Assessing a used Yanmar 8HP diesel engine

[Wotname]

Check for rust / corrosion / scale in the block just around the area near the O'ring closest to the water side.

Without the O'rings in place, the clean liner should slide easily into place. With the O'rings fitted and lubricated, the liner should push into place with a firm hand force.

[HorseshoeBay]

Thanks Wotname!


Too tired today, and will need to remove the new liner to place the o-rings.


I couldn't understand where exactly the grooves for the o-rings are in the outside of the liner?

[HorseshoeBay]

Photos after liner removal

[Wotname]

Originally Posted by HorseshoeBay

Thanks Wotname!


Too tired today, and will need to remove the new liner to place the o-rings.


I couldn't understand where exactly the grooves for the o-rings are in the outside of the liner?

Compare the old and new liners to see where any grove in the liner might be. If the liner is an aftermarket item, it might not have grooves in it. My aftermarket YSE liner didn't have grooves.

If the liner doesn't have groves, just place the supplied O'rings in the grooves in the crankcase. See red arrow on picture. Use some grease to hold them in place and also lubricate the liner outer surface around the area where the the o'rings sit with oil to ease the liner past the O'rings.

[Compass790]

What Wottie shows in pic of block is where the o-rings go. You dont fit them on the liner you fit them in the block & then push liner in. Ditto what he says about greasing the liner & o-rings ( I like silicone grease) or EP90 gear oil will do.


You have to place the rings level/square in the liner not on the piston to measure ring gap. Best to use piston ring pliers to remove them. Just file the ends if gap too small.

[HorseshoeBay]

New o-rings were held into the grooves with grease and the liner was inserted.


I ran a finger around under the liner lip that projects into the crankcase for any sign of a snagged o-ring.

[HorseshoeBay]

Wondering about the pushrods.

My memory on removing them 6 months ago is hazy, and the manual could be clearer.

Do they go through the head under the non-valve ends of the tappers?

[Compass790]

Originally Posted by HorseshoeBay

Wondering about the pushrods.

My memory on removing them 6 months ago is hazy, and the manual could be clearer.

Do they go through the head under the non-valve ends of the tappers?

Yes but under non v/v ends of rocker arms & be careful to engage the ends of the tappets & dont drop in crankcase as its a PITA to rescue them.
Good you got liner in ok.
My tip is to use some kind of gasket sealer on head gasket when re-assembling as you will have far less trouble if you do. Something like permatex 51813. These are 23:1 compression engines prone to head gasket leaks.

[HorseshoeBay]

Have a Sunity head gasket, which looks to have copper inserts.

One side has a form of embossing and the reverse side is flat.

Wonder about the orientation?

Seeking advice on how best to reassemble the head, with the head gasket and torquing of the head bolts. Have read some YouTube comments about allowing an hour between initial partial tightening and further tightening.

I don’t have a torque wrench!

In a YouTube video, Permatex warns against using their products on head gaskets.

[skipperpete]

Times have changed regarding head gaskets, now with modern engines we have monotorque head gaskets that already have a coating on them so no other additional treatment is required beyond perfectly clean and smooth surfaces on the block and head, particularly around the liner top. Older engines often have corrosion and imperfections around the waterways and block surfaces that aren’t easily sealed by an ordinary gasket and some have no sealing at all around the pushrod galleries so it’s perfectly reasonable to give the gasket a bit of help in these areas. Permatex still makes the spray on copper gasket sealant that was originally labeled as being for head gaskets and I suspect that the alloy heads, blocks and hi tech head gaskets of todays modern engines motivated the rewording of the permatex advice….. on a Sunity gasket fitted to a single cylinder raw water cooled engine , a little bit of permatex might be useful.
You should borrow a torque wrench and why not have a break between consecutive re tensionings, it can’t do any harm to have a smoko break between the steps (and if you ever get to pull the heads down on an NT855 Cummins you really need to sit down and get your breath back between the increases)…. I prefer to just pull em all down with 3 progressively increasing torques in a diagonal pattern or to the workshop manual diagram, but monotorque or not, I always re tension the head after the engine has a few hours on it, usually by backing off the head bolt a third of a turn and smoothly pulling it up to the specified tension…. But only one at a time, never more than one and never if using template tensioning or hydraulic tensioning.

[mcpusc]

when i had the head off my YSB8 a couple years ago i re-torqued the head nuts after using the engine, maybe three or four times. the first couple times there was quite a bit of slack on the exhaust side after the heat cycle, but then it stopped loosening up.

i used the permatex copper spray on the gasket — it seems to work fine. no leaks so far!

[Wotname]

Originally Posted by HorseshoeBay

Have a Sunity head gasket, which looks to have copper inserts.

One side has a form of embossing and the reverse side is flat.

Wonder about the orientation?

Seeking advice on how best to reassemble the head, with the head gasket and torquing of the head bolts. Have read some YouTube comments about allowing an hour between initial partial tightening and further tightening.

I don’t have a torque wrench!

In a YouTube video, Permatex warns against using their products on head gaskets.

While it hard to be precise without seeing the gasket, I would be inclined to put the embossed side towards the block i.e. not against the head. This is because the head surface should be flat. The block side is not flat. The liner should be protruding from the block by about 0.2mm (~8 thou). The embossing should take up this gap around the water and pushrod galleries.

[HorseshoeBay]

At TDC, the piston appears to protrude a little above the liner.


The head flat surface has been scrapped and sand papered, still leaving some of the original fine texture and marking.


Considering lightly sanding it with very fine grade sand paper.


I wonder about how close the liner should get the surface of the head and whether that should align to create a partial seal, further sealed by the head gasket.


Does anyone know the standard head gasket thickness when it is compressed in place?

[Wotname]

Originally Posted by HorseshoeBay

At TDC, the piston appears to protrude a little above the liner.
.......
Does anyone know the standard head gasket thickness when it is compressed in place?

Have a look at the thickness of the old gasket compared to the new one.

Lay the old gasket on the block and see if the piston protrudes past the gasket. I suspect it won't.

[Compass790]

I still stand by what I said about using gasket maker/cement on head gasket.
This is from experience with your engine & selling parts for the same.

You can buy digital torque wrenches quite cheap & resell again on gumtree or a used torque wrench. I'd say your chances of getting a leakfree seal without a torque wrench & no sealer are very low.
Yes the piston comes above the top of the liner but does not come above the steel flame ring of the gasket as Wottie says, at least if it is torqued at spec,