Engine Swap: How to Put an X Engine into a 650 Seca Frame

A couple people have expressed interest in Rocinante, my "Seca X" bike, so I thought I'd start a thread about the trials and tribulations of putting an X engine into a 650 Seca frame. I'll start out with a bit of history about how the project came to be, then go into the technical details. It'll probably take several posts to cover it all - I'll start general then get as specific as people want to hear. Feel free to ask questions along the way.

I bought my 82 XJ650RJ near-new in 1985. Put a lot of miles on it those first few years, as it was my only vehicle and I had a long daily commute to university.
A few years later (1989 +/-) I was considering trading it in for something with a little more power, even though I loved the bike and the riding position fit me perfectly. One day I was in my local Yamaha shop looking at a used Maxim X. Started BS'ing with the salesman about how great the engine was but the cruiser styling wasn't to my taste, and wouldn't it be great to stick the X engine into my Seca? He gave me a funny look and said as a matter of fact, they had an X engine in the basement - an out-of-province rider had crashed his bike, his insurance company paid him out but never bothered to collect the bike. The engine was literally being used to hold the basement door open and most of the other parts were there too - no frame, but boxes of parts they had stripped off including the wiring harness and all the electronic pieces.

Following lots of measuring and head scratching (not enough measuring, as it turned out), we made a deal and I was off.

With the help of a friend who was a much better mechanic than me, the engine went in and the bike was in rideable (but not pretty) condition within a couple weeks. Fine tuning and improvements have been going on in fits and starts ever since - 24 years later the project still isn't what I'd call finished. It has been ridden regularly that whole time and I don't see that stopping any time soon.

So, to start with the FAQ's:
1. Is it possible to put an X engine into a Seca frame? Yes.
2. Is it a quick and easy swap? No.
3. Is it worth it? That depends

Longer answer to No. 3: if you like your 650 Seca (or Maxim) but want more power, a far quicker, easier, and probably cheaper route would be to sell the 650 and buy a 900. You won't be disappointed. But if you have access to a complete X engine in good condition and you want something a bit unique, Rocinante is living proof that it is possible. One warning is that if you spend a lot of time in stop-and-go traffic in a hot climate, be prepared for some significant challenges in getting the cooling system to work as effectively as on the stock bike due to frame differences.

The project has it's share of challenges but doesn't require any frame surgery or special fabrications. Some of the challenges are obvious (like, how the heck am I going to mount that radiator and run all the cooling system plumbing?) and some sneak up on you but they are all fixable, and overall the swap is a piece of cake compared to some of the builds that people have shared on this forum.

Tomorrow I'll start with the technical details.

 

I'd like to see more about that mod. I've owned an X for a few years and sold it 3-4 years ago, then I just bought a Seca900 this winter, so I won't be makng this mod myself, just curious how much work it is to fit the cooling system and so.

 

Sorry for the mini-hijack, I've got "Cygnus X-1" stuck on the brain now... 8)

Quite appropriate bearing in mind your location as well. Perhaps you should consider calling the conversion a "Seca X-1" as it's probably the first of it's kind & will get you to your destination in a Rush compared to stock? :wink:

 

Re: Engine Swap: How to Put an X Engine into a 650 Seca Fra

Today's episode: the swap.

If you are planning to do an engine swap of any kind, the first thing to do is read the "Engine Swaps" section of Chacal's Information Overload Hour. Lots of good info there, even if he doesn't mention putting an X engine into an airhead frame.

The second thing to do is get as many parts from the donor bike as you can. Obviously you will want things like the TCI unit, the temperature gauge, and the spark plug caps but there will be others as well. I happened to get the wiring harness from the X bike and even though I didn't use it, it was useful to be able to scavenge connectors for things that the airhead doesn't have - like temp gauge, fan, and electric tach. Not to mention the odd connector or component that is just different because it is a different year and model. Sorry, I can't remember all those details but they aren't difficult to figure out as you go along.

But don't give away your airhead engine and parts too quickly. You will be doing a lot of 'mix and match' before you are done.

Fitting the engine into the frame is the easiest part. The engine mounts line right up. Note that the X engine uses rubber mounts and Secas use solid mounts. The mounts cast into the crankcase are actually identical, it is just the bushings that are different. So you can decide if you want to keep the solid mounts, for maximum rigidity, or the rubber mounts, for comfort. I chose to use the rubber mounts. You might have to trim some frame tabs if you are going from solid to rubber mounts.

The X engine is a little taller, but the good news is that it goes in without having to do anything more drastic than removing the oil filter housing. The X frame has a removable section but I'm not sure why. Probably makes engine removal easier but isn't strictly necessary.

Once in the frame, all of the normal maintenance things are just as accessible as on the airhead except that the you have to remove the upper coolant hoses, thermostat housing, and coils and then use some strong language to get the valve cover off to do a valve adjustment. It does come off without loosening the frame bolts, but just barely. I think you could take the head off without removing the engine from the frame but I've never tried.

