Cleaning piston heads

[BaysideMarine]

Many head gaskets are self adhesive and adding a sealing compound (unless explicity indicated in the manual) is a very unwise idea and can lead to premature gasket failure. I never apply a sealer to a head gasket.

All head gaskets will leech salt out in a salt water environment. Thats normal and to be expected. Thats why they should be changed every 5 years (not that they ever are).

Rod bolts I usually use Loctite Stud Locker on them.

Head bolts go in dry along with all other integral powerhead bolts.

Crankcase halves are smeared with Loctite master gasket sealant.

Lower unit, waterpump housing and powerhead bolts get the treatment of nickel anti seize grease.

Cheers,

Nicholas

[BaysideMarine]

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 (1)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 (2)

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. (3)

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. (4)

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

Hi Yakka,

No agro, just putting a marine angle to your above post.

Hilight 1) Clymer or Seloc manuals are not well regarded in my trade as a suitable manual. They are a hybrid of a genuine workshop manual and things are often inaccurate and incomplete. A genuine workshop manual is important for marine engines. I don't know why it has worked out this way but the aftermarket manuals are so so different from the genuine. Perhaps its the same in the auto trade???? I dont know. Thats your area.

Hilight 2) I believe you will find that statement to be quite unique to your manual. If you ring Noel Aaorns (the former Merc National Service Manager) he will advise you that direct from Mercs engineers in the US that needle rollers do not require replacing for an engine rebuild and are only considered of no use when damaged by water (or perhaps excessive heat).

Hilight 3) Fitting an oversized piston is absolutely normal, common, everyday, routine (hope thats clear enough ) practice in the marine trade for 2 stroke engines. The replacement pistons are balanced in weight to the originals and there is no problem whatsoever. I understand this is not done in an automotive engine and fair enough, thats your trades thing. But in my game its definitely NORMAL and doesn't not harm an engine at all.

Hilight 4) Understand your point, but after reassembling many engines (checking comps at time of rebuild of course) and then servicing them 12 months later (and again rechecking comps) they show the same compression and no sign of water ingress to the cylinders or compression blow by into the water jackets (which usually will aerate the water around the head/s and cause overheat warnings).

Cheers,

Nicholas