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XJ750 With Locked up Engine - Advice to a Beginner

Discussion in 'XJ Technical Chat' started by Jack Duane, May 26, 2021.

  1. Jack Duane

    Jack Duane New Member

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    Good evening all, I am brand new to owning a motorcycle. I've ridden a bit but this is my first bike and it's in rough shape. My hope is to use it as a learning opportunity to better understand bike mechanics with the ultimate goal of ridding it. According to the seller, the bike has all of the parts (although I'm a little suspicious) but the engine is locked up. Beyond that, he didn't say much but I can see that the last time the bike was registered was back in 1998 so it's been sitting around for some time. I've worked on cars, tractors, and lawnmowers previously and have some general mechanic tools but have never doing anything with a bike. Is there anything I should know before I dive in? I'm under the impression that the engine needs to be rebuilt. How difficult of a job is that? I don't mind throwing lots of time at this but finances are limited (aren't they always?). Any advice or recommendations would be much appreciated. In the mean time I've been watching all of the relevant YouTube on engine rebuilds and old bikes to make up for my knowledge gaps.

    Here are a few pictures of the bike (seat isn't pictured)
    IMG_20210522_133947.jpg IMG_20210521_194443.jpg IMG_20210521_194625.jpg IMG_20210521_194450.jpg
    A. Gates
     
  2. Jetfixer

    Jetfixer Well-Known Member

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    If you can free the engine up , good chance it can run . First remove the spark plugs pour about 6 to 8 ounces of a mixture of ATF and Acetone down each plug hole. Let this sit for several hours , repeat this again let it sit. While your waiting remove the left crank shaft covers ...if it has sat as long as you say an impact driver maybe required to remove screws there are four on cover . Once this is removed use a 19mm wrench on the nut only try to turn it COUNTER CLOCKWISE see if you can move it . If you can get it to move then you can see if it will crank with the starter. My Johnny Cash bike (one piece at a time) was a swap meet purchase for 100$ it was a frame and an engine and a few parts ...yours is more " complete " just take your time invest in a Haynes manual and by all means ask questions. Cheers
     
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  3. Toomanybikes

    Toomanybikes Well-Known Member

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    One more trick is after you pour the juice into it stick it in gear and gently rock it back and forth for a few minutes each day for a week. Then if that hasn’t loosened it up get a heat gun and warm the cylinders for 5-10 minutes and repeat the rocking in gear for a few minutes and do it twice a day for another few days and it will work otherwise start looking for a spare engine as oversized pistons and rings aren’t available. If it’s that stuck the rust will be so deep that it will be useless to make it work.
     
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  4. ManBot13

    ManBot13 Well-Known Member

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    I started my motorcycle mechanic journey on an XJ750 Seca, so there is definitely a lot you can learn and do, especially with all of the details information on this forum about restoring these old bikes. I'll give you a few words of advice:

    1. There are no carbs on the bike. I assume there's a parts bin where all the parts not in your picture are living. Was it stored like that before you bought it? Outside? The valve timing of these engines means that basically one of the exhaust/intake valves is open on one cylinder at any time. If nothing was covering the intake, and it was outside, there's probably a lot of water/corrosion in at least one of the cylinders. So follow the advice above to get it unstuck, but don't commit to the engine until it's in good enough shape for a compression test. Rebuilding XJ engines is usually a lot more expensive than finding a rough bike with a good engine that blows good compression.

    2. Don't be in a hurry. If you really want to learn to restore the bike to a reliable condition, make peace with the fact that you probably won't be riding this year. It gets hard as you see and hear more and more motorcycle ride past on a nice day.

    3. Focus on operation first, looks later. I made the mistake of dreaming about what color I would paint the bike, and it delayed me at least six months. Think about reliability and safety. Never skimp on important things like brakes, steering head bearings, and tires.

    I'm not that far from you in Fairfax. So if you're really stuck, give me a shout out. I've moved on from XJs, but I could certainly lend a hand.
     
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  5. Jack Duane

    Jack Duane New Member

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    Thanks everyone, this is exactly the kind of information I was hoping to receive!

