heat piston to properly put in wrist pin?

[texasgeezer]

My Kubota engine is a d1302-DI. The service manual I've been using has information for a d1402-DI. Virtually all the parts are the same with the D1402 having the sleeve bored & honed for the larger pistons.

I am replacing the #2 piston & the service manual said to 'heat the piston in oil" before inserting the pin.

In an attempt to have this done 'properly' I took it to a local mechanic that has '35 years' experience working on trucks, cars, tractors, etc...

I told him what I wanted & he said he would do it for me. When I went to pickup the rod & piston assembly he told me 'he was unable to press the pin in so he took it to a machine shop & they honed it so the pin could be pressed in'. He said he never tried to heat it, 'cause he had never had to heat one before'.

So my question is:

Is honing to fit (without heating) a proper way to fit the pin?

- One local 20 miles away dealer said the piston should be heated.
- One dealer 15 miles away said they press fit without heating.
- Two local popular machine shops said they never heat the pistons anymore. If they don't readily press in 'they hone them'.
- A national engine rebuilder said they always heat them.

So I'm confused. It seems if any material is removed by honing that would be that same as wearing over a long period of time & would decrease the useable life of the piston & would fail sooner.

When I look at the 'acceptable tolerances' it appears that some pistons & wrist pins would 'slip together' while other pistons & pins would have a little bit of interference that might require heating.

What I think is that most of the local guys that do this type work have found that honing & without heating is 'good enough'.

Any thoughts?

 

[Apogee]

So I'm confused. It seems if any material is removed by honing that would be that same as wearing over a long period of time & would decrease the useable life of the piston & would fail sooner.

Sounds like you've found guys who are used to primarily working on gas engines.

I think your analysis is spot on. It will be more critical with a diesel due to combustion pressure. It's roughly 2.5x higher than a gas engine combined with ignition that works by "pinging" to fire. Both factors add extra stress to the pistons. Kubota would not go to the extra step of heating the pistons if they didn't feel it was necessary.

Your "mechanic" should have called you first before having the piston honed.

Biggest concern I'd have is the pin moving around because it's not as tight as it should be once things warm up and the aluminum piston expands while the pin size stays fairly constant.

Steve

 

[lsmurphy]

I think you are buying a new piston.


You don't have a press?


Heat the piston slowly in an oven.........use qt coffee can with enough oil to cover the piston. Freeze the pin in freezer over night.

And work fast.

 

[lsmurphy]

Further.......

You replace one, you replace them all.

Contact the national company that heats them and ask for a quote if they replace all three pistons, install the rods, and send them back to you.

You came this far and went cheap.........just don't get that.

 

[texasgeezer]

Thanks for the 1st two posts. Didn't really care for the third, but doubt if he expected me to appreciate it. Guess he didn't think about any way that the other two could be new or 'good as new'. Personally I was concerned that Kubota might be sourcing parts from India or China so their profit could be higher.

I didn't include background information since my intent was to make people aware that 'professional' service companies do not necessarily give professional service. Four of the five local companies in this scenario think that their version of doing this task is 'good enough'.

Sort of like going to the doctor seeking their help & they tell you live with the cancer since something else will probably kill you first.

I realize that , to them, their method will probably give no failure for many, many, hours. But it does seem that it would contribute to rod bushing failure & also shed metal into the engine oil. Little things done wrong can result in serious consequences.

 

[lsmurphy]

Thanks for the 1st two posts. Didn't really care for the third, but doubt if he expected me to appreciate it. Guess he didn't think about any way that the other two could be new or 'good as new'. Personally I was concerned that Kubota might be sourcing parts from India or China so their profit could be higher.

I didn't include background information since my intent was to make people aware that 'professional' service companies do not necessarily give professional service. Four of the five local companies in this scenario think that their version of doing this task is 'good enough'.

Sort of like going to the doctor seeking their help & they tell you live with the cancer since something else will probably kill you first.

I realize that , to them, their method will probably give no failure for many, many, hours. But it does seem that it would contribute to rod bushing failure & also shed metal into the engine oil. Little things done wrong can result in serious consequences.

First off, Kubota is sourcing their parts, some of their parts anyway, to China. This is no secret.

Secondly, I have no expectation of appreciation from anyone, you can take it for what it is worth.

No, I did not take your post as being a complaint regarding 'professional services'. I took it as someone altered your new piston and took it out of spec and now you have a dilemma.


As to the other two looking new............

You did not state how many hours on your engine but you are replacing a piston due to some sort of failure........Yes? No?

By the time you get done I assume you will have about $500 into this repair? New piston, rings, gaskets, oil and other............surely you are having a valve job done while you have the head off????? Not to mention your time?

It's called fatigue.........what do you got? 2000 hours? 3000 hours? apparently it ran long enough for something to give......right?

So, If one gave, how much longer before another goes? and you do it again?

 

[Tx Jim]

I wonder if freezing the wrist pin in lieu of heating piston would allow for installation?

 

[bandaidmd]

I always thought the pin was held by the connecting rod or it floated and was captured by clips in the piston. I guess I never worked on one that the piston pin was a press fit into the piston. I have seen machines to heat the rod for pin installs.

