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CassidyNZ · 02-07-2019, 19:42

This yarn discusses an event that happened to my motor and led to a “major” modification to the engine. I suspect it is possible for this to occur on any 4JH family engine. I suspect also that this is a very rare event and would not want to spark a wave of re-powering jobs

I’ve not heard of another one.

So first let me explain the part of the engine in question.

When the block is cast and machined, the tunnel that the camshaft runs in is bored with decreasing bearing sizes front to back so that the camshaft can go in easily but with every bearing correctly sized when it’s in place. Hope this makes sense. At the back end of this tunnel is a frost plug that blocks end of the tunnel. The last bearing in the tunnel has oil pressure that squeezes out both sides of the bearing (front and back). The frost plug stops the oil there and returns it to the sump. So far so good.

At the front of the camshaft is a plate that sets the camshaft endfloat (prevents it from moving backwards and forwards). On my engine, this plate wore excessively and allowed the camshaft to move backwards in the engine. Please don’t ask why that happened, I have no explanation. With only a tiny amount of clearance between the end of the camshaft and the frost plug, the camshaft leaned against (and spun against) the plug and eventually the plug overheated and welded itself to the camshaft.

At that point the plug spun in the hole, destroying the perfect face that a new plug would need to be leak-proof. So installing a new plug was not a solution. And that’s where the “major modification” came in.

The aluminium bell housing on the back of the engine has a cut-away exactly where the frost plug is. So if you look at the back of your engine, you will see the plug at the upper left side. Look for signs of bluing from heat. If you see the signs, remove the timing cover at the front of the engine and check the camshaft endfloat plate for wear.

My mod was to remove the bell housing, weld in an aluminium block to fill the cut-out, machine it to the face of the bell housing and cut a ring in the new face for an O-ring. With the standard gasket on the bell housing and the O-ring on the new extension, I achieved oil-tightness by simply bolting the whole lot together.

Removal of either the bell housing and/or the timing cover requires that the sump also comes off because they all have a common gasket and not renewing the sump gasket will only result in more oil leaks. Don’t ask me how I know this

I have some pictures of the modified bell housing but they are not on this device. I will retrieve them and post them in another post.

Hope this info hasn’t scared the bejeesus out of anyone - I think I may be a one-of-a-kind in engine-related failures

**Wotname** · 02-07-2019, 20:11

Looking forward to seeing the pics!

CassidyNZ · 02-07-2019, 20:15

The attached pictures show the area that has to be created to the same level as the engine face. The large pic shows the cardboard template I made to form the aluminium block that would be welded in place. I can’t recall the thickness of the plate but it was about 3mm thicker than required to allow for machining. The machine marks visible under the template are the casting webs and other irregularities having been machined off.

I cut the block out of ali plate, massaged it to a decent fit then welded it to the bellhousing. The second pic shows the face machined back to the engine face. What I haven’t got is a final pic of the finished job with a ring cut into the new face for an O-ring that mates to the back of the block.

This mod was done back in 2009 and remains leak-free. After several oil changes, I have found no traces of aluminium in the oil or the filters, indicating that the camshaft is not wearing the inside of the extension.

Perhaps the whole failure was not caused by the camshaft moving rear-wards but by a trainee technician knocking the frost plug in too far during original assembly. You never know . . .

Of course, now that I look at my pictures, you will not be able to see this part of the engine until the bellhousing is removed. So hope yours is not a candidate. You’ll know when you see a stream of oil over your starter motor

**Wotname** · 02-07-2019, 22:23

Quote:

Originally Posted by CassidyNZ

........
Perhaps the whole failure was not caused by the camshaft moving rear-wards but by a trainee technician knocking the frost plug in too far during original assembly. You never know . . .

........

Nice work

, did you do all the machining / welding etc.

You suspicions for the root cause holds some merit; especially as there seems no reason for the camshaft moving rearwards.

CassidyNZ · 02-07-2019, 23:00

Quote:

Originally Posted by Wotname

Nice work

, did you do all the machining / welding etc.

I did all the machining but my ali welding is not that great so a friend welded it for me.

Quote:

Originally Posted by Wotname

You suspicions for the root cause holds some merit; especially as there seems no reason for the camshaft moving rearwards.

Yes, what got me thinking that is that if the cause was abnormal wear, the engine should have totally failed by now. It has run for much longer since the failure than it did before it.

**a64pilot** · 03-07-2019, 06:45

The gear on the end of the cam that drives it is I assume a helical cut gear to keep noise down, if so then of course this is the source of the thrust, there is of course something that is supposed to prevent lateral movement of the cam, it’s wear is I think the cause of your problem.
I’d just guess that either it was oil starved by a blocked passage or improperly heat treated to begin with.
Either one should be hopefully a one in a million failure, and if a blocked oil passage, I hope it got unblocked.
My guess is a bad part, as the failure hasn’t reoccurred.

Of course you know you saved the motor, any normal average mechanic or Yanmar service center would have told you the block would have to be replaced, and then you would start running numbers and likely re-powered.

redsky49 · 03-07-2019, 07:00

How many engine hours when this occurred?

stormalong · 03-07-2019, 09:31

Quote:

Originally Posted by redsky49

How many engine hours when this occurred?

That's what I want to know too.

CassidyNZ · 03-07-2019, 13:24

Quote:

Originally Posted by a64pilot

The gear on the end of the cam that drives it is I assume a helical cut gear to keep noise down, if so then of course this is the source of the thrust, there is of course something that is supposed to prevent lateral movement of the cam, it’s wear is I think the cause of your problem.

The cam gear is heat shrunk onto the camshaft with the thrust block in-between so changing the thrust block is not a simple job. Essentially the whole valve train has to be disassembled to get the cam out, then the process of separating the gear from the shaft.

Quote:

Originally Posted by a64pilot

I’d just guess that either it was oil starved by a blocked passage or improperly heat treated to begin with.
Either one should be hopefully a one in a million failure, and if a blocked oil passage, I hope it got unblocked.
My guess is a bad part, as the failure hasn’t reoccurred.

Because of my description above which is only part of the strip requirement, I never replaced the thrust block, what was in there is still in there. Hence my leaning towards poor assembly rather than component failure. The engine is still running as one would expect it to. I suspect the camshaft is still located exactly where it should be.

Quote:

Originally Posted by a64pilot

Of course you know you saved the motor, any normal average mechanic or Yanmar service center would have told you the block would have to be replaced, and then you would start running numbers and likely re-powered.

Yes I do know that - I am a budget sailor and spending $20k on a fixable problem, for me, does not compute.