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Thread: yamaha 70 ces

  1. #1
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    Default yamaha 70 ces

    Just bought an old f4 cat with looks like an almost new 70ces behind it...
    Compression on all 3 cilinders are between 175 and 165 psi,
    gearcase is mod with nosecone and low water pickup.
    Has somebody standard data like compression and squish, timing? I want to find out if the engine has been mod.
    Also have the carbs of a 90hp yamaha, to fit these on the engine.
    Do you use the the reed plate and reedblocks of the 70?
    And what will be the advantage, better pick up and top end?

    btw, great forum guys...

    Jeffrey

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    Hi Jeffrey,
    Do you have photo of boat and engine, I guess if its a F4 its one I will know ??
    175 psi is the lower side of good if it has 1 piece head. If its got 2 piece head 175 is good.
    Bottom cyl is always a little lower cos the oil pump drive is missing.
    Good starting point is timing 19 deg, fuel min 98 oct, main jets 165, carbon reads, 10 mm gap. with 1 piece head.
    You can go down jet size but beware dont go much past 19 deg with timming.
    2 peice head timing 26 deg fuel min 95 oct main jets 155, 10 mm read gap.
    If its running 6j2 2 ring pistons keep eye on piston crowns and land between rings. (6J2 pistons BAD batch of piston, most fail, some still turn up as new old stock ! 6H3 work almost as good)
    Try to keep max RPM just under 8000rpm !!!! 7400-7500rpm they run and run and run !
    Find a good 11 x 19 or 11x20 prop !!!!!!
    Fit head temp gauge. lots problems come from "cold seizing" need to get temp in engine with out cooking it !
    Carl
    Last edited by Carl Kinder; 01-30-2012 at 02:08 PM. Reason: mis spelling

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    Hey Carl,

    thanks for the info.
    Have a picture of the boat when i just bought it, original stickers. looks old
    2 piece head, by that you mean a removable cilinder head?
    That is what i have...
    How can you see that its 6j2 pistons? is it possible to see true exhaust port or anything?
    Can save some time instead of open up the engine...
    Do the rings get jammed with these pistons? like merc s3000...
    When checking the carbs took a sneak peak @ the reeds, it are carbon ones. Black colour, standard ones?
    Only have a water pressure gauge and trim indicator, will see to place a temp. gauge.
    Just bought a brandnew merc cleaver 11x22, couldn't test it yet because off the wheater.
    Problem of buying a boat when winter starts...











    Grt, Jeffrey

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    Looking at your photos, looks like 1 piece cyl head. beware of core plugs in head, they pop out, use plate strips between cyl head bolts to hold them in. watch cyl head bolts (2 washers on each bolt) you can take 1 washer off on bolts you use the core plug plates on. Original bolts was too long !!!. If you deck head check bolt length again. Only use gen Yam head gasket !!.
    You can see pistons if you take exh side plate off. 6J2 have 2 thin rings, 6H3 have 2 or 3 thicker rings.
    If it has black carbon reads, that was standard for 70ces, check they seat well and no frey on edges, common problem, boyson reads fit, from memory slight mod to suzuki 185 cc reads fit !!!
    Rings only jam cos of poor quality of batch of 6j2 pistons, land breaks away near exh port.
    Check stat, most have been removed, I think its best if only part removed, leaving a choke in waterway.
    How is engine getting water, do you have pick up on bullet ?
    Lots had pickups on sponsons feeding into drilled out flush holes on gearbox with original gearbox holes blocked.
    11x22 is too big !!!
    Looks like engine is flat on transom ?. good starting point for engine height is to have lower gearbox oil plug level with bottom of sponsons, then work from there ?.
    Boat looks like old Baracuda ????? prob late eights at guess (no cell).
    I would cut the trim tab flush with bottom of cav plate and add a little to skeg
    and put steering back to one to one !! and move steering arms to the tiller arm under the engine tray. With the steering arms on powerhead bolts, engine can come loose, also can break mid section ( mid sections are like rocking horse sh*t to find)
    Depending on what you want to use it for, lots more you can do !!!!!!!!!!!!!!!!!!!!!

