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  1. #1
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    89 xr4 black max 150 rebuild questions /advice

    Quick summary bought boat after had sat 3 years as guy couldnít get it running right. Everything was original and was dropping cylinders at idle on ears. So I did all new electrical cdi replacements and new wires. I had already done plugs and rebuilt carbs as he started that and had a mess.
    Always had 120-125 compression hot or cold so didnít think had a problem but pulled heads and found 2 cylinders were blown into water jackets. So had heads cut Iím now at 36cc from 40cc. Put back together and wot boat ran great on the water but I couldnít get it to idle down. I had to retard the idle timing to around 18 atdc to get close to 700/800 and it was rough and ran hot going slow.
    my guess was some sort of air leak but pulled lower to check my water pump anyway. Thatís when I saw tons of Milky oil which was not there before on the bottom of the motor. Looked like lower crank seal leaking is my guess.
    I also pulled the middle plate under coils and saw two skirts pretty trashed which surprised me with the hood compression hot or cold. Also the engine to lower that bottom gasket was completely blown out from the exhaust to the water jacket also maybe why ran hot at cruise? So by fixing all my issues I created more or uncovered more.
    So itís all apart I got two beat up pistons on the skirts cylinders are really good where rings ride and below the transfer holes is where itís a little are up and I can feel some scratches. 2 is worse then 4 those are the two which pistons were scratched. All others are really good. Pistons look good bores great I assume with the good compression still I will be ok with a hone and new pistons in those two holes and re ring the rest or put 6 pistons in it as I found some with Teflon coated skirts which might help on an older motor which Iím sure is a little loose once I hone it.
    So that is one question do 2 or do all 6 with a better piston ?

    Anything I should do to help motor run better stronger when apart? Clean up ports ? Do any tricks some of you guys might know? I raced nitro r/c so know a little sleeve or port work can do wonders on a motor like this. I just donít know if anything simple is worth doing as not familiar on these like the little motors I modded.

    The crank has what looks to be rings like a piston they look fine but should they be replaced ?
    Anything else while in here? Not looking to spend a fortune but I want it right as going to trade it or sell it next year as wife wants a ski boat. She is scared of this 17 foot Norris craft. Itís also a 1989 and in mint condition shines like a new boat I donít think itís ever been stored outside a day in its life. So super nice boat so want it to run well also.plus I want to have some fun with it while I still got it and be trouble free.

    thanks for help and any advice.

  2. #2
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    subscribed as i have the same engine

  3. #3
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    First of all welcome to the site. You will likely get more opinions than mine and that is a good thing. In my opinion if you can feel the scratches the cylinders need bored. You can do just the two bad ones but if you install new pistons most likely the new pistons will transfer the scratches to the piston skirts and you will be doing it all again. Those are good motors. You can clean up the rod slots but do not enlarge them. Re-using crank rings is fine as long as they turn freely on the crank. Take your time and have some fun.

    Rock
    Team Junk

    No sparkling wiggles in here, only dump truck grinches.

    "Screamin Heathen"

  4. #4
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    XR4's were made in 1988, 1989, and I think some in 1990. I still run an early one from 1988 which has vertical reeds. The later ones I think went to horizontal reeds. In any case so far I have never needed major engine work. Have replaced the reeds with CCMS composites, the stator once, normal maintenance, and I just started running an external fuel pump with it which I really like so far... no need to pump a ball and it starts and idles more reliably. Still using oil injection, but took off the idle stabilizer box.

  5. #5
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    Look for the “Cherry 2 Fo” or something like that posted by a guy called something like Trex. Welcome to the slippery slope…
    Josh Peterson

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  7. #6
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    If ya got it all apart and taking the time to fix it. I would suggest getting with someone or a machine shop that has bore gauge and get them checked. The cylinders could have taper, out of round, or slap wore out and they will look fine to eye. If they are fine dimension wise, hone ‘‘em and replace necessary pistons. But, I bet you’ll find sumpin out o’ whack on the scuffed ones that caused it to begin wit.

  8. #7
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    Hey fellows, is this a steel sleeve motor or chrome?

    welcome to Scream and Fly, Lt1. Lose the black boxes and oil injection. Check your compression as you might need to run premium. Lastly, get new Sierra switch boxes if yours are way old or even original. Get the ones made in Germany. About $350/pair.
    1990 Shadow bass boat w/ 2.4 200 Merc. Totally resto'd boat and love it!

  9. #8
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    justa little info on that motor which imo makes it not so desirable to try and "make more horse power"...tha xr4 is merc's first (believe only) production steel sleeve 2.4.. was built from '87 ta '90 maybe.. it has its quirks.. one of which thats its famous for is tha slightly "turned" sleeves... some more so than others??? don't know if thats a standard for it or justa a manufacturin' error... rebuilt tha right way it can be a very dependable 150/160 horse power motor...

    ???.. how many water intake holes on tha side of tha gear case?

    rexy's "cherry 2 fore" is built off a chrome bore block.. completely different deal...

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  11. #9
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    Quote Originally Posted by tlwjkw View Post
    justa little info on that motor which imo makes it not so desirable to try and "make more horse power"...tha xr4 is merc's first (believe only) production steel sleeve 2.4.. was built from '87 ta '90 maybe.. it has its quirks.. one of which thats its famous for is tha slightly "turned" sleeves... some more so than others??? don't know if thats a standard for it or justa a manufacturin' error... rebuilt tha right way it can be a very dependable 150/160 horse power motor...

