MARZ 2.5
02-13-2011 | 08:41 AM
#2
RE: MARZ 2.5
I think quite a few folks have taken them apart already. To check for swarf and so on.
It appears one has the luck of the draw as to how good of a engine they get when they get one.
One thing mentioned in this thread below, is removing the crankshaft and re-tempering it to help prevent premature breakage.
http://www.rcuniverse.com/forum/m_98...tm.htm#9839919
I happen to have a couple of them too. I plan on running them one of these days. if I wind up finding a small OS .10 carb or something like it, I might try converting one to RC use as well.
It appears one has the luck of the draw as to how good of a engine they get when they get one.
One thing mentioned in this thread below, is removing the crankshaft and re-tempering it to help prevent premature breakage.
http://www.rcuniverse.com/forum/m_98...tm.htm#9839919
I happen to have a couple of them too. I plan on running them one of these days. if I wind up finding a small OS .10 carb or something like it, I might try converting one to RC use as well.
02-13-2011 | 09:39 AM
#3
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RE: MARZ 2.5
For everything you ever wanted to know about the MARZ (and quite a lot of stuff that you probably didn't!), check out the article at:
http://www.modelenginenews.org/ad/marz.html
The MEN website is a great source of information on a lot of classic diesels as well as restoration tips, etc. Use the "Finder" menu under "Engines" to access these articles.
I've had quite a few of these engines in my time and still use one regularly. The most impotrtant issue to be aware of is that the shafts tend to be brittle and sometimes break in service. You have to normalize them through appropriate heat treatment to deal with this. It's all in the article.
Good luck with your MARZ! A good one is a really nice engine.
http://www.modelenginenews.org/ad/marz.html
The MEN website is a great source of information on a lot of classic diesels as well as restoration tips, etc. Use the "Finder" menu under "Engines" to access these articles.
I've had quite a few of these engines in my time and still use one regularly. The most impotrtant issue to be aware of is that the shafts tend to be brittle and sometimes break in service. You have to normalize them through appropriate heat treatment to deal with this. It's all in the article.
Good luck with your MARZ! A good one is a really nice engine.
02-13-2011 | 10:50 AM
#4
RE: MARZ 2.5
ORIGINAL: controlliner
Has anyone taken apart a MARZ 2.5 cc diesel to examine the quality of machining?
Has anyone taken apart a MARZ 2.5 cc diesel to examine the quality of machining?
It is a question about the material quality with respect to the hardening method and the material is available where the engine was produced, some time the material was selected who has similar properties as a high quality material, however, is as durable as an engine that was produced by high quality materials.
The model engine in USSR was not allways produced in same factory, some time the engines was produced in school as an education in metal work and sold as a product.
Use the model engine nicely and you will get a great joy of your model engine.
02-13-2011 | 05:40 PM
#5
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RE: MARZ 2.5
Taken a Marz apart?
Yep been there, done that and all following Adrian Duncans advice in Rons Model Engine site.
Some of the items not mentioned there are the pistons crown could do with a polish up for two reasons, one, it has signifcant swirl marks left from machining that would carbon up rapidly and two, the apex of the crown will collide with the contra piston well before the rest of the crown would and relieving it would enable a higher compression rate and most probably a better gas flow as well.
Ialso -
Cleaned out the three cylinder jacket hold down screw threads with a tap and installed slightly longer screws, this stops the screws from walking out under running conditions,
Replaced the bearings with Japanese ones (long story but it was instructive),
Ditched that awful prop for an 8x4 APC,
And relieved the contra piston as it was very tight.
Good luck with it. Mine at the momement has a propensity to start backwards all the time and the obvious solution of going to a larger diameter propellor may be good on the test bench but hardly helps in the air!
Yep been there, done that and all following Adrian Duncans advice in Rons Model Engine site.
Some of the items not mentioned there are the pistons crown could do with a polish up for two reasons, one, it has signifcant swirl marks left from machining that would carbon up rapidly and two, the apex of the crown will collide with the contra piston well before the rest of the crown would and relieving it would enable a higher compression rate and most probably a better gas flow as well.
Ialso -
Cleaned out the three cylinder jacket hold down screw threads with a tap and installed slightly longer screws, this stops the screws from walking out under running conditions,
Replaced the bearings with Japanese ones (long story but it was instructive),
Ditched that awful prop for an 8x4 APC,
And relieved the contra piston as it was very tight.
Good luck with it. Mine at the momement has a propensity to start backwards all the time and the obvious solution of going to a larger diameter propellor may be good on the test bench but hardly helps in the air!
02-14-2011 | 08:21 AM
#6
RE: MARZ 2.5
My first one had a tight fit that caused binding between the conrod and the rotor. The solution was to use a thicker rear gasket...works fine.
