Displacement / horse power increase - swappable parts

Quimrider · 11-14-2008, 04:53 PM

To avoid any confusion with this topic:Convert your GZ250 into a 346cc!!! THERE IS NO BIG BORE KIT FOR THE GZ250. ALSO TO ABOUT 99.999999991% OF THE POPULATION THE COST THAT WOULD BE INVOLVED IN COMING UP WITH YOUR OWN BIG BORE KIT DOES NOT MAKE SENSE. If you would like to discuss the nonexistence of a big bore kit or the fact that modifying the engine is too expensive, please do so in the thread above.

This thread is to discuss which engine parts are/are not interchangeable with the GZ250's engine and various methods one could do to increase displacement and/or horsepower. Additionally I'd like to entertain the topic of potential engine swaps as a means to get more juice out of the GZ250. For example I have read about a Honda Rebel that had a diesel engine shoe horned onto it.

Please minimize speculation/opinion and stick as close as possible to the facts.

One engine of interest is that from the DR350. It is very similar to the GZ250 engine. The DR350 has a 79mm X 71.2mm bore and stroke. The GZ250 engine is 72mm x 61.2mm bore and stroke. Aside from custom exhaust work, the main obstacle from simply swapping the top half of the engines is that the DR350 engine has a 10mm longer stroke. If I ever get my hands on a DR350 cheap enuff I will attempt to put the DR350 engine on the GZ250.

perroloco · 11-16-2008, 04:12 PM

It should be a big bore kit or something ,I own a Baja 300 extreme ATV made for pep boy with a 300cc head on the same eng that I have on my gz250, the head is identical to the 250 but is 296cc, when I by parts for it, I use the 250 parts catalog

Sarris · 11-16-2008, 10:11 PM

:jo: :banana: :jo: :banana: :jo: :banana: :jo: :banana: :jo: :banana: = Jerkin' the bananna.

Quimrider · 11-17-2008, 10:32 AM

LMAO

music man · 11-19-2008, 09:01 AM

hey Quimrider, here is an old beat up DR 350 engine, it probably wouldn't be cost effective either, but i figured I would show you anyways.

http://cgi.ebay.com/ebaymotors/SUZUKI-1 ... ccessories

Quimrider · 11-19-2008, 11:13 AM

Thanks, if I can get it cheap enuff I'll have to see what it would take to make it fit. I found the DR350 service manual, we'll see if there's any useful info in there. Worse case, I'm out a few bucks and some time to learn it won't fit.

**jonathan180iq** · 11-19-2008, 04:45 PM

If you can get a running engine for a $100 or so and are able to fabricate whatever motormounts would be needed to make it fit, then I think this might be a viable option for anyone with the dough. Otherwise, it's just $h1t polishing.

ruxpin76 · 03-12-2010, 01:37 PM

Kart racers swap and modify cylinders/head regularly for the open classes. The DR head might work IF the cylinder is the same height. (Unlikely.) To make a swap, you'd have to make sure: (1) The wrist pin on the piston is the same size as the GZ piston, (2) The cylinder was the same height, (3) the timing chain had clearance to still run the cam, (4) the studs lined up with the GZ pattern as well as gaskets. LA Sleeve makes custom sleeves, and since we're dealing with a 4 stroke, there's no custom porting IN the sleeve. It'd be pretty simple (but pricey) to have a custom billet unit made. To do so:

1. Get a piece of aluminum that's the right size.
2. Bore the cylinder stud holes with correct clearances
3. Bore the head stud holes, if head doesn't share studs with cylinder
4. Tap applicable holes.
5. Mill out timing chain hole
6. Mill out cylinder hole
7. Heat case, cool cylinder and mate the pair, including any retainer/locater, same as DR.
8. Test fit and check for any mechanical intereference
9. deburr, lube, reassable
10. Pray the extra power doesn't snap the GZ crank, which can be helped by:
11. Rebalancing the crank counterweights to match the heavier pistion by boring and adding tungsten weights
12. Start new spouse search because your old one divorced when you went bankrupt making a $3000 cylinder for a $3K bike.

Hope that helps....fun hobby project if you're a machinist (I am) or if you know one, but hardly cost effective.

Alternatively, you could use the DR rod on the GZ crank and use the stock DR cylinder if the lower rod bearing's the same size and all the other holes match up and the head/timing chain assy. has proper fit...

ruxpin76 · 03-12-2010, 06:17 PM

1980's DR250 has same bore/stroke...

Quimrider · 03-12-2010, 06:24 PM

Quote:

Originally Posted by ruxpin76

12. Start new spouse search because your old one divorced when you went bankrupt making a $3000 cylinder for a $3K bike.

:lol: how true how true.

