Oversize Piston in Open Type Recip. Compressor

[imranmd]

Someone can let me know the consequences of using oversize piston in open type reciprocating 4 cylinder Bitzer Compressor. The compressor model is 4T(.2). The cylinder bores become tapered and clearances are out of limit. Therefore, I want to use oversize piston in new bore sizes.

[Brian_UK]

An oversize piston is liable to seizure.

You need to get the bores honed out to suit the size of the larger pistons.

[Samarjit Sen]

Please do not use oversize pistons. By using them you are asking for trouble. It is not only liable to sieze, but the crank shaft may crack. I know a number of people in our country who tried this and damaged the compressors. Finally it was found that replacing the compressor would have been cheaper.

[The MG Pony]

An oversize piston is liable to seizure.

You need to get the bores honed out to suit the size of the larger pistons.

Thats exactly what he said he's going to do, bore it out then use a piston one step up. very common here from 3,000HP (BIG mofo engine!) marine engines to 2 stroke weedeater engines to compressors.

[US Iceman]

Boring engines is fairly commony for increasing displacement or providing straight cylinders. On industrial compressors you can replace the cylinder sleeves with new pistons and you get a "new" compressor.

Smaller compressors that do not have removable sleeves may have other problems as Samarjit Sen stated. In addition, you could possibly have problems with overloading the motor.

[Brian_UK]

Thats exactly what he said he's going to do, bore it out then use a piston one step up. very common here from 3,000HP (BIG mofo engine!) marine engines to 2 stroke weedeater engines to compressors.

Well excuse me if I misread the post

[The MG Pony]

Sorry, didn't mean any thing by it, just pointing it out nicely. *Hands a beer* common mate, we all miss things now en then!

[GHAZ]

Hello imran i,ve built hundreds of compressors and i have,nt come across any oversized bitzer pistons and rings for 4T models. But in Pakistan you can have most things custom made, if you rebore all the bores about (30 thou ) you would be o,k.If you wanted to go bigger than that then make sure the suction reed is long enough to reach the pocket across the cyclinder.

[Samarjit Sen]

If you are reboring the compressors and putting oversize pistons , you are increasing the dispalcement, which in turn increases the load on the compressor. The power compressor too increases. All these leads to disbalancing of the system and specially more load on the crankshaft.

In case there are piston sleeves, change the sleeves and put back the orizinal sized piston. That would be better. There are so many large companies all over the world who are remanufacturing the compressors. No one puts oversize pistons.

US Iceman's comments are worth listening to.

[absrbrtek]

The increase in capacity is negligable IMO. You would have to be in a lab under test conditions to notice the difference. We are only talking 20 or 30 1000ths here. JMHO

If you are reboring the compressors and putting oversize pistons , you are increasing the dispalcement, which in turn increases the load on the compressor. The power compressor too increases. All these leads to disbalancing of the system and specially more load on the crankshaft.

In case there are piston sleeves, change the sleeves and put back the orizinal sized piston. That would be better. There are so many large companies all over the world who are remanufacturing the compressors. No one puts oversize pistons.

US Iceman's comments are worth listening to.

[Samarjit Sen]

The refrigeration compressor is the heart of the system. Even by making the smallest changes there is a change in the performance. In refrigeration there is nothing as negligible, what changes or deviations you make you have to ensure that under no conditions the performance should be effected. What ever controls, pipe lines etc you are subsequently selecting is based on the compressor capacity. The more careful and precise you are in selecting the various components, the better performance will you get.

Another important thing in this particular case is, that please try to find the reason as to the deformation of the piston bore so that it could be attended to, and it does not occur again.

[suny]

I agree with Mr. Samajith on his advice, but as the Bitzer 4T.2 is an Open type compressor. If you do not have any other option other than to use an over sized piston, you should reduce the revolution of the compressor to match the original displacement.

Suny

[absrbrtek]

OK. I have used plenty of rebuilds with oversized pistons, undercut cranks etc. Never had any performance issues. Y'all must be engineers and have limited to no field experience. I guess on paper the few extra BTU's the compressor will pump makes a huge difference, in the real world it does'nt mean squat. JMHO

I agree with Mr. Samajith on his advice, but as the Bitzer 4T.2 is an Open type compressor. If you do not have any other option other than to use an over sized piston, you should reduce the revolution of the compressor to match the original displacement.

Suny

[US Iceman]

Never had any performance issues. Y'all must be engineers and have limited to no field experience.

My guess is you jumped to a conclusion. I think most of the people on the RE forum are field people 100% of the time, or have worked in the field over many years.

Minor differences are of course negligible. However, I would much rather start off with a warning of what can happen so everyone understands the ramifications.

If we said, OK, that's fine don't worry. Someone will take the advice to an extreme degree and then say: "They" said it was OK.

A couple of minor details have a way of combining into one big mess, and that is straight from field experience.

[Samarjit Sen]

My company is over 50 years old, and I have been in this for over 44 years now. In my earlier years , I made it a point to work with my technicians in the field so that I may have a practical experience. Even today other than designing a system or doing othr office works, I personally make it a point to visit the sites and if there is a problem discuss the same with the technicians and if can not get a solution come to the forum.

There are engineers who other than theoritical knowledge also posses practical knowledge. Specially in refrigeration there is nothing as minor. These minors and negligible grows and becomes large, when it is too late. I tottally agree with US Iceman's views.