Also, low compression seal at first. Compression seal improved wiith running.
George
Also, low compression seal at first. Compression seal improved wiith running.
George
02-14-2011 | 09:11 AM
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RE: MARZ 2.5
That's because cast iron pistons actually expand a little over the first few dozen heat cycles. This is why you have to run an iron-and-steel piston/cylinder combo properly - there are no short cuts. For more information, check out the article at:
http://www3.telus.net/dieselcombat/about_diesels.htm
http://www3.telus.net/dieselcombat/about_diesels.htm
02-14-2011 | 04:50 PM
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RE: MARZ 2.5
ORIGINAL: gcb
My first one had a tight fit that caused binding between the conrod and the rotor. The solution was to use a thicker rear gasket...works fine.
George
My first one had a tight fit that caused binding between the conrod and the rotor. The solution was to use a thicker rear gasket...works fine.
George
The drama for me is getting the thing to run forwards!
02-15-2011 | 01:55 PM
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From: SydneyNew South wales, AUSTRALIA
RE: MARZ 2.5
ORIGINAL: earlwb
Does anyone happen to know what the bearing sizes or part numbers are for these engines?
Does anyone happen to know what the bearing sizes or part numbers are for these engines?
Make sure that the front bearing is sheilded with the shield facing forward, it just gives added protection from dirt ingress.
Cheers.
02-15-2011 | 03:39 PM
#11
RE: MARZ 2.5
ORIGINAL: earlwb
Does anyone happen to know what the bearing sizes or part numbers are for these engines?
Does anyone happen to know what the bearing sizes or part numbers are for these engines?
02-15-2011 | 06:33 PM
#12
RE: MARZ 2.5
Thanks I was hoping someone had already done it and remembered. I hate to pull apart a engine and then wait a week or two to get new bearings before I can put it back together again. I am always afraid I'll lose some little tiny part or something. I am still impressed with KMOT for when he tore apart that radial engine and after a long time, many months, was able to get it back together again.
02-16-2011 | 03:47 PM
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From: SydneyNew South wales, AUSTRALIA
RE: MARZ 2.5
ORIGINAL: earlwb
Thanks I was hoping someone had already done it and remembered. I hate to pull apart a engine and then wait a week or two to get new bearings before I can put it back together again. I am always afraid I'll lose some little tiny part or something. I am still impressed with KMOT for when he tore apart that radial engine and after a long time, many months, was able to get it back together again.
Thanks I was hoping someone had already done it and remembered. I hate to pull apart a engine and then wait a week or two to get new bearings before I can put it back together again. I am always afraid I'll lose some little tiny part or something. I am still impressed with KMOT for when he tore apart that radial engine and after a long time, many months, was able to get it back together again.
Any bearing supplier worth his salt should have stacks of these in stock, from what I recall the rear bearing is 7mm ID but that hardly helps here.
02-17-2011 | 02:01 PM
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RE: MARZ 2.5
Mate I just Googled Grapevine Texas Bearing Suppliers and got 6 straight off the bat and perhaps somwhere like "United Bearing Company" at Coppell would be a good place to start.
http://www.unitedbearingcompany.com/...formation_.htm
Just walk up to the counter with the old bearings in hand and ask for two replacements, easy peasy!
Whatever you get after market just has to be better than the brass caged monstrosities you get as standard (and by the way this fact was confirmed by sole distributer here in Australia, he advised that new bearings would be a good idea if you are stripping the engine apart.)
http://www.unitedbearingcompany.com/...formation_.htm
Just walk up to the counter with the old bearings in hand and ask for two replacements, easy peasy!
Whatever you get after market just has to be better than the brass caged monstrosities you get as standard (and by the way this fact was confirmed by sole distributer here in Australia, he advised that new bearings would be a good idea if you are stripping the engine apart.)
02-17-2011 | 03:06 PM
#16
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RE: MARZ 2.5
Dang, my local bearing supplier is big, but not that big. Consider yourself lucky. I just found out that Ebay is a great place for bearings, but not in the hobby section, look through the industrial section for the part numbers you need. I purchased 10 6002ZZ-C3 NSK for 15USD. Last time I bought them locally I paid almost $4 each. RC-bearings wants $5.39 and Boca 8.99 plus shipping.
I looked through the manual for the Marz, but it doesn't list bearing sizes. If the sketch is accurate the front should be 6x15x5 (619/6) and rear 7x19x6(607), both common sizes.
I looked through the manual for the Marz, but it doesn't list bearing sizes. If the sketch is accurate the front should be 6x15x5 (619/6) and rear 7x19x6(607), both common sizes.