11-14-2008, 04:53 PM	#1
Quimrider Senior Member Join Date: Jun 2007 Location: Toledo, OH Posts: 198	Displacement / horse power increase - swappable parts To avoid any confusion with this topic:Convert your GZ250 into a 346cc!!! THERE IS NO BIG BORE KIT FOR THE GZ250. ALSO TO ABOUT 99.999999991% OF THE POPULATION THE COST THAT WOULD BE INVOLVED IN COMING UP WITH YOUR OWN BIG BORE KIT DOES NOT MAKE SENSE. If you would like to discuss the nonexistence of a big bore kit or the fact that modifying the engine is too expensive, please do so in the thread above. This thread is to discuss which engine parts are/are not interchangeable with the GZ250's engine and various methods one could do to increase displacement and/or horsepower. Additionally I'd like to entertain the topic of potential engine swaps as a means to get more juice out of the GZ250. For example I have read about a Honda Rebel that had a diesel engine shoe horned onto it. Please minimize speculation/opinion and stick as close as possible to the facts. One engine of interest is that from the DR350. It is very similar to the GZ250 engine. The DR350 has a 79mm X 71.2mm bore and stroke. The GZ250 engine is 72mm x 61.2mm bore and stroke. Aside from custom exhaust work, the main obstacle from simply swapping the top half of the engines is that the DR350 engine has a 10mm longer stroke. If I ever get my hands on a DR350 cheap enuff I will attempt to put the DR350 engine on the GZ250. Login or Register to Remove Ads
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11-16-2008, 04:12 PM	#2
perroloco Junior Member Join Date: Nov 2008 Location: miami Posts: 4	Re: Displacement / horse power increase - swappable parts It should be a big bore kit or something ,I own a Baja 300 extreme ATV made for pep boy with a 300cc head on the same eng that I have on my gz250, the head is identical to the 250 but is 296cc, when I by parts for it, I use the 250 parts catalog
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11-16-2008, 10:11 PM	#3
Sarris Senior Member Join Date: May 2007 Location: New Port Richey, Florida USA Posts: 1,348	Re: Displacement / horse power increase - swappable parts :jo: :banana: :jo: :banana: :jo: :banana: :jo: :banana: :jo: :banana: = Jerkin' the bananna. __________________ Prudent riders live longer than moron riders. Login or Register to Remove Ads
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11-17-2008, 10:32 AM	#4
Quimrider Senior Member Join Date: Jun 2007 Location: Toledo, OH Posts: 198	Re: Displacement / horse power increase - swappable parts LMAO
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11-19-2008, 09:01 AM	#5
music man Senior Member Join Date: Jun 2008 Location: Hot Springs Arkansas Posts: 1,127	Re: Displacement / horse power increase - swappable parts hey Quimrider, here is an old beat up DR 350 engine, it probably wouldn't be cost effective either, but i figured I would show you anyways. http://cgi.ebay.com/ebaymotors/SUZUKI-1 ... ccessories __________________ "Tell me what kind of wreck you're going to have and I'll tell you what type of helmet you need." [Author Unknown] Login or Register to Remove Ads
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11-19-2008, 11:13 AM	#6
Quimrider Senior Member Join Date: Jun 2007 Location: Toledo, OH Posts: 198	Re: Displacement / horse power increase - swappable parts Thanks, if I can get it cheap enuff I'll have to see what it would take to make it fit. I found the DR350 service manual, we'll see if there's any useful info in there. Worse case, I'm out a few bucks and some time to learn it won't fit.
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11-19-2008, 04:45 PM	#7
jonathan180iq Super Moderator Join Date: Jan 2007 Location: Dalton, GA Posts: 3,996	Re: Displacement / horse power increase - swappable parts If you can get a running engine for a $100 or so and are able to fabricate whatever motormounts would be needed to make it fit, then I think this might be a viable option for anyone with the dough. Otherwise, it's just $h1t polishing.
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03-12-2010, 01:37 PM	#8
ruxpin76 Member Join Date: Mar 2010 Location: King, NC Posts: 59	Re: Displacement / horse power increase - swappable parts Kart racers swap and modify cylinders/head regularly for the open classes. The DR head might work IF the cylinder is the same height. (Unlikely.) To make a swap, you'd have to make sure: (1) The wrist pin on the piston is the same size as the GZ piston, (2) The cylinder was the same height, (3) the timing chain had clearance to still run the cam, (4) the studs lined up with the GZ pattern as well as gaskets. LA Sleeve makes custom sleeves, and since we're dealing with a 4 stroke, there's no custom porting IN the sleeve. It'd be pretty simple (but pricey) to have a custom billet unit made. To do so: 1. Get a piece of aluminum that's the right size. 2. Bore the cylinder stud holes with correct clearances 3. Bore the head stud holes, if head doesn't share studs with cylinder 4. Tap applicable holes. 5. Mill out timing chain hole 6. Mill out cylinder hole 7. Heat case, cool cylinder and mate the pair, including any retainer/locater, same as DR. 8. Test fit and check for any mechanical intereference 9. deburr, lube, reassable 10. Pray the extra power doesn't snap the GZ crank, which can be helped by: 11. Rebalancing the crank counterweights to match the heavier pistion by boring and adding tungsten weights 12. Start new spouse search because your old one divorced when you went bankrupt making a $3000 cylinder for a $3K bike. Hope that helps....fun hobby project if you're a machinist (I am) or if you know one, but hardly cost effective. Alternatively, you could use the DR rod on the GZ crank and use the stock DR cylinder if the lower rod bearing's the same size and all the other holes match up and the head/timing chain assy. has proper fit...
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03-12-2010, 06:17 PM	#9
ruxpin76 Member Join Date: Mar 2010 Location: King, NC Posts: 59	Re: Displacement / horse power increase - swappable parts 1980's DR250 has same bore/stroke...
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