Cleaning piston heads

[HarryO]

Hmmmm.....

Didn't think so...

I thought you were a bit hard on Yakka.

(Group Hug)

Thats all..

[marshy]

As a qualified motor mechanic with 18 years experience including lots of engine & gearbox overhauling I would have to say that I agree wit BM.
2 stroke outboards are a whole different ball game to motor cars. I have rebuilt 1 outboard engine for myself & assisted with one other for a friend. These rebuilds were for pleasure ,not profit as outboard are not my field. In doing these rebuilds I learned a lot about the contruction & design of these motors. I purchased factory engine mauals for both engines & the manuals say quite clearly NOT to remove any more material from the heads than necessary & in fact describes the use of emery paper on a glass surface.They also say that in the normal course of an engine rebuild that The bearings do NOT need to be replaced unless they show signs of excessive wear from water incursion of lack of lubrication shown as
corrosion pits or dark discolouration on the crank journals . I know BM doesn't need anyone to defend him but I just thought I would put my 2cents worth in .

Merry Christmas
Marshy

[HarryO]

I agree with you, Marshy...

The two are similar, yet so diverse..

Cleaning the head surface on glass is a standard, but
if I caught one of my apprentices using 120 dry they would
get a very swift kick in the backside.

Start with 220 wet, finish with 400 wet. NOTHING ELSE.

BM, which engines don't have single use STT rod bolts?

[Roughasguts]

We gone and lost Smelly, where are you and what's happening, with that motor.

Got that bolt out yet? Try the tighten loosen bit with plenty of lube, you can even place your electric soldering iron on that bolt, then hit it with some good penetrant after you get it as hot as possible.

But if you snap the head off, Oh well join the club, bloody surprised you didn't snap one removing the heads.

Almost a waste of time those easy outs, But you have to start drilling the hole out anyway.
Start off nice and small after a center punch belt, or use a small die grinder stone to flatten out the stud that's left, the slightest angle on the broken stud will deflect the drill bit.

If the stud has broken below the thermostat housing great use that same size drill bit to be dead on center to use as your pilot hole.

Thing is you have to know when to stop drilling depth wise

"Nick any ideas how deep"
Maybe the same depth as the 2 other bolts you got out?????

Also you need to be 1.5 mm less in diameter than the original stud.
That be so you can run your tap in there and have a desent thread.

Run your tap in your Battery drill at a fairly slow speed, go in until it slows then run the thread out, and in again Use plenty of WD40 to clean out the thread as you go.

New drill bits mate, best quality as well, otherwise well you know.

[Roughasguts]

You know I was thinking about the 120 grit, this would leave a scratchy surface more so than me 800. "Maybe better"

So I think the 120 would be better for the gasket and whatever goo you use, so the gasket has the best adhesion, compared to a shiny surface.

Never had a problem with a creeping gasket before, but a rougher surface always gives better adhesion.

[lippa]

i agree with the trade certificate thing. i have no peice of paper, but i do own and operate my own spraypainting company. i just can't have an apprentice. but i can have plenty of "trainee's" go figure that one.


cheers

lippa

[FNQCairns]

Reading through the thread BM did say "effectively" in his original statement.

Love it when a group hug comes together

[finga64]

Some of the best tradies I've ever seen and worked with haven't a ticket on the wall and some of the worst, clueless idiots have.
It's all about passion and committment to the job. What-ever it is.

[BaysideMarine]

Harry,

Many engines pre around 1990 didn't use stretch bolts on the conrods.

The manual in all cases will indicate if a particular engine needs to have them replaced.

Many mechanics replace them as a matter of course, however it really isn't necessary. A close inspection with a magnifier for any minor cracks is sufficient to deem a bolt re-useable.

I was talking to a mate of mine recently (mechanic with a ticket on the wall) and I had just finished a 100hp Merc rebuild (1991). This has stretch bolts fitted. He had rebuilt one 6 months earlier and had re-used the stretch bolts...... oh dear...

