650 case bike will 750 barrels fit?

Can I swap a set of 650 jugs and pistons for a 750? I mean if I am going to get a replacement set of jugs for a 1981-82 XJ Maxim 650, why not swap in a set of 750's. Anyone know if that swap will work without machine shop expertise? Will the 650 cyl head bolt up ok? Or would a 750 cyl head be needed?

Mike....

 

From my understanding the head is the same, same valves etc. cams are different .... 750 has longer duration for more top end power...
You would have to measure the outside of the liners to see if they are wider at the bottom...
750 has a longer stroke , so my guess is it wouldn't be a straight swap...
Someone else may know better than me, cuz I'm just speculating.
Alan

 

The 750 has a longer stroke. It can be done, but it's not just a straightforward piston and barrel swap. You'll also need to pay attention to whether your engine is a YICS engine or not. All XJ750 models are YICS engines, and you cannot mix/match YICS and non-YICS cylinders or heads.

If you just do a piston/cylinder swap you won't end up with 750cc because of the reduced stroke of the 650.

You'll also need to rejet your carbs to suit.

 

Wouldn't the crankshaft and cams have to support the swap?

Gary H.

 

Seems that there would be some serious compression ratio issues due to the longer stroke of the 750 with the shorter stroke of the 650. A total engine swap with carbs would probably be simpler.

 

It would. The mill would already be engineered to make the necessary hp.

Gary H.

 

Decent engines can be found on evilBay or at a wrecker for not too much coin, if yer lucky! Or a parts bike! Yaay! More XJs for everyone!!

 

My 650 is a yics. If the piston pin height were moved, the 750 could have the same rod length centre to centre. Therefore the connecting rods could be the same... Depends on the engineers at Yamaha if they did the piston height changes.

But aside from the swap parts stuff. is there any problems swapping a 750 engine for the 650? same frames?? any other changes? Other than tuning carbs....

 

Well Today there are only two engines of Yamaha XJ to be found on ebay (actually more but badly broken and overpriced for the condition.). Most bike wreckers are now dismantling them to sell in peices so as to make maximum return on investments

 

It would just be simpler to swap the entire engine.... Piston pin height.... And the bore is 2mm larger on a 750...
If it were 1mm larger ( like I thought it was) I was thinking you could use .040 over 650 pistons...
Not really an easy modification

 

Digging into an engine and ordering custom pistons is going to be way more expensive than finding a parts bike with a good engine. Too many times people have these bikes sitting around because they sat for too long and they are broke and can't fix them. Keep looking one will pop up sooner than later.

 

I am bidding on a 750 as i Type this..... non runner, but I think re ring and valve job is all that is needed. He wants 800 CDN, but I am going to offer 300. I also really dislike the looks of the square headlight and instruments, so I will have to figure in a set of 650 instruments and headlight. Anyone know if the 750 is a electronic tach as the 650 is?

 

83 750 maxim and seca is electronic


here is a link you can use to compare parts
http://www.yamahapartsnation.com/oemparts/c/yamaha_motorcycle/parts

if the part number is the same from any other bike as your bike it will fit your bike.
when you get to the part number click on it and it will list all the bikes it will fit

http://www.yamahapartsnation.com/oemparts/a/yam/5004203df8700209bc786dde/meter

click on part number in this link and it shows 81 82 83 seca have same tach
if you look up an 83 750 maxim you will see it fits both 650 and 750 for that part number

 

Just swap engines. Read the information overload hour for the swap details.

750 tach is electrical, 1980-1981 xj65maxim tachs were mechanical, 1982-1983 xj650maxim tachs were electrical

 

+1.

Gary H.

 

Cant find anything of use on this website regarding search functions. In fact I have never found a forum of any type with usefull search functions. I have better luck going outside the forums and running google search to search forums. lol so I will assume a swap to a 750 engine in a 650 frame would be of no consequence.

 

It has been done before but there is something different about the shifter and a few other things.

Think it would be best to have both bikes side by side to do a comparison before you start surgury.

