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JP3 smoke from cylinder heads, after putting in new pistons and rings


DannyD

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Hi guys, I have replaced the 3 pistons with new ones with pre-installed piston rings. Further more I had to replace one liner.

The first time the engine started quick and sounded good, but after some time running it started to give light coloured smoke form the cylinders heads.

When switching it off and starting it a couple of times, it starts much worse every time.

It looks like there might be to much compression or something.

Has anyone got a clue?

 

 

regards Danny

 

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Light smoke from hot parts on a newly worked on engine is not rarer, it is just oily had marks or reservation fluid burning off. As for the rest of your post I am not experienced enough on such engines to give an opinion, but did you check the bump  clearance between piston and head upon reassembly, assuming it needs doing on that engine.

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Where is the smoke coming from? Are the changeover valves screwed in or out? If they aren’t seated properly it’s quite possible for them to let by…and the loss of compression makes starting hard or impossible. 

  • Greenie 1
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Just now, DannyD said:

The valves have been taken out and polished and should be ok. But it makes sense what you are saying.

Make sure they are well screwed in when starting. The spring washers can lose their “spring” then the valves slowly open when the engine is running. Once the engine is running screw them right out and see if that helps..the exhaust may smoke a bit more if the engine is lightly loaded. 
 

See if you can see where the smoke is coming from…will make diagnosis easier. 
 

Also there are/were some dire headgaskets around…mainly from India. They gave the wrong bump clearance and also the asbestos inner was made of cream cheese and quickly failed. 

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First thoughts are exhaust manifold gasket, maybe head gasket or some other exhaust joint but that does not explain the poor starting, with 3 cylinders it should start OK on just two I'd have thought. I think a bit of time with a straight edge and torch checking the flatness of the block and liners and compare top dead centre on the three pistons night be an idea but its not an engine that I know. A quick edit, If the valves (any of them, changeover  or inlet /exhaust)  have been removed I would wonder about them too. maybe valve covers or rocker box whatever a JP has are filling up with smoke from up the valve stems and compressiom is a bit iffy

Edited by Bee
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4 minutes ago, Bee said:

First thoughts are exhaust manifold gasket, maybe head gasket or some other exhaust joint but that does not explain the poor starting, with 3 cylinders it should start OK on just two I'd have thought. I think a bit of time with a straight edge and torch checking the flatness of the block and liners and compare top dead centre on the three pistons night be an idea but its not an engine that I know.

The liners need to be raised slightly from the block…the measurement is in the manual…this helps make a better seal on the head gasket. I had all sorts of issues with a liner sitting a bit low. 

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Not much oil in the rocker area, I believe it needs to be kept wet, at least mine did. ;)

 

Looks to me as if the smoke is  coming from the decompressors.

Edited by Loddon
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47 minutes ago, Tracy D'arth said:

There is no oil pump I believe so the rockers depend on oil mist to lubricate them. So its maybe oil mist you are seeing and you need the rocker covers on to ensure lubrication?

I know a friend with a JP3, I'll ask him tomorrow.

Ok thx I hope he has an answer. 

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1 hour ago, Tracy D'arth said:

There is no oil pump I believe so the rockers depend on oil mist to lubricate them.

JPs certainly have an oil pump which feeds the main bearings and big ends. On some engines there is also a pressurised oil feed to the ends of the hollow rocker shafts. But not on the one in the video, although you can see the holes in the heads where the oil feed would be connected.

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The smoke looks like residue oil or grease burning off. It would have really useful to have seen the other side of the engine especially the changeover compression valves. 
The rockers etc are lubricated by splash technology, and grease.
Sounds very good after that rebuild.

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2 minutes ago, David Mack said:

JPs certainly have an oil pump which feeds the main bearings and big ends. On some engines there is also a pressurised oil feed to the ends of the hollow rocker shafts. But not on the one in the video, although you can see the holes in the heads where the oil feed would be connected.

Sorry I left the word "supply" out!  I remember my friend telling me that the rockers were not fed with oil from the sump.

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3 hours ago, RAP said:

The smoke looks like residue oil or grease burning off. It would have really useful to have seen the other side of the engine especially the changeover compression valves. 
The rockers etc are lubricated by splash technology, and grease.
Sounds very good after that rebuild.

 

Would also be good to have a video without the camera being moved about. Say 30 seconds with the camera dead stationary in several positions looking at the engine from each side and from each end, would make it easier to divine where the smoke is coming from. 

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You have a JP3 which should have grease lubrication to the rocker shafts. You don't and need to fit greasers before you damage the shaft. From the video I would suggest that you check that the changeover valves are not venting through the hole in the valve body which is a sign of the valve not seating properly. Also look to see if there is any bubbling between the head, gasket and block. JPs are a little prone to weeping which is sometimes due to the head not being tightened properly or,if you are unlucky, warped heads or block face. Try pulling the head down first. They are pretty robust engines but the heads can be problematic at times

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On 18/11/2021 at 18:03, steamraiser2 said:

You have a JP3 which should have grease lubrication to the rocker shafts. You don't and need to fit greasers before you damage the shaft. From the video I would suggest that you check that the changeover valves are not venting through the hole in the valve body which is a sign of the valve not seating properly. Also look to see if there is any bubbling between the head, gasket and block. JPs are a little prone to weeping which is sometimes due to the head not being tightened properly or,if you are unlucky, warped heads or block face. Try pulling the head down first. They are pretty robust engines but the heads can be problematic at times

This engine has been running without greasers for over 10 years, there seams to be no wear and tear on the rocker shafts. Are you sure this is necessary?

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36 minutes ago, DannyD said:

This engine has been running without greasers for over 10 years, there seams to be no wear and tear on the rocker shafts. Are you sure this is necessary?

My friend with a JP3 has no oil feeds to the rockers and never greases them either. I think that the oil mist coming up the push rod holes in the heads is what you are seeing and that is the lubrication that has so far not let you down.

 

But then its not my engine and I could be wrong, often am.  No responsibility taken if the advice is wrong as I make no charge.

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My recall of these engines is the head pools oil to the tops of the pushrod tubes ....and then the valve springs throw the oil up to rockers .....valve springs are very weak too,so load on the rockers is minimal.

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It is greased lubrication for the rocker shafts on JPs, all were built with it. Later JKs  are oil fed. My junk bin has lots of worn out JP rocker shafts in it from engines that were not greased properly.  We always convert JPs to oil feed when we restore them.  Way better to have the JK set up.

  • Greenie 2
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On 23/11/2021 at 11:09, steamraiser2 said:

It is greased lubrication for the rocker shafts on JPs, all were built with it. Later JKs  are oil fed. My junk bin has lots of worn out JP rocker shafts in it from engines that were not greased properly.  We always convert JPs to oil feed when we restore them.  Way better to have the JK set up.

It’s really not a hard job though to grease the rocker shaft & top the oil up…for me it’s part of the joy of owning a vintage engine rather than a digger power plant 

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