80hrs on and the customers engine is still running fine. But he did agree with me that it might be best to strip it down quickly at its next service and toss in some new rod bolts........

So I guess when in doubt, replace the rod bolts. At about $5 a bolt it doesn't break the bank to change them.

RAG, goo on most headgaskets is not a good thing.

Lippa, yep thats the only thing that annoys me is the inability to have apprentices. Good cheap labour is hard to find...

And yes, where are you Smelly??

[Kerry]

So who does things the "accepted text book" no grease/goo on studs/bolts etc or who lightly greases gaskets and bolts etc

Be honest now

Regards, Kerry.

[finga64]

I'll go first Kerry.
I use some crap called Hylomar on head gaskets before assembly. Always.

Crap on the bolts depends where they go and what they do.
Conrod bolts etc ...didley squat (except if the book says something completely otherwise for some strange reason).
Head bolts; if going into water jacket some gasket goo (not normal gasket goo but some stuff Holden uses on their head bolts) around the thread to the head and some under the head of the bolt. I do this mainly to try and stop any corrosion of the bolts and to protect the thread a bit.
if not going into water jacket I simply follow the book procedure but usually bung a bit of the goo under the head so as to seal the bolt-head to whatever surface.
Come on. I'm bending over...shoot me down.....

Good point though Kerry as a lot of people do different things just out of habit. Some are good practices and some are aren't (I'm been polite there )
Cheers Scott

[Roughasguts]

I clean threads, blow them out, smear grease them as well.

Goo all me gasketts, never with copper based stuff, and most me head gaskets. To seal them against the minute amount of salt water,
Then prevailing salt build up which causes gasket failure.

If you look at a aircraft engine no oil leaks, if you find one it gets taken out of service.
Why no leaks sealer everywhere.

[dogsbody]

Where is Smelly?, this is better than any book ive read we've had good verses evil other people taking your eye of the plot, mystery, entrigue can't wait to see the ending. Roll credits

Dave.

[yakka]

hi bm
only ever used micrometers and dial gauges when measuring things to do with the reco of an engine. we would reco the motor and dyno tune and test it. 12 L bus motors, d9, small single cylinder generator motors, side valve motors, bue print racing motors lots of motors.
got the manual out for my motor a 60 hp yamaha (I know, not a Johno)
it is a Clymer Shop manual 2-250 2 stroke 96-98, page 360 shows a picture of them hand surfacing a cylinder head. i read on and it is only done if head warpage is measured and less than .1 mm or 4 thousandths of an inch using 600 wet and dry on a surfacing plate. then machining is the alternative. never said not be careful as matter of fact said be careful.
reckon thick glass would do well , not ever convinced a piece of timber would.

now I know this is not a johnson but should be similar specs.

again for the yamaha page 318 good practice to replace needle bearings on rebuilds

when reconditioning motors we would not put an odd sized piston in. all the time and expense was in getting the motor out and striping it down and was a pointless exercise in saving what was a small amount of money when compared to the entire job.

I'm not saying it hasn't been done and done successfully but was not practiced where I worked.

I would not do this to a car I owned because of the way I learn't and I wold not do it to a boat motor taking me and the crew out to sea.
nothing said here will change my mind on that one.

this is from the world of motors outside of the marine. a head that is machined flat does not guarantee a proper seal with the head gasket when bolted back together if the finish on the head is rough. It might not seem much but depth of the finish if too deep was enough to allow a path of escape for the compressed fuel mix and lead to early failure of the head gasket. 120 grit would be in that class for these motors.

its beer time and enjoy reading the differing views all from differing perspectives.

[BaysideMarine]

Hmmmm.....

Didn't think so...

I thought you were a bit hard on Yakka.
(Group Hug)

Thats all..

Yeah, I agree...

I get quite passionate about my trade....

My unreserved apologies Yakka for having a dig.

Cheers,

Nicholas