I remember my friend and I struggling to get the engine in the frame and the clearances were tight. Much later I read on this forum about laying the engine on its side, lowering the frame onto the engine, and then standing the whole thing up. Wish I'd known that at the time, I'm sure it would be a lot easier that way!

 

Re: Engine Swap: How to Put an X Engine into a 650 Seca Fra

Now is when it gets interesting: the cooling system

The cooling system is by far the hardest part to make fit, and I'm still not happy with it. I'm on Version 3.0 of the radiator and plumbing setup and it works reasonably well but Version 4.0 is in the planning stage.

Here's a diagram of the cooling system from the factory manual:



Item number 6 in the diagram is the thermostat housing. It also functions as a junction for the 2 pipes from the water jacket and the filler neck and includes tapped holes for the temperature sensor and fan thermo switch, making it an unwieldy shape with things coming out at all angles. It takes some shoehorning and relocations, but it is possible to fit it in the void space between the upper frame tubes, in front of the coils and behind the steering head. The key is the filler neck. I drilled a hole for it in the steering head gusset on the right side, just forward of the tank as shown in this picture:



The hole is at the geometric center of the gusset plate so the loss in structural rigidity is minimal. There is a short piece of copper pipe at the point where it goes through the gusset so that there isn't any rubber-on-metal rubbing that could wear through the hose. The outlet from the thermostat housing goes out underneath the steering head and into the top of the rad like so:



Yes, those are zip straps holding the top of the rad to the frame. Don't judge me. The bottom brackets take all the weight, the zip straps just hold the top of the rad back against some little rubber pads between the rad and the frame. I experimented with several ways to do this and the zip straps have just the right combination of strength and flexibility, plus they conform to the angles of the frame tubes and don't require any drilling or welding. I carry spares with me and check them regularly but have never had any problem.

The rad itself is custom made with more volume and surface area than the stock rad. This is to compensate for the fact that there is no room for the stock fan, or any other decent fan that I can find. The frame on the X has the front frame tubes splayed apart to make room for the fan - other XJs don't.

Not much room for a fan in here:



The next (hopefully final) version of this setup will have the cooling pipes running around the left side of the engine instead of over the top. That will allow me to mount the rad a bit higher. And then hopefully I can find a fan which is large diameter but thin and mount it in front of the frame. Of course then I would also need to find or fabricate a new, simpler thermostat housing, get rid of the filler spout altogether and put a filler cap on the rad itself. That will most likely be a next winter project.

Suggestions for improvement are welcome!

 

Cool! The thermostat housing was certainly one of the things I hated the most on my X (second is the water pump setup). Its location and configuration were really ackward.

You have an inventive mind, keep on using it!

 

Merci, Monsieur Quebecois!

Getting that thermostat housing to work was definitely a struggle. Cost me some skin off my knuckles too!

 

Re: Engine Swap: How to Put an X Engine into a 650 Seca Fra

Today's episode: Miscellaneous "Gotchas"

Here's a detail that seems small (and which I missed completely when I was measuring up the engine) but has some semi-serious implications: the carbs are about an inch further back compared to other XJs. This is because the water pump sits behind the #4 cylinder and the intake boots are longer so that the carbs clear the water pump.
This has 2 implications:
1. Top of carb hits the tank. Relatively easy fix if you don't mind doing a bit of bodywork on the tank. The bodywork is on the underside of the tank so it doesn't change the overall lines.
2. Stock airbox will not fit. The carbs hit the airbox with no room at all for intake rubbers. I cut off the front part of the airbox and left the back part in place and put the coolant overflow tank inside it. Here are a couple pictures, one with the sidecover on and one with it off:





To make matters worse, the #1 and #4 carb intakes point right at the frame tubes which limits your options further. Foam Uni filters work (as I have used) but rigid ones like K&N or Emgo don't fit.

Replacing the battery with a lithium one and fabricating a custom airbox and intakes is on the 'things to do' list. But in the meantime it runs fine with the pods. Could probably be a bit better with an airbox, though.

Another 'gotcha' that looks serious but turns out to be an easy fix, is the gearshift lever. The Maxims have a lever that points forward to suit the forward foot position; Secas have a rearward-pointing lever with a linkage to suit their footpegs which are further back. Fortunately, you can just swap the whole shifter cover and shifter assembly - it all comes together in one neat package.

The 650 Seca driveshaft and U-joint bolted right up to the output flange on the X engine. However the X driveshaft and U-joint are substantially beefier so you'll want to use that if possible. I would have liked to but when I tried to fit it I found that the X driveshaft is a bit too long so the Seca shaft is still in there. Another item for the 'to do' list: either get the X shaft shortened at a machine shop or find some combination of parts from another XJ (maybe a Turbo?) that fits.

