Jplecas Intro: maxim & seca

Hello! Im new to motorcycles so im glad ill be able to use this forum for help. Anyways, on with the pictures!



I got the maxim first, about a week ago. It has a bad motor but i only paid $140 for it. Not only does it have a rod jutting out of the case, but it also looks like the PO didnt think fuses were necessary.





But it did look like all of the parts were there, and i thought it would be a good base to start with. so i started looking for another engine or a donor bike, and ended up getting the seca a few days later.





I paid $200 for this one, and was planning to use the motor for the maxim. But once i was able to look the seca over, i realized it was in much better shape. The tires still have the nubbie things, and the brake rotors arent grooved to shit like the max. The PO said it ran, but was sluggish and wasnt very smooth. The guy he bought it from told him the carbs needed rebuilt. So i guess he took the carbs off and it sat for 9 months.

After I got it home, I took the carbs apart and noticed a couple things wrong. Ive never worked on carbs before so i dont know what anything in here does, but heres the issue.



You can see the pin im holding to the left. three of the carbs had the pin just like that, with no retainer spring on top. The 4th pin had a spring, and was a different style than the other 3. Also, the bolt thing that the pin slides into was shorter than the other 3.

I took the carbs out of the maxim and they all had the retainer spring. Also all of the bolts were the shorter style. what i did was swapped the pins from the maxim, into the seca carbs and buttoned everything up. I just wanted to see if i could get it running while im waiting for a rebuild kit for the carbs.

What does that pin do? could this have caused the bike to run poorly like the PO said?

Next problem, this one has me worried. it looks like he took the covers off of both sides of the engine, as they had new blue gasket material, and were missing some hardware. I think he did it to fix a leak because the bottom of the bike is pretty grimey. but I also realized it wouldnt shift. the spline rotates like normal, but nothing happens. it just freely goes back and forth. I figured he just didnt put some linkage back correctly so i pulled the cover off.



I tried shifting it from here and still, nothing happened. When i looked inside the inspection port, on the upper left side. I noticed something that didnt look normal. on top of the gear shaft there was a black thing moving around on top. i pulled it out and here it is...



So what the heck is that? Im now thinking that my shifting problem is internal, might i be able to swap parts from the maxim to get this one working properly?

Thanks everybody i really appreciate any help that can get me riding!
-Joseph

 

Oboy.

That is a piece of the "primary" chain guide. Yours has begun to break up, a common problem on the shaft drive XJs. Pieces will continue to break off now that it's begun to disintegrate. It's not a part you want to try to "swap" you need a NEW one. The one in the Maxim is just as likely to fail.

Replacing it requires splitting the cases. Splitting the cases, replacing the guide and getting the motor back together successfully requires a service manual, so it doesn't end up like the Maxim.

Oh, and in regard to tires: The existence of the "nubby things" means nothing. Tubeless tires more than 6 years old are dangerous. Check the date codes on the tires, not the amount of remaining tread.

 

First comment:

You should put the year/model/size/mileage of bike in your signature, that way I will be the only one who has to ask this...

Question:

Is the Maxim a 750? I am going to assume it is, since the Seca was purchased as a donor motor.

What years?

Two comments about the Maxim:
1. WOW! That's a HUGE hole
2. Ewwww....pods.

The Seca:

Looks like a very good base to start from. Personally, that's the one I would start with trying to recommission.

The "pin" you are holding with the pliers is a float needle, and yes, they are very important for the bike to run correctly. Actually, EVERY part in these carbs is important for the bike to run correctly.

The "black thing" on the other hand, I don't know what that is. I've not had that cover off yet.

These are the things you should do, and please don't skip ANY of these, or you will give yourself a headache from beating your head against the wall in frustration. But if you do it correctly, you will have one of the most fun bikes that will last many many more miles.

Get a manual
Compression test
Check/adjust valve shims (before syncing carbs)
Carbs: clean, bench sync, fuel height, running sync, tune. (replace all questionable parts)
Replace all filters and fluids
Replace plugs
Check rear brake for delamination
Bearings in the steering head, front wheel, and back wheel
Check front brake hose codes, replace if needed. The originals were only good for 2 years. (Go stainless)
Rebuild Master cylinder and caliper
Replace fuse box with modern blade style fuse panel
Check/rebuild petcock
Install inline fuel filter
Replace tires if more than 6 years old, cracked, or any other defects
Clean all electrical connections
New battery.