 

Did you find the Information Overload Hour as hogfiddles suggested? It covers engine swaps. If you use IE, then Edit / find on this page / Engine Swaps will take you right to the applicable content.

http://www.xjbikes.com/forums/threads/the-information-overload-hour.27544/

 

Here ya go:

A little info from Chacal check out his information overload hour thread herehttp://xjbikes.com/Forums/viewtopic/t=27544.html


- ENGINE SWAPS:


XJ650 models:

Since one of the most popular engine swaps is putting an XJ750 engine into an XJ650 frame, we offer the following tips and guidelines regarding what issues you might expect to have to deal with in regards to this popular conversion. Also note that XJ750 Maxim/Midnight Maxim engines mount differently than XJ750 Seca engines, due to the lack of the rubber engine mounting insulators on XJ750 Seca crankcases.

* when putting an XJ700 (air-cooled) engine into a XJ650 Maxim, Midnight Maxim, or RJ Seca frame, please observe the following changes:

- observe the same procedures and cautions as applies to using the XJ750 Maxim/Midnight Maxim engines. The air-cooled XJ700 engines use rubber insulators to mount them to the frame, but you will need to retain the XJ650 engine mounting hardware (XJ700 engine mounts are in a different relative position in the frame).
- it is unknown which airbox boots you will need to use.
- the XJ650 Maxim/Midnight Maxim use the same style shifter assembly as an XJ700 engine, but differ from the XJ650RJ Seca shifter assembly.
- have to convert tachometer to an electrically driven version on all 1980-81 XJ650 Maxim, Midnight Maxim, and 1982 XJ650RJ Seca models.
- the XJ700 oil level sender can be used.
- will need to use XJ700 carbs and intake manifolds.
- need to retain XJ650 exhaust system.
- need to retain XJ650 wiring harness, except for the pick-up coils sub-harness. The pick-up coils on the XJ700 engines are different. Need to use the XJ700 TCI box.
- when using an XJ700 engine, be aware that there is a slight gearing difference----the XJ700 models have a slightly different gear ratio, also, even though they share the same size rear wheel as the Maxim. Thus there will be a difference in the acceleration of the bike, depending on which donor engine is used.
* it would be advisable to use the XJ700 swingarm assembly and driveshaft.
* one note of interest: the XJ700 engines, although of the same basic design as the XJ650 and XJ750 engines, are actually a much more "heavy-duty" unit, employing some of the XJ650 Turbo and XJ900 internal engine refinements and upgrades, as well as using a stronger, 6-spring clutch system, and also a much larger and stronger u-joint and driveshaft.


* when putting an XJ750 engine into a 1980-81 XJ650 Maxim or Midnight Maxim frame, please observe the following changes:

- have to convert tachometer to an electrically driven version.
- the original XJ650 oil level sender needs to be retained (unless the engine is from a 1983 750 Maxim or Midnight Maxim).
- the 650 shifter side cover and all internal components needs to be retained, unless you want to keep the 750 Seca style shifter. The 750 Maxim style shifter may not work.
- the engine mounting hardware for the XJ750 engine will need to be used (no rubbers on XJ750 Seca; XJ750 Maxim used the same basic hardware. Use the XJ650 front upper frame brackets when using a Maxim engine; the XJ750 Seca frame brackets when using a Seca engine).
- will need to use XJ650 airbox boots.
- will need to use XJ750 carbs (or re-establish the XJ650 carbs to XJ750 specs).
- need to retain XJ650 exhaust system.
- need to retain XJ650 wiring harness, except for the pick-up coils sub-harness. The pick-up coils on the XJ750 engines are different. Need to use the XJ750 TCI box.
- when using an XJ750 engine, be aware that there is a slight gearing difference----the XJ750 Seca used a 18" rear wheel, while the XJ650 Maxim models used only a 16" rear wheel, and thus middle drive gear ratios are slightly different inside the tranny. The XJ750 Maxim models have a slightly different gear ratio, also, even though they share the same size rear wheel as the Maxim. Thus there will be a difference in the acceleration of the bike, depending on which donor engine is used.


* when putting an XJ750 engine into a1982-83 650 Maxim frame, please observe the following changes:

- the original XJ650 oil level sender needs to be retained (unless the engine is from a 1983 750 Maxim or Midnight Maxim).
- the 650 shifter side cover and all internal components needs to be retained, unless you want to keep the 750 Seca style shifter. The 750 Maxim style shifter may not work.
- the engine mounting hardware for the XJ750 engine will need to be used (no rubbers on XJ750 Seca; XJ750 Maxim used the same basic hardware. Use the XJ650 front upper frame brackets when using a Maxim engine; the XJ750 Seca frame brackets when using a Seca engine).
- will need to use XJ650 airbox boots.
- will need to use XJ750 carbs (or re-establish the XJ650 carbs to XJ750 specs).
- need to retain XJ650 exhaust system.
- need to retain XJ650 wiring harness.
- when using an XJ750 engine, be aware that there is a slight gearing difference----the XJ750 Seca used a 18" rear wheel, while the XJ650 Maxim models used only a 16" rear wheel, and thus middle drive gear ratios are slightly different inside the tranny. The XJ750 Maxim models have a slightly different gear ratio, also, even though they share the same size rear wheel as the Maxim. Thus there will be a difference in the acceleration of the bike, depending on which donor engine is used.