    Jetfixer: Does it matter what kind of ATF fluid or is it all about the same when used for this purpose? I've also read that Marvel mystery oil can be used for breaking loose the pistons. Any thoughts? I'm happy to do whatever will work best but there is a convivence to buying a pre-made solution. Especially if I can get it from Walmart for $3.50 for 32 OZs. As for cranking, the bike doesn't have a battery. If I get this far, is there a way for me to test it without buying a battery? Can it run without one without causing damage or is that a non-starter?

    Toomanybikes: I assume the heat gun would be directed into the sparkplug opening? Is it more of a low and slow heat or a hot and fast heat?

    ManBot13: Points taken. I had already anticipated that I wouldn't be riding until next spring/summer but I'd be lying if I said I wasn't hoping for at least a few test drives over the winter! Yes, there is a parts bin not pictured. A brief scan seems to indicate that most if not all of the parts are present for the carbs. The person I got the bike from told me that the diaphragms weren't any good. Any suggestions on where to get replacements? A quick look at eBay and a few other general sites seems to indicate that carb rebuild kits are out there. I don't know for sure if the bike was stored outside for the past several years or not but I am fairly certain that it was outside and only partially covered for at least the past 6 months. I actually got the bike for free so I haven't "lost" anything yet. Good to know that rebuilding probably isn't worth it. However, if it's a question of labor I'm happy to put in the work if I can find parts at reasonable rates. Also, glad to know I might have some assistance not too far away, thanks for offering.

    As a general rule with XJ750 engines, are there any red flags (like a seriously corroded piston) that would indicate that the engine isn't worth the effort? Are there any parts that are particularly difficult to replace or find? Also, are there any particular tools that would make the work discussed above easier or that are considered a "must" for rehabbing a bike?

    Again, really appreciate the quick comments and support. As I make progress I'll be sure to share with the group!
     
  6. Jetfixer

    Jetfixer Well-Known Member

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    Any ATF will work, Acetone can be bought at Wally world or ACE hardware . A battery can be bought at Wally world as well last time I bought one paid like 40 $ ( both my bikes run AGM sealed batteries not cheap but in my opinion the best) . My Johnny Cash bike was bought at a swap meet in October 2020 as frame and engine and worked over winter had it running by January. Bought parts off eBay, friends, and xj4ever. If and that is a big if the top end is roached, the head , cylinders can be replaced, xj4ever should have the gaskets and piston rings , you need to figure you will have 300 to 600$ in parts to get it sorted , and the self satisfaction that YOU did the work . Some folks may tell you don't waste your time ...just buy a new bike or one that runs ...but where is the fun in that ??? I've owned Honda's, Kawasaki, a Buell, and of course Yamaha's . I would recommend making a list of things you will need a few items ..Fork seals, brake caliper seals , battery, recommend upgrade to blade type fuse block , carb rebuild kit ( even my wife could rebuild carbs ...so I'm sure you can to ) ( recommend contacting xj4ever for butterfly seals just ordered a set 40$ this is a must replace item) look closely at the tires both my bike run Shinko gave like 65$ each and mounting and balancing by my local yamaha dealer was like 50$ each . While you have rear tire off replace rear brake shoes. Some items are safety items IE: to keep you safe and upright :D ....you can do this and you will get all the help on this site many of us have loads of experience with bikes. Cheers
     
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  7. Minimutly

    Minimutly Well-Known Member

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    IMG_2072.PNG IMG_1254.JPG If you get the engine to turn over you have a hope of getting it running. I wouldn't rush to buy a battery, you might need an engine...
    My seca was like this, i did the atf amd acetone thing and it did free up, now it runs sweet as. But, I have a long way to go to make it anywhere near perfect - the frame is tusted, so engine out, the carb tops are rusted, the seat needs recovering, it all needs painting, the brake master cylinder and callipers, as well as the rear shoes need rebuilding and replacing, I've replaced the rubbish glass fuseholders, rebuilt both handlebar controls - you get the picture here? The list goes on but I'll leave it there.
    Get it turning over, rebuild the carbs, fit a batter, and fingers crossed - oh, drop and replace the oil, you never know how much water is in there.
    Keep us all updated...
     