02-19-2011 | 07:02 PM
#17
RE: MARZ 2.5
I tried a couple of the places, but they aren't doing walk ups. You have to open an account with them as a business and order bearings ahead of time. Then someone from your business can pick them up at certain times. Of course I didn't try them all yet.
Thanks guys.
Thanks guys.
02-20-2011 | 01:31 PM
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RE: MARZ 2.5
ORIGINAL: earlwb
I tried a couple of the places, but they aren't doing walk ups. You have to open an account with them as a business and order bearings ahead of time. Then someone from your business can pick them up at certain times. Of course I didn't try them all yet.
Thanks guys.
I tried a couple of the places, but they aren't doing walk ups. You have to open an account with them as a business and order bearings ahead of time. Then someone from your business can pick them up at certain times. Of course I didn't try them all yet.
Thanks guys.
(Ifeel your pain when you say that a larger store couldn't be bothered with just two unknown bearing replacements worth less than $20 though!)
02-21-2011 | 07:43 AM
#20
RE: MARZ 2.5
ORIGINAL: Recycled Flyer
Ok then, just pull the crankshaft out, mic the bearings up and go to a smaller more user friendly store!
(Ifeel your pain when you say that a larger store couldn't be bothered with just two unknown bearing replacements worth less than $20 though!)
ORIGINAL: earlwb
I tried a couple of the places, but they aren't doing walk ups. You have to open an account with them as a business and order bearings ahead of time. Then someone from your business can pick them up at certain times. Of course I didn't try them all yet.
Thanks guys.
I tried a couple of the places, but they aren't doing walk ups. You have to open an account with them as a business and order bearings ahead of time. Then someone from your business can pick them up at certain times. Of course I didn't try them all yet.
Thanks guys.
(Ifeel your pain when you say that a larger store couldn't be bothered with just two unknown bearing replacements worth less than $20 though!)
Thanks
03-20-2011 | 04:32 AM
#21
RE: MARZ 2.5
I test ran one of my two MARZ 2.5 engines this weekend. It didn't take too long to get it to run. But after a few tanks of fuel, two of the head screws stripped out and fell out. On the last tank of fuel it was running pretty badly and surging like crazy, and had developed a need to turn in the compression screw more. That was when the head screws came out. I killed the engine and put the screws back in and then discovered that they had stripped out. I am hoping that I can drill them out for the next size up, which ought to be a 4/40 size SAE screw a they look like they have 3mm head screws. Hopefully whoever made the engine years ago, had done a poor job tapping the hole or they over torqued the screws down, and it isn't a poor alloy casting. Anyway that might help explain some of the messiness the engine exhibited when running. I thought it was just the oil oozing out around the exhaust collector ring.
The other Marz 2.5 engine had loose or bad bearings right out of the package. I haven't taken it apart yet to pull the bearings out so I can see what I can get to replace them with. But I'll have to check those head screws out again. I think on both engines I'll replace all the slotted screws with hex screws anyway. Those little slotted screws on the head aren't easy to loosen and tighten without tearing up the screw heads on them.
I also want to see about rotating that exhaust collector ring so that the exhaust output is not coming out right on top of the needle valve, as your hand gets all oily off the exhuast adjusting the needle.
I was getting almost 14,000 rpms using whatever that special Russian Prop is that came with the engine. Yeah I know real dangerous.
The other Marz 2.5 engine had loose or bad bearings right out of the package. I haven't taken it apart yet to pull the bearings out so I can see what I can get to replace them with. But I'll have to check those head screws out again. I think on both engines I'll replace all the slotted screws with hex screws anyway. Those little slotted screws on the head aren't easy to loosen and tighten without tearing up the screw heads on them.
I also want to see about rotating that exhaust collector ring so that the exhaust output is not coming out right on top of the needle valve, as your hand gets all oily off the exhuast adjusting the needle.
I was getting almost 14,000 rpms using whatever that special Russian Prop is that came with the engine. Yeah I know real dangerous.
03-20-2011 | 02:44 PM
#22
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From: SydneyNew South wales, AUSTRALIA
RE: MARZ 2.5
ORIGINAL: earlwb
I test ran one of my two MARZ 2.5 engines this weekend. It didn't take too long to get it to run. But after a few tanks of fuel, two of the head screws stripped out and fell out. On the last tank of fuel it was running pretty badly and surging like crazy, and had developed a need to turn in the compression screw more. That was when the head screws came out. I killed the engine and put the screws back in and then discovered that they had stripped out. I am hoping that I can drill them out for the next size up, which ought to be a 4/40 size SAE screw a they look like they have 3mm head screws. Hopefully whoever made the engine years ago, had done a poor job tapping the hole or they over torqued the screws down, and it isn't a poor alloy casting. Anyway that might help explain some of the messiness the engine exhibited when running. I thought it was just the oil oozing out around the exhaust collector ring.