I'm sure I forgot a few.

It looks like a big list, but if you take your time, study the manual and especially the posts on here, and be thorough, it will be well worth the time and money.

Yes some parts will interchange with the Maxim, but someone with a 750 will have to chime in on that.

And don't be afraid to ask for help. If you put your location in your profile you might even have someone close that is willing to come help out.

WELCOME TO THE CLUB!

 

Okay im not familiar with the term split cases. What is involved in that? Like, what else am i going to have to replace since im opening the engine up? Splitting the cases to me sounds like an engine rebuild.

 

Yamaha parts fiche

Bookmark the parts fiche for future reference. We use it A LOT! LOL

Search for OEM parts - motorcycle - your year - XJ750R - crankcase

 

The crankcase on the XJ series is split horizontally. You need to separate the two crankcase halves to make the repair. It is "halfway" to a bottom end rebuild, except you won't be replacing main bearings or anything like that; it's the only way to access the chain guide. You will be separating the main bearings, etc., just not replacing any of that.

If you simply invert the motor and split the main crankcase halves to replace the chain guide, required parts (other than gaskets and the guide itself) are minimal. There is an oil nozzle in there that gets "attacked" by the chain that usually benefits from being replaced; that's about it.

However, it's a rather complex bit of surgery, requiring quite a bit of disassembly; and concentrated care especially during reassembly.

IT'S A PROCEDURE THAT REQUIRES A SERVICE MANUAL; factory book preferred. DO NOT attempt it without a book, you will likely irrepairably damage the motor.

 

If you decide to "Go-for-it", ...
Get organized.

Most importantly, ...
Acquire a FACTORY Manual.

The Factory Book will walk you through the Split and SHOW you where everything goes and exactly how it fits.

There are diagrams, like this one, which are most helpful in keeping the project organized and YOU less intimidated about doing the job.

When you get to the point where you unbolt the two halves, ... make 2 Cardboard cut-outs like this Diagram illustrates.
Use a ruler and a Sharpie.
Stab holes through the Cardboard keeping the Pattern precise.

As you remove a Bolt, ... place it where it belongs on the Cardboard Pattern.
You'll be assured of selecting the right fastener for each spot when you are buttoning the job up.

:::::::: YAMAHA Factory Workshop Manual Illustration ::::::::

 

Welcome to your new winter hobby/job! The plus side is you got two GREAT deals price wise on those bikes. Some parts on these bikes are worth as much or more than you payed. So relish your good deal and look at it as an adventure in learning, and eventually creating a really nice bike that you can brag about fixing! Once you figure out what you need to get one back to great you could sell what you don't need to recoup your costs and improve the one you do keep.

You'll notice that you will get advice from XJ'ers that have much experience with these machines (like the responses you already have on here) and if you get stuck or need help - you'll get it. I'd say if you decide to tackle what's needed - a clean workspace and clean parts is needed and staying organized is critical. Utilize a digital camera, notebook, metal tins, etc.

It would be great to see pictures and hear about the progress as you go along. Nice to see these classics get new life.

And that is one giant hole in that case! I'll bet when that happened the po either peed his pants or started praying if he was riding it at the time.

 

That maxim doesn't look to be a 750, but a 650, judging by the single disc brake in front and the handlebars. It's also looks to be pre-YICS, which would make it an '80 or '81. I don't know about the Seca.

 

On those bowl needle valves, make sure that ALL of them are identical. The little wire clip on the end of the valve needle fits over a tab on the float, it is this tab that you bend either up or down with small needle-nose pliers to adjust the fuel level in the bowl. There are other threads which can show you how to do various carb adjustments, just do a search.

 

One bike has a hole in the crankcase the size of a softball with a rod hanging out;

the other bike has a disintegrating primary chain guide.

I'm thinking float needle valve pins are not gonna be on the radar for a while...

 

Wade-a-minnit - -

First - Welcome to the Greatest Site for XJ's, Jplecas

OK, we recently had another #1 rod thrown by another member, and, there's a Youtube of a running XJ with the #1 rod thrown.

Is this the last place to get oil on the crank?? (pressure-wise?)

 

Think about it for a minute: how common is "gas in the crankcase" syndrome?

How many completely clueless fools fail to notice it when it happens? This is NOT a reference to the member who just blew up his Max, he admitted he'd run it out of oil over the summer due to a leak. It was wounded already.