  8. Timbox

    Timbox Well-Known Member

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    Let the mixture you pour into the cylinders work for you. Let it sit for a week or so. If that engine was outside and stored without the carbs on them I feel water may have gotten into the engine. If you drain the oil you will find out if water go in. If so, you might have a really challenging time with that motor. If water got into a cylinder and started to rust the rings, well engine rebuild time...maybe.

    So, once you check the oil for water and just leave the solution do the magic for you. In the mean time, click on the upper right corner of any of the pages on the forum. You can read up about your bike and all the things you will look forward to doing. Cost of the rebuild, taking the carbs to "church" and even the electrical system overview.
     
  9. Jetfixer

    Jetfixer Well-Known Member

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    The xj engine is a rugged design the only real problem is the starter clutch and the chain guide that can break up. Do not write your engine off , if you free it up a compression check will tell you the condition of the engine a reading of 130 psi to 150 psi is good 90 psi or less is a problem , 0 psi ...a hole in a piston or bent valve. Buying a used engine is an option ...but the VIN will not match to some that is important and some to BMV . Buying another engine unless you see and hear it run is can be a gamble , swapping out engine is not real difficult a milk crate some 2x4's, a helper . Make sure to go to the upper right corner of the page to xj4ever click it on read the overload hour and to order parts start an IM message to chacal, I order parts from him with PayPal very easy and great service.
     
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  10. Minimutly

    Minimutly Well-Known Member

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    Plus one for ordering from this chacal guy - you'll get genuine or as good as genuine parts, not cheap chinese fakes. Shame it costs so much to get stuff to theUK...
     
  11. Jack Duane

    Jack Duane New Member

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    Alright, I'm going to put the fluid in the sparkplug holes now. I'll probably check every few days by rocking it back and forth in 2nd gear just to see if I can get any movement. Hopefully tomorrow I'll be able to drain the oil and see what condition it is in. I'll keep you all posted. Looks like I have a lot of pleasure reading ahead of me to get a better handle on the bike and it's systems!
     
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  12. Jack Duane

    Jack Duane New Member

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    Hey, dumb question here but how do I tell if I have a XJ750 Maxim or a Seca? I've seen people talk about both but can't seem to find anything on the bike that would indicate the type to me?
     
  13. Jetfixer

    Jetfixer Well-Known Member

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    You have a Maxim, engines are the same in the Seca and ,Maxim ...the Seca was the " sport" the Maxim was the more " cruiser style" . The tank and seat , handle bars, cluster ,forks , tail light rear fender are different .
     
  14. Toyobaru866

    Toyobaru866 Active Member

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  15. Jack Duane

    Jack Duane New Member

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    Good stuff, thanks!
     
  16. XJ550H

    XJ550H Well-Known Member Premium Member

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    if your photo is your bike it is XJ750J maxim 1982. the tank is the first giveaway the second is the handel bar style for that year. the 83 has tublar bars and round headlight

    the seca has tube style handle bars with covers on them
    this is a seca style
    https://www.motorcyclespecs.co.za/model/yamaha/yamaha_xj750_sega 81.htm

    if you look at Jetfixers photo the style of the tank and flow into the side covers is seca style
     
  17. XJ550H

    XJ550H Well-Known Member Premium Member

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    the motor mounts on the motor have same dimentions but 1 motor has solid ant the other has rubber mounts
     
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  18. XJ550H

    XJ550H Well-Known Member Premium Member

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    this is what your bike looks like
    [​IMG]
     
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  19. Jack Duane

    Jack Duane New Member

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    It's nice to know what the "goal" looks like. With any luck I'll be there eventually! I went out and rocked the engine in 1st and then 2nd gear today to see if there had been any improvement since I added the fluid on the pistons but still no luck. I know it can take several days to over a week but I'm just excited to see any signs of life. Out of curiosity, would there be any advantage to rocking the bike back and forth in a higher gear or is 1st/2nd sufficient?
     
  20. XJ550H

    XJ550H Well-Known Member Premium Member

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    centerstand bike and you can pull on the rear tire
     

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