* when putting an XJ750 engine into a 1982 650RJ Seca frame, please observe the following changes:

- have to convert tachometer to an electrically driven version.
- the original XJ650RJ oil level sender needs to be retained (unless the engine is from a 1983 750 Maxim or Midnight Maxim)
- the 650RJ shifter side cover and all internal components are the same as those in a XJ750 Seca engine. The 750 Maxim style shifter may not work.
- all engine mounting hardware for the XJ750 Maxim engine will need to be used (no rubbers on Seca engines; an XJ750 Seca engine uses the same mounting hardware as the XJ650RJ Seca, except for the front upper frame brackets, the XJ650RJ Seca frame brackets should be used. If using an XJ750 Maxim engine, you'll need to be creative.............
- will need to use the XJ650 airbox boots.
- will need to use XJ750 carbs (or re-establish the XJ650 carbs to XJ750 specs).
- need to retain the XJ650RJ exhaust system
- need to retain the XJ650RJ wiring harness, except for the pick-up coils sub-harness. The pick-up coils on the XJ750 engines are different. Need to use the 750 TCI box.
- when using an XJ750 engine, be aware that there is a slight gearing difference----while both the XJ650RJ Seca and the XJ750 Seca models used a 18" rear wheel, the XJ750 Maxim models used only a 16" rear wheel, and thus the middle drive gear ratios are slightly different inside the tranny on some engines. Thus there will be a difference in the acceleration of the bike, depending on which donor engine is used.


* when putting an XJ900 engine into a XJ650 Maxim, Midnight Maxim, or RJ Seca frame, please observe the following changes:

- although there are anecdotal stories of this swap being accomplished, we've never seen or verified the completion of such a project. There may be some engineering challenges involved due to the greater height of the XJ900 engines, as well as other issues.

Besides that, the same guidelines as generally outlined in the XJ700 engine swap should be observed.


* when putting an XJ1100 engine into a XJ650 Maxim, Midnight Maxim, or RJ Seca frame, please observe the following changes:

- put down the tools and the torch and back s-l-o-w-l-y away from the bike.
- 1100 engines are vastly different than the other XJ650/700/750/900 engines in design, style, size, etc., and attempting to put one of these engines into the smaller frames is likely to be a complete custom job. No other information is available. It would be wise to consider buying an XJ1100 model bike, and riding that, rather than trying to transplant just the engine.....


XJ700 air-cooled models:

Most of the engine-swap modifications in regards to the XJ650 engines above will apply, and recall that the XJ700 engines are rubber-mounted. However, due to the unique frame style and engine mounting positioning, you will need to use the XJ700 frame mounting brackets and hardware.

Please note that we have not attempted such a swap, and welcome further experience from those who have completed such as transplant for any additional insights.


XJ700 or XJ750 water-cooled models:

Although it should be possible to put an XJ-series air-cooled engine into the water-cooled frame, there will be many significant engineering challenges involved, as the XJ700-X and XJ750-X frames are unique enough that many difficulties will present themselves.


1981-83 XJ750 air-cooled models:

Most of the same consideration would apply as outlined in the XJ650 Section, just reversed. With the exception of the engine-mounting issues (rubber mounts on Maxim models, solid mounts on Seca models), all XJ750 air-cooled engines are basically identical to each other.


XJ750RL and XJ900 models:

No information is available on using the smaller XJ650/700/750 engines in the XJ750RL or 900 frame, although theoretically it should work.

Of course, XJ550 and XJ1100 engines will not fit into the XJ750RL or XJ900 frames without extensive efforts and modifications.

 

Thanks for the links. I found that thread on google....lol

 

I just looked it up through our own search engine right here on Xjbikes

 

Use Google. Type in your keyword(s) followed by a space and the command site:xjbikes.com That will limit the search to this site.

The search fearture in this forum software is almost as good as google.