[Paulajayne]

Balance !!!

Do one - do them all.

Paula

[Samarjit Sen]

I am not trying to offend any one. In our country we have firms who are rebuilding the compressors. They use all genuine parts and stick to the original dimensions. They do not compromise on any components. Whereas there are people who rebuild compressors and reduce the cost compromise on the quality and the work. These compressors work for a few weeks and it is beyond repairs by them.

[suny]

Hats off to US Iceman & Samarjit

Suny

[old gas bottle]

no major points to be scored here for sure, but i do think if anything that a small overbore would benifit a old system in helping things go around a bit quicker assuming the crank was good to start with ,which is doubtfull as wear and tear would be spread around a bit if you follow me,normaly the crank gets worn first through low or old oil,bad protection etc,but with all old systems that leads to other things,like the motor cant hack it,the odd leak appears etc,but then again if the condensers are are old and blocked etc ,that will bring more problems, dont you just love the trade ?

[absrbrtek]

For the disbelievers that oversized pistons and undersized rods are used heres some links:
http://www.bradparts.com/cartgenie/p...t.asp?scat=171 for rods.

http://www.bradparts.com/cartgenie/s...sp?category=25 for pistons.

Note that just about every compressor without replaceable liners has oversized pistons available. These are routinely used in the remanufacturing process. Again, .010, or .020 oversized will not make a difference on a 2", 2.5" or a 3" piston. These are used so the blocks can be salvaged.

You guys can't tell me with your 100's of years of combined experience that none of you have never pulled a head off and saw .010 or .020 stamped on top of a piston indicating it is oversized? And if you pulled the head off the compressor, it had been running in that application for years. I am sure the inspection was not done because you suspected the piston was oversized and causing system problems.

Unless you pull the heads off, look and measure the piston, you will never know it is oversized. JMHO

[Samarjit Sen]

There is no arguments regarding using oversized pistons etc. All are free to adopt their own practice and with what they are comfortable.

I am not used to this nor do I advice any one.

Please do not feel offended, we are here to share our views.

[old gas bottle]

i dont dissagree matey at all, not only that, there are plently of manufactures that use one size body with differant bore sizes for cappacity selection,same crank and rods just differant drive motor,valve reeds etc,what i am saying is there would be no point in changing the pistons +10 say and just re-shelling the crank without getting it back to its manufactures tollerances,its either half a job,rings,shells and gaskets etc, or proper rebuild,boring,grinding,new major components etc, when all said and done its not a racing engine !

[Samarjit Sen]

I fully agree to that. In such cases the connecting rod, the crankshaft etc are all designed for higher ratings. These compressors could be operated with different size pistons and rpm to give higher displacement and thus higher capacity.

[john doersom]

For our milk tank farm customers over the years, I have bored and sleeved quite a few of the old Dunham Bush open compressors. Never had any failures from our work.

Most were 5hsp and larger.

By boring the block to receive a sleeve, if no sleeves were installed originally, you are able to use the same size pistons, rings, etc. Never had any crankshafts to break. Most of the problem originated with broken valve scarring the cylinder walls.

Make sure that the new pistons are within 2 grams of weight of each other or else the compressor will not be in balance.

[GHAZ]

It will more cost effective to buy a new 4t bitzer compressor, because the chances are it,s goeing to need total rebuild ie crank regrind, under size mains bearing ,new rods for the big end journels, rebore or sleave,pistons , shaft seal, its not worth overhauling its only a small machine.

[absrbrtek]

I myself have never used oversized pistons. I wouldn't waste my time. With the labor spent putzing around with it, you could have bought a remanufactured compressor that comes with a warranty. JMHO

There is no arguments regarding using oversized pistons etc. All are free to adopt their own practice and with what they are comfortable.

I am not used to this nor do I advice any one.

Please do not feel offended, we are here to share our views.

[Samarjit Sen]

Hi john doersom,

You rebore the compressors and put a new sleeve of the size of the original piston. But do not use oversize piston. I hope I understand what you said.

My contection has been that using oversized piston is not good for the compressor.

[TXiceman]

I think the increase in displacement is minimal. Problem will be getting over sized pistons and over bored rings for the application. You sure do not want to put standard rings in an over bored hole.

ken

[sylvester]

the choices is acceptable 20T oversize is allowable just make sure condensing unit could handle noticeable rise in temp

[john doersom]

Some time ago I stated that we used to bore the cyl. and sleeve the old Brunner and Dunham Bush open compressors that we used on milk tank installations. Never had any problems.

In fact, during the early 1940's it was quite common to rebuild rather than replace equipment. During those times replacements were not available.

Dunham Bush used to provide the necessary pistons and sleeves for field rebuilding.

I don't think, though, that by boring the cylinder for a larger piston is worth the effort. However, sleeving the cylinder and sticking with the orig. piston size is OK.

Blitzer equipment was never heard of in my part of the world. But, the milk still had to stay COLD.

The max. bore is generally only .040 in. I think sleeves are still available for this size bore.

When installing a new sleeve, be sure to use "LOCKTITE" skeeve glue, or else the sleeve might move in the cylinder. The sleeve must be keep in the freezer ovenight before attempting to install in the cylinder.