    ???.. how many water intake holes on tha side of tha gear case?

    rexy's "cherry 2 fore" is built off a chrome bore block.. completely different deal...
    This has 4 intake holes in the lower. I didnít know if some easy tricks to more hp that were relatable and worth the trouble. Like I cut the heads already a little to 36cc

  12. #10
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    This thing ran strong on this Norris craft 1750xl. I don’t know if just light boat or motor ram well even with the two scuffed pistons. 4 blade 24 pitch prop 65 mph on the gps and had my wife not freaked it had more in it. Was a bit rough and probably out of water more then in at that point. Lol and it was still trimmed all the way down.

  13. #11
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    Quote Originally Posted by rock View Post
    First of all welcome to the site. You will likely get more opinions than mine and that is a good thing. In my opinion if you can feel the scratches the cylinders need bored. You can do just the two bad ones but if you install new pistons most likely the new pistons will transfer the scratches to the piston skirts and you will be doing it all again. Those are good motors. You can clean up the rod slots but do not enlarge them. Re-using crank rings is fine as long as they turn freely on the crank. Take your time and have some fun.

    Rock
    I see your point on the cylinders if it was up in the area the rings ride. The small scratches are all below the transfer ports where ring isn’t reaching. On a two stroke I don’t know how important that is to seal or just stability of the skirt. It had the same 120/125 compression as all the other cylinders and why I was so surprised to find the problem.
    this all started with I couldn’t get it to idle down like a bad air leak. That’s once I fixed my blown head gasket which was the other side of the motor. 2/4 are the pistons with issues on skirts. 1/3 had the blown gasket into the water jacket. It idled good at 800 with the gasket blown but soon as I fixed that then it wound t idle down at the same 4 degrees atdc timing. I need to post some pictures also as maybe someone can say yes that gasket blown can cause the problem. But motor ran strong wot I had timing so low on it to not tear up the lower it was causing issues on the hole shot I believe and maybe causing it to run warm. I say hot earlier but 3/4 on this cheap gauge was max I saw. Most of the time it was straight up no numbers but with inferred temp gun I saw 160 at the head on all cylinders. I didn’t have it on the water with me to check what it was at 3/4 on this gauge.

  14. #12
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    Quote Originally Posted by rgsauger View Post
    Hey fellows, is this a steel sleeve motor or chrome?

    welcome to Scream and Fly, Lt1. Lose the black boxes and oil injection. Check your compression as you might need to run premium. Lastly, get new Sierra switch boxes if yours are way old or even original. Get the ones made in Germany. About $350/pair.
    Oil injection gone already. I replaced all electronics with new cdi parts already. No black box compression was 120/125 on all cylinders hot and cold even on the two with scuffs. It’s a steel sleeve so no chrome.

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  16. #13
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    Quote Originally Posted by FORBESAUTO View Post
    If ya got it all apart and taking the time to fix it. I would suggest getting with someone or a machine shop that has bore gauge and get them checked. The cylinders could have taper, out of round, or slap wore out and they will look fine to eye. If they are fine dimension wise, hone ‘‘em and replace necessary pistons. But, I bet you’ll find sumpin out o’ whack on the scuffed ones that caused it to begin wit.
    I think the previous owner got it too hot and possibly the pistons came when oil injection failed and he continued to head back to dock. I can tell the rod ends are blued slightly on the sides and so is the crank at spots. The crank has no scratches at all just some color like got hot. Seen this in v8s I have rebuilt in the past.
    it looks to have had lube issues on those cylinders I actually have a dial bore gauge so once find spec for pistons I’ll figure it out.
    it took me a week of running around here trying to find a shop to attempt to cut my heads. He managed to do it and it’s right I checked the ccs on the combustion chambers to make sure cut true.
    I do worry about trying to get someone to bore the two holes and not mess it up. Seems all the old timers that did that work around here are now dead and gone and no one wants the work of marine though I live where there are tons of lakes.
    I was very surprised to find the problem as ran well other then high idle. Good compression and very strong up top. I’m going to run a hone through it and see if can clean it up and not be out of spec. This is where a few thousands over size piston would be nice. Lol but maybe can do it and be at the loose side of it as only the one has marks which are below transfer ports and not affecting ring seal.

  17. #14
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    Ok so pictures of some of the things I found. The one of the carb is the upper jets idle I believe had o rings not the gasket both sides torn and probably leaking. I kept seeing some fuel show up and sure thatís why on front of motor. That was on the lower carb.

    rear seal pic and pic of the lower. Itís got tons of oil and grease in that pocket so maybe the rear seal had a leak? Iím not sure where else this accumulation can come from.

    piston skirts can see the scuffs and some metal transfer maybe. The pic of the cylinder thatís the only spot and looks to have aluminum stuck in the sleeve so might clean up easier then I think. To me it looks like lack of oil and the skirts started to drag and tore them up. But only on those two the rest look really good for how old it is. Can still see the cross hatch in some of the cylinders and no wear on pistons on most of it. A little blow by at the rings is the worst of it and probably due to this thing had a ton of carbon in it when I got it. Tops of the pistons were thick and Iím sure rings got stuck. I had to do a hell of a decarbon on it.
    I tossed the old head gaskets or would show the blown spots.

    looking for someone that knows these well maybe can help explain what these kind of gasket problems and the pistons can do for how it was running.

    had it idled down to 800 and normal Iíd never even gone looking for a problem or tore it apart. So this all started when I fixed the two cylinders that were getting water Nd not burning strong. Once I did that the idle was too high to do anything.
    Attached Thumbnails Attached Thumbnails image.jpg   image.jpg   image.jpg   image.jpg   image.jpg  


  18. #15
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    My comment had nothing to do with compression loss. It was more about getting it right as you plan on selling it.

    Rock
    Team Junk

    No sparkling wiggles in here, only dump truck grinches.

    "Screamin Heathen"

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