So there you have it - the ongoing Seca X project. More of an evolution than a project, though. It's been my regular rider since 1985 with only a few interruptions when things like mortgages got in the way. Riding has always been my priority, as opposed to wrenching, but I was glad that this past winter I had the time and the space to tackle some cosmetic issues that I'd been wanting to get around to (not to mention catch up on the maintenance and do the first-ever carb rebuild). It may never be "finished" but I insured it this past weekend so it's back in 'riding' mode now for the next 6 months (and it's running GREAT, thanks for asking!).

Feel free to ask me anything if you want to try this yourself, or are just curious about anything I might have skipped over.

 

Re: Engine Swap: How to Put an X Engine into a 650 Seca Fra

I had those same filters with my round slide carbs and had the same problem with room for them because of the 2 into 1 intakes that I made. Because they were scrunched up, they came apart after awhile. So I got a couple of rubber plumbing couplings from the carbs to some pvc elbows going into a tee and then attached the filters. They are tucked under the seat, but there was still room for the battery.

 

IS it just me or you had to cut and reshape your side covers a bit too?

 

Orange-n-Black - I just read your build thread - all 12 pages! - and the intake you made is impressive. I'm thinking of something similar to the PVC setup you had when you still had 4 carbs except I'm going to try using 45 degree bends rather than 90's. And then run the 4 intakes into a box of some sort, either fiberglass or plastic, with a single large pod air filter pointing down. Ideally I'd also like to do the lithium battery and mount it up high to get that open-under-the seat look.

Quebecois - yes you are right, I trimmed the side covers to match up to the 5Valve chrome piece. Thought about trimming them back even further to expose the pods but realized that I would get filter oil on my pant leg all the time.

 

Excellent job explaining issues. This thread will definitely come in handy come winter when I attempt to make a midnight maxim X. I'm sure I'll have plenty of questions for ya then.

 

Re: Engine Swap: How to Put an X Engine into a 650 Seca Fra

Quixote wrote:
Quixote
PostPosted: Wed May 01, 2013 9:14 pm Post subject: Re: Engine Swap: How to Put an X Engine into a 650 Seca Frame
Orange-n-Black - I just read your build thread - all 12 pages! - and the intake you made is impressive. I'm thinking of something similar to the PVC setup you had when you still had 4 carbs except I'm going to try using 45 degree bends rather than 90's. And then run the 4 intakes into a box of some sort, either fiberglass or plastic, with a single large pod air filter pointing down. Ideally I'd also like to do the lithium battery and mount it up high to get that open-under-the seat look.

I installed that pvc setup on my son-in-laws bike recently and it didn't work well. Don't know if it was the positioning of the filters, too many filters or the rubber couplings aren't long enough. The couplings also have a step design that may have caused turbulence. It seems that most pvc setups that have worked, had one filter and straight, long couplings.

 

Good to know. I'll keep that in mind when I'm designing mine. Thanks for the tips.

 

Cool project, bet she screams pretty good!

 

Is that a Mac 4-1 exhaust and is it actually for the maxim x or from your seca. Haven't been able to find an ALL black exhaust for the X yet...just black with chrome muffler

 

The header pipes are from a Laser system designed for the Seca. The Laser canister looked cheesy and the packing wore out quickly (non replaceable) so I replaced it with a Supertrapp which is much better. So what you are seeing is Laser headers for the Seca plus a slip-on Supertrapp.
On this build, I found that neither the stock Seca headers nor the X headers fit properly due to slightly different forward lean on the cylinders. The Laser headers were 'persuaded' to fit by putting them individually into a vise and tightening up the bend by a few degrees. Worked OK on these particular pipes but I don't think you could do that on a double-walled pipe. Still kept the centerstand and access to the oil drain, which is a good thing.

Thanks for bringing that up - I should have listed that issue in the 'gotchas'.

Laser does still make a 4:1 for at least some XJ models but apparently only in chrome, not black.

 

Thanks that's a big help. I'm wanting new exhaust because my header pipes are a bit rusty and the one is smashed a bit from the PO bottoming out on something. Also has an ugly chrome Jardine muffler on it that sounds good but looks gaudy against all the black on my bike. Since I decided I'm going to do this swap this winter I wasn't sure which exhaust to get (maxim x or midnight). I was aware of the different lean angle of the top end so I didn't think the exhaust for my midnight would fit after the swap. However seeing that you made your seca headers fit I think I'll just go ahead and get the exhaust for my midnight and just make it fit the x motor when I do the swap this winter.

 

Yeah, it was definitely easier to fit the Seca pipes than the Maxim X ones in my case. I don't remember exactly what the problem was with the X pipes but I remember holding them up and figuring out pretty quickly that they wouldn't fit. Of course if you have both systems you'll probably be doing the same thing - holding each set up in place and seeing how the mounts line up, etc. Then you can easily judge whether it's feasible to make it fit.
Of course if budget allows you could always get some custom headers made up and powder coated, then get a carbon fibre slip on - that would look good and drop a lot of weight.

 

Awesome job man!