat S..T 40,000,000 flies can't all be wrong"

The Aluminium Developement council has an excellent web site which lists the bulk properties of most commercial alloys .
But insead of giving information from known expert domains top priority Google goes for paid positions then numbers so counts the repostings higher than the experts.

Now as for your guide.
every time you pull a guide you take some of the head out with it.
So as a rule of thumb you should never put the old guide back in.
The process I use for guides is to heat in an oven to 350 deg C for about /2 hour, pull the head out & drop it onto blocks covered with an old blanket .
Spray the guide from the inside with some of that liquid freeze you get from electronics stores followed by a sharp tap if necessary as they oft fall out under their own weight once you hit them with the freeze spray.
I have a big set of guide removers & replacers but I have found they do more damage than they are worth on alloy heads.

Replacing guides is same process.
Heat head. freeze guide on the drift you are going to use to insert it theo put of the oven out of the freezer and tap tap tap.

 

[motoman]

More good info for home enthusiasts. But the creep point of Aluminum was verified on several engineering sites and the same 380-390 F came up for the point at which aluminum begins to soften. Dr Google or no, these sites were not forums like this one. Other supporting evidence of softening is auto head rebuilders who perform scratch test of incoming heads for repair and reject "soft" ones. I was going to have the Intek Brinell tested , but decided not to as very little readership was interested. The reinstalled guide was a dubious experiment and when it moved again I believe it was due to the weakened aluminum head. When I stand back and look at the little Intek head I wonder if it needs more finning? Finally I have seen guides with metal O rings , but I think they were topside. What's your take?

 

[Grassbandit]

I finally got my hands on the correct flywheel! But the saga isn't over, my new dilemma is installing the springs that make the pawls on the flywheel move when you pull the starter rope. How do you install them?

 

[Grassbandit]

I finally got my hands on the correct flywheel! But the saga isn't over, my new dilemma is installing the springs that make the pawls on the flywheel move when you pull the starter rope. How do you install them?

Ok I got it, there's a little trick involved and some measure of patience. Once I got it all reassembled I ran into another issue with the clutch eating the plastic recoil housing so I corrected that by putting a bigger washer under the clutch and now its all good.
thanks everyone for sharing knowledge.