Sent from my DROID RAZR using Tapatalk 2

 

[texasgeezer]

For: bandaidmd

I am for from an 'expert' but from my recent research most engines use one of three common methods for dealing with the wrist pin.

1. floating in the upper rod bushing, tight in the piston holes (rod bushing relies on oil to keep from wearing)
2. floating in the piston holes, tight in the rod bushing (piston should have pin holes that are treated or 'bushed' & rely on oil to keep from wearing)
3. floating in both the piston & the rod bushing (both rely on oil to keep from wearing)

The kubota engine that I'm working on has the 1st method, so it seems that the tighter pin fit in the piston the better for long term wear.

I've attached a picture of the new piston & one of the old pistons. Plus a picture of one of the old rod bearings. I believe you can tell that the old parts show little wear. It might be because of the dark background but, to me, the old piston appears to have better definition of the oil ridges than the new piston.

My main fear is getting crud into an oil passageway & not knowing about it. But since I care, I can take my time to try to do it right.

 

[bmisch01]

I've been a diesel mechanic for 27 years , & have rebuilt meny differnt engines , full floatng pins will push in by hand, and will have retainers to hold them in place interferance fit pistons , must never be honed out or have the pin pressed in it will damage the piston & you will pull it back apart very soon. if the machine shop honed out hte piston pin bore they ruined your piston , it wont be very long before you start hearing the pin rapping, the best way to assemble the piston is to place the pin in the freezer overnight if possible or at least a few hours , place the pisto in a pot of boiling water for 10 min. you will see that the pin will fall right in with no effort, sorry that you have to buy a new pitson , hope this helps you

 

[Russell King]

I wonder if freezing the wrist pin in lieu of heating piston would allow for installation?

Either will work but most people will do both (heat hole and chill shaft) to maximize the clearance between the parts and increase the working time to install the shaft.

Heating alone may be enough, Chilling alone may be enough. Getting the shaft halfway into the hole and getting it stuck is not a good place to end up! Therefore, most people will use both to maximize chance of success.

 

[Apogee]

Texas, you might consider a set of rod bearings while you have it this far apart. While your bearings do look good, an extra thou in clearance can make a big difference in oil pressure when warm and idling.

Also, take a look at how the bearing has worn. The rods usually wear into a slight oval and that is what you're seeing on the bearing wear. That's why the marks on the bottom (and I'm also assuming the top) but not the sides. Mic everything and if anything is borderline, just have the crank ground and the rods resized. It will live a lot longer that way.

Plastigage is your friend here.

Steve

 

[lsmurphy]

Texas, you might consider a set of rod bearings while you have it this far apart. While your bearings do look good, an extra thou in clearance can make a big difference in oil pressure when warm and idling.

Also, take a look at how the bearing has worn. The rods usually wear into a slight oval and that is what you're seeing on the bearing wear. That's why the marks on the bottom (and I'm also assuming the top) but not the sides. Mic everything and if anything is borderline, just have the crank ground and the rods resized. It will live a lot longer that way.

Plastigage is your friend here.

Steve

I've been a diesel mechanic for 27 years , & have rebuilt meny differnt engines , full floatng pins will push in by hand, and will have retainers to hold them in place interferance fit pistons , must never be honed out or have the pin pressed in it will damage the piston & you will pull it back apart very soon. if the machine shop honed out hte piston pin bore they ruined your piston , it wont be very long before you start hearing the pin rapping, the best way to assemble the piston is to place the pin in the freezer overnight if possible or at least a few hours , place the pisto in a pot of boiling water for 10 min. you will see that the pin will fall right in with no effort, sorry that you have to buy a new pitson , hope this helps you

I'm wondering if he has the old mindset of small block Chevy 'refresh' for under $200?

Both of you are correct. But I wonder if he'll listen?

I've rebuilt several gassers in my years but never a diesel, one of these days I'll tear into one, look forward to it.

My concern, one that I tried to express, is using fatigued parts (pistons in this case) and reintroducing them back to factory compression of around 450psi.

 

[texasgeezer]

Don't know why I should have put a long narrative about my tractor to ask a simple question about heating pistons.

The cost, the wear (or lack thereof), comments about 'going cheap', 'you replace one you replace them all', have nothing to do with my question.
You make comments that don't fit the question. It muddies the water & takes away from the intent of the thread. If you are going to post on a thread don't assume anything that is not commented on. If you really want to know for just general conversation - ask questions.

So I guess I'll muddy the water myself:

In my case I got different estimates for rebuilding the engine. They ranged from $3000 to $5500. I can buy a complete tractor for those prices. Machine shops would not let me source the parts. It is a low hour tractor that overheated due to internal corrosion of the front engine aluminum cover letting a little antifreeze out under pressure. The previous owner let it go a long time without changing the antifreeze.

I decided (since I'm 70 years old, on a limited budget, don't use a tractor much, never rebuilt an engine, have other interests, want to keep the wife happy) to try to make an equivalently good tractor by replacing the piston that was (lightly scored & barely rubbed the cylinder wall).