XJs that blow the bottom end like that are a good illustration of what happens when you don't realize your oil has been diluted in half by gasoline and continue to run the motor at high speed. It's a plain bearing motor; it'll run just fine until it seizes tight and goes BANG! Or, KABLAMMO as David Hobbs says.

 

HAHA - a friend said "WANKEL" is the sound an RX-7 makes when it blows !!

But to my Q - doesn't the oil feed into a common galley from the pump, equally distributing the pressure to the Mains, then on to the Rods??

I find it curious that #1 let go 3X. But considering 10,000 members here, that's not too shabby !

 

For the sake of poor #1



If Yamaha is laying this out truthfully then it does appear that even though oil enters the main gallery centrally, it leaves the crankshaft on one side to feed up to the cams. This would create a pressure difference going across. That being true doesn't mean imminent failure, but a failing/failed pump is a different story (no oil). And oil that has thermally broken down (extreme heat) is not much better than no oil at all, maybe worse depending on what it's melting and how close to coal its become!

So bad oil, low oil, fuel oil, no oil=no good. Pre-ride checks are gooood.

Ha I just noticed that we have 1 set of lifters and 1 set of lefters in our XJ's! How come no righters?

 

Nice diagram - - I see the clutch and shifter don't drain back, and no mention of the Middle Gear cavity ??

 

LOL it was something like that.. :lol: The car has spent the last year in pieces, soon ill be able to start putting break in miles on it. I was hoping the Seca would be a quick fix but since its gonna be a bit of a project itself, im going to focus on getting the mazda finished up for now.

As far as the problem on the #1 cylinder with the maxim. I wouldnt mind taking that apart to look at the damage on the inside. if it was an oil problem im sure the bearings would have some serious burn marks.

 

Maybe this oil issue is just coincidental, maybe it's just a few machines got thru the factory without getting #1 rod cap being torqued, just tightened. It could hold for thousands of miles then let go as vibration caused the nuts to finally loosen and fall off. I say this because I don't think this damage is caused by a seized bearing; what I see happening is the cap comes loose and falls away, the piston stops it's travel and the rod just happens to gets wedged between the case and the still rotating crankshaft there by causing the great amount of damage to the case.

 

That's because the diagram that was posted is from a 550. Note the "oil pressure tensioner" (for the HY-VO chain) the shafties don't have that feature.

You can't really tell by looking at the wreckage what broke first, unless you find a piston still welded to a cylinder wall. When a motor lets go at over 5000rpm, momentum and physics go absolutely haywire in the ensuing explosion.

I don't think it was any sort of a manufacturing defect; I think it was some form of mechanical abuse, plain and simple; whether a spun bearing or seized piston I doubt it was an oversight at the factory.

 

Sure you can! There's a lot of info out there about engine failure analysis. unless you find the cause of the problem, your more likely to have the same issue again. to be honest im pretty unfamiliar with piston engines, but I can use a rotary as an example. they inject oil directly into the combustion chambers, so if an oil injector clogs, the seals go dry and the rotor would be toast. And the stuck injector would ruin every new motor until its fixed

I suppose the damage in a piston motor would be harder to read since there are more parts to get beat up inside though. but i do think your right that it wasnt a manufacturer problem. Maybe just a combination of a bad owner abusing the bike & no maintenance? I think this could have easily happened just from running the bike hard without enough oil.

yeah the end of the rod isnt cracked or anything. I would think at the very least there would be some damage from the hardware being forced out of the holes. Its like the cap just fell off.

 

I went fishing with a magnet and got part of the bearing. Compairing the two photos to this pdf guide, it looks a lot like oil starvation on page 15. The big chunk missing makes me think hot short though. on page 16.

http://docs.google.com/viewer?a=v&q=cac ... suXA&pli=1



hmm I wonder where that cap went to lol

 

If there is no damage to the end of the rod, it just means the crankshaft did not hit it, the crankshaft therefore must have hit the rod cap and forced it through the front of the case. Which would explain the missing rod cap. Trust me fellas, this damage wasn't caused by a seized bearing.

 

Sure it was. Look at the uppermost of the two pics just posted. You can see marks in that bearing pocket where the bearing shell spun in the housing. For a bearing shell to spin, it's gotta be stuck to the shaft it's supposed to be "bearing."

Rod bearing or main bearing, this one was caused by a spun bearing.

I still think gas-diluted oil together with extended high-speed running on said diluted oil was what blew this one up.