The other Marz 2.5 engine had loose or bad bearings right out of the package. I haven't taken it apart yet to pull the bearings out so I can see what I can get to replace them with. But I'll have to check those head screws out again. I think on both engines I'll replace all the slotted screws with hex screws anyway. Those little slotted screws on the head aren't easy to loosen and tighten without tearing up the screw heads on them.
I also want to see about rotating that exhaust collector ring so that the exhaust output is not coming out right on top of the needle valve, as your hand gets all oily off the exhuast adjusting the needle.
I was getting almost 14,000 rpms using whatever that special Russian Prop is that came with the engine. Yeah I know real dangerous.
I test ran one of my two MARZ 2.5 engines this weekend. It didn't take too long to get it to run. But after a few tanks of fuel, two of the head screws stripped out and fell out. On the last tank of fuel it was running pretty badly and surging like crazy, and had developed a need to turn in the compression screw more. That was when the head screws came out. I killed the engine and put the screws back in and then discovered that they had stripped out. I am hoping that I can drill them out for the next size up, which ought to be a 4/40 size SAE screw a they look like they have 3mm head screws. Hopefully whoever made the engine years ago, had done a poor job tapping the hole or they over torqued the screws down, and it isn't a poor alloy casting. Anyway that might help explain some of the messiness the engine exhibited when running. I thought it was just the oil oozing out around the exhaust collector ring.
The other Marz 2.5 engine had loose or bad bearings right out of the package. I haven't taken it apart yet to pull the bearings out so I can see what I can get to replace them with. But I'll have to check those head screws out again. I think on both engines I'll replace all the slotted screws with hex screws anyway. Those little slotted screws on the head aren't easy to loosen and tighten without tearing up the screw heads on them.
I also want to see about rotating that exhaust collector ring so that the exhaust output is not coming out right on top of the needle valve, as your hand gets all oily off the exhuast adjusting the needle.
I was getting almost 14,000 rpms using whatever that special Russian Prop is that came with the engine. Yeah I know real dangerous.
And yes by all means use 4-40 hex head bolts but beware that the outer diameter of the bolt head is too large to fit down the holes in the fins so simply turn the head down a fraction. This beats the heck out of drilling the fins out!
Oh and as I have replied the same in another thread, use longer bolts and tap the hole right through to gain a far better grip in the casing.
Cheers.
03-20-2011 | 03:30 PM
#23
RE: MARZ 2.5
ORIGINAL: earlwb
...I also want to see about rotating that exhaust collector ring so that the exhaust output is not coming out right on top of the needle valve, as your hand gets all oily off the exhuast adjusting the needle...
...I also want to see about rotating that exhaust collector ring so that the exhaust output is not coming out right on top of the needle valve, as your hand gets all oily off the exhuast adjusting the needle...
The MARZ was available with and without an exhaust collector. I'm wondering if yours had the shorter screws for the no-collector version.
Good luck with it.
George
03-20-2011 | 03:41 PM
#24
RE: MARZ 2.5
You can tap M3 in 4-40 size holes but not the other way around (M3 is bigger than 4-40), thats what I do for stripped K&B .21 threads. If you want to stay SAE, 6-32 would be better!
03-20-2011 | 04:13 PM
#25
RE: MARZ 2.5
Thanks,
I was thinking 6-32, but I haven't messed with it yet to find out for sure. Usually if a metric screw strips out on me, I go with a SAE screw and tap to fix it as its the next size up slightly. So its metric to SAE and then metric if it strips out again or vice versa if its a SAE that strips out, I can go one slight size larger as a metric screw.
The screw holes in the head are small, so I might have to enlarge the holes to get the new screws to clear.
Interesting thought on the muffler ring and short screws. But the screws did extend about 1/32 of a inch below where they thread in at.
I suspect someone screwed up the tapping of the holes when the engine was made. Its hard to over torque a slotted screw like they used.
I was thinking 6-32, but I haven't messed with it yet to find out for sure. Usually if a metric screw strips out on me, I go with a SAE screw and tap to fix it as its the next size up slightly. So its metric to SAE and then metric if it strips out again or vice versa if its a SAE that strips out, I can go one slight size larger as a metric screw.
The screw holes in the head are small, so I might have to enlarge the holes to get the new screws to clear.
Interesting thought on the muffler ring and short screws. But the screws did extend about 1/32 of a inch below where they thread in at.
I suspect someone screwed up the tapping of the holes when the engine was made. Its hard to over torque a slotted screw like they used.