I read extensively about honing (grit sizes, pattern, oils, bottle brush type, bar type). Decided to buy a good bar hone. Also bought good tool to measure diameter of the cylinders to check wear & my honing. Cylinders were still almost new spec.

Doing the work in the frame. Decided to also replace all rings & rod bearings & bushings. Should leave just the mains & seals. Much cheaper than having someone pull the engine & rebuild it.

If it fails soon after I put it back together, then I'll pull the engine & rebuild with the bigger pistons called for by the d1402 engine or buy a similar model & keep mine for parts to use or sell.

A few of the things (I think) I've learned in my research:

- the work is easy, learning how to do it better/right takes time

- bottle brush type hones do not fix out of round or taper problems (a lot of people use this type because they are cheap & easy to use, can fix ring problems temporarily).

- honing good cylinders (in spec) in a used engine should be avoided
(study done by Michigan University). Engines showed less wear & still seated the rings than engines that had been honed. Cylinders of honed engines showed more wear & bearings showed more wear.

- if honing of (in-spec) engines is done just barely break the 'glaze', intent is to reduce embedded particles that are not removed by cleaning.

- it appears that the inner cylinder runs hotter. Kubota supplies a different piston for their industrial version for the #2 cylinder. On a rebuild (for my engine series) I would make the #2 cylinder a tiny bit bigger than 1 & 3.

- don't blow air into the open water passages with the head off. It blows the deposits everywhere including the oil passages.

- buy the drill or air tool "Scotch-Brite™ Roloc™ Gasket Removal Disc Pak 7714, 2 in x NH A MED" for gasket removal. Take it easy, it works quickly.

- avoid delays once the head & oil pan is off - would keep it cleaner

- plan to change the oil & filter a couple of times during the 1st few hours of run time ( to try to get rid of honed particles & crud that might have got in during the work).

- a secondary 2 micron oil filter would almost eliminate wear from particles in the oil. Bypass less than 10 percent of oil through second filter. I plan to research how to do this on my tractor & the Prius once it gets out of warranty.

- new light weight oils can provide more useable horse power, but do not protect against wear as well. It is a trade off.

- dealers send a lot of the work out to a machine shop

- mechanics are just people, some are good, some are not so good, check around & ask questions. No matter how bad they are, it will probably run for a while (long enough that you can't blame them). Ask them to double check the critical items. Give it a good workout soon after getting it back.

- messicks.com has good parts manuals

 

[Kubota Newbie]

Tx'geezer (btw, like the handle)

Dealing just with the original question....

It'll probably be ok. Your pin is a floating design and is held in place by the wire circlips. The pin is not held in place by the aluminum piston. My WSM says the same thing, heat the piston and "tap" the pin in (but not press). The pin is still going to have clearance and move/rotate some when the piston is hot. EVEN WITH that assembly instruction the WSM for my Kubota allows a little over a thousandth clearance cold - pin to piston boss. So if they honed it to the normal half a thousandth or so you'll be fine. The question is really just how much clearance you end up with at running temp.
Look... if a floating pin will stay put in a blower motor running at 10,000 RPM or better it will be fine in your little Kubota. You could ask them, but my guess is they put just enough clearance on it to hand press it into place as is the normal practice. In which case things will turn out just dandy. Go Mow & Be Happy!

 

[texasgeezer]

Thanks for the comment about it will be ok if floats a little. I'm going to have a machine shop take the pistons off & check the piston to pin clearances. Though, I do hate to take the chance for possible damage due to handling.

When I compared the factory spec for new components, it showed an allowable 'boss/hole' to pin of -.45 thousandths to +.47 thousandths. So it does appear to be ok to have the pin 'float' a little. Personally I'm going to ask the machine shop to make sure the wrist pin is not floating in any of the pistons at time of re-assembly.

Kubota built such a strong engine I believe it will stand up quite well. If it fails it will be my fault for not keeping it clean enough. Too bad the crank can't be removed without splitting the chassis.

 

[efharg]

I worked as a mechanic for 40 years on all types of engines, diesel and gas.

I never heard of anyone honing pistons to get the pins to press in. (That's just stupid.)

I always heated the pistons in hot water, and the pins would slide in with no problem at all.

 

[Apogee]

Texas,

Just wanted to say thanks for taking the time to do your summary post above. It provided good background info for this thread, but is applicable across the board. There is a lot of good info there!

Perhaps the mods might consider making it a permanent sticky someplace on the forum, or perhaps we ought to consider a new thread with general tip info like this.

Excellent!

Steve

 

[BAP]

Texas, I wouldn't be afraid to just fix the one piston and another other parts you see fit and can afford, then put it back together. I farmed for many years before I got hurt, and more than once, we had diesel engines in either tractors or trucks that developed wrist pin troubles. We would replace the bad one and put it back together. We had one truck with a Cat motor that developed trouble at about 15,000 miles. Dealer replaced the wrist pin and it ran for close to 30 years after that. Another tractor lost one at about 3,500 hours and it was replaced and we traded it at 11,000 hours still running fine. Yes in ideal world with unlimited budget you would redo the whole engine fresh like new. But, with today's prices, and low incomes, you do what you have to and don't look back. Good Luck and trust your judgement.