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    Question Very interesting posts

    In our T850 class racing here in Canada we have several of these motors. One is an out of the box original 1994 version. It was taken down to the crank at the Canadian Nationals in the late 1990's and just passed inspection. I actually contacted UIM at the time because it was so close to failing and this was an out of the box, non blueprinted, totally orignal motor. The reply I got worried me. They basically said that in Europe the inspection process was not a good as the one my motor had. Then a fellow over there sets a world Kilo record in F4 at over 100 mph. When you do the math the motor must have been turning big RPM and a very large prop..much higher than 8000. So there is a bit of history. Now the questions.

    [1] by the colour of the motor [dark blue] this a one of the early versions. Yes there were two separate spec sheets. The later one is the Yamaha grey and the cowl has the checkerboard on it. My motor has 150 lbs compression. How do you legally get to 175 lb plus?

    [2] an 11 x 20 prop or an 11 x 22 prop turning mid 7000's with a 1.71 ratio gearcase , jacked to the moon is not going to run 80 mph in my book. Then there is the 100 mph run. There must be a a trick.
    How do they do it?

    [3] I purchased a legal pure race 70CES long block from Sweden. It was no where close to legal by the UIM rule book. The motor was ported, the block decked, the head cut and the crank lightened. Question is: How would this motor pass inspection. I must have never been looked at.

    The reason for the post is to point out to my fellow Canadian T850 racers that the 70CES motors they are using are closer to the UIM specs and don't go out there and modify your motor when T850 is a stock class.

    Don Whittington

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    Don,
    I understand some of what you say,
    I have opened new "out the box" Yamaha 70ces and the porting in some places can be very close to each side of UIM spec. But I think this is more to do small production runs of the motor and the hand finishing of the guy cleaning the castings on production line !.
    Not sure you can rely on colour on paint to gauge age ? most have been about a long time. some are dark blue some are grey some are green some blocks had no paint !.
    If you take the head vol down to UIM limits 175 psi is not high, I have seen several with well over 200psi.
    After any work to cyl head, must use 99 oct 100 oct fuel, keep eye on piston crowns/ jetting
    As for engine stripping here in Europe, in the past it did get a little lax !. but then the rules on blending got "clarified"!!!!!. . lots of the old pre "clarified" blocks got dropped from World championships, Still get to see a few,,but most the fast guys are running "clarified" blocks !
    Some of the old blocks got closer to F3 than F4, and some of the fuel made your eyes water !!.
    A good well built motor will run at 8000rpm, no problem, but when you get much higher reliability is not so good.
    But on the back of a non cell old'ish boat 7500rpm, it will last all season.
    In race conditions 11x19 or 11x20 is ideal keeping the RPM in the safe side will give you 80 ish mph.
    If you are looking for any Yamaha 70 ces engines or parts or props, We have some quick stuff 2 x WC 2009, 2011.
    I can find lots older non "clarified" stuff it it helps !

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    Thanks Carl, that does make sense and matches motors I have seen over here. What could of happened was the powerheads go to an engine builder and he matches the porting on all three cylinders. Since the the porting in each cylinder is varied, the engine builder matches to the best ported cylinder and ends up with a motor way out of spec.
    I can see a 70 CES on a tunnel hull turning 7500 rpm. On the T boats we're in the 6600 to 7000 rpm range. Most T boat yamaha racers I have spoke to over there run in this range.
    We have lots of Yamahas running over here. E-mail me your list of parts and I will post them on our race site.

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    What rules do you run to for engines , do you run 60 or 70 gears ? Are you looking for complete engines or just powerheads Let me know whats good for your racing and I can find Good, fast motors.
    The Yam 70ces has been about a long time, most have seen a lot of racing, All will have been moded in some way or another, some will have been done by someone who knows what makes a motor go fast, Lots will have been copys done in a shed by someone with grinder and a shaky hand. Old engines never die they just get moved on !!

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    Carl, this thread is getting off topic, so I will send you a message.
    Don

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    Sorry Jeffrey, Don you are right !, it has gone a little astray.

    I think try what you have see how it goes first. Then if you want to go faster, start with the prop before you start on your engine !.

    I have seen lots of Yams with lots of mods that make them slower !!!!!

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