86 long rod conversion stumped
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  1. #1
    Junior Member skiddy83's Avatar
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    Lightbulb 86 long rod conversion stumped

    I have a 86 and the last thing i needed to update was the crank. So i went just normal hot rod 87-89 long rod (not stroked). Use my 86 piston which is 68.5mm. Pretty straight forward. I used the long rod crank on 86 piston with 0.190 spacer plate and the two gaskets. I been cleaning the carb and messing with jetting wondering why it was lean... then finally did a squish test with 3mm solder (1/8th). Now i'm shooting for 0.40-0.50 and I got 2.43? So basically take away 2mm and i'm dead on at 0.43 so where the heck is the extra 2mm coming from ?..... Stock cylinder and everything and the guy i bought it off of had everything on it stock except the pipe and light. Even brake covers and gold rims etc was stock so I know he didn't shave metal off the motor head or cylinder etc... Even the old head on it was pitted and stock... where is the extra 2mm coming from i can't figure out....

  2. #2
    Senior Member american opel's Avatar
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    do you have a yz250 piston?are you sure you put a lr crank in it?

  3. #3
    Senior Member Langbolt's Avatar
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    How much of a STEP do you have on the Cylinder head ? Maybe just need to have the mounting surface cut to give you the desired squish you are trying to obtain.

    What Head Gasket are you using ? How thick is it.....Maybe just need to use a CR gasket instead. (0.010" thickness)

    Post up some pics


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  5. #4
    Junior Member skiddy83's Avatar
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    I got the kit from CT Racing a quick google of trx250r spacer plate brings it up. 0.190" and the top and bottom gasket for it. No i have the long rod 87-89 with 86 piston (68.5mm). The crank was old and instead of putting a 86 crank in it so i can run the oversized piston 68.5mm, I updated it to the regular long rod (not stroked) because i didn't want to mess with port timing. Found what space plate i needed to do it and boom this is where i'm at now. I knew it was lean but the only thing i changed besides new bearings and gaskets etc etc was the rod and spacer. Light bulb turned on and I figured that was where my problem was coming from it running lean. Sure enough did a quish test and i'm coming up a few mm extra. Only thing I can think of is every peice of metal on every bike is different. What so i'm guessing is everyone is going to have to shave or machine the cylinder or something to get it down to where it needs to be. The easiest way i see of fixing this problem was have the space plate shaved a few MM and be done. I didn't want to do anything till i asked the guys on here to make sure there isn't something i'm missing or didn't do right?.... Its really not that complicated. You switch to the long rod and still using 85/86 piston you have to put a space plate in and end of story... Well I'm realizing there is a lot more too it that people aren't telling. I'm about to go out to the garage here in a min and will get some picks. I'm going to take the head off but i already know its not going to be close to top dead center. I even have a high compression copper head gasket to take up some slack from the OEM honda one but i'm still way off on MM. I never heard of using the LT crank with yz piston just the method i'm talking about.

  6. #5
    Junior Member skiddy83's Avatar
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    Well here is what i got done today before everything closed. I took off the spacer plate and ran to the metal shop. The guy couldn't shave it because of it being aluminum and trying to hold it down so he told me to go ask for Donny at another metal shop. That was the owner and he never came back before 5. So I did the math and my spacer plate is 4.826mm and I had 2.43mm squish but want to be around 0.40-0.50. So take off 2mm. I found a website that specialized in spacer plates My Business - TRX250R Spacer Plates . They had 1mm 2mm 3mm and so on. So 4.826-2mm=2.826 So I ordered a 3mm spacer plate and I will update when it gets here mon or tue. I will take pictures as i'm putting it back together and then do another squish test to confirm. I should be setting around 0.602 give or take when this is done. Keep in mind i'm running a thin copper head gasket so that plays a part in me getting the 0.602. I have a new cool head coming and ditching the old head its seen better days. Comes with 22mm dome but i also ordered a 20mm dome to and step the compression up some more. After all said and done i will have to rejet it but should see major power increase because of how far off it was. The bike is in peices now because of me pulling off the spacer plate before all the metal shops closed at 5 so I didn't have any pictures to take as of right now. I have a useless Ct racing spacer plate now that is a paper weight... Maybe make something out of it lol

  7. #6
    Senior Member acecarlos's Avatar
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    WOW...where to start.

    First:

    I assume you mean you want a squish of .040"-.050" and not .40"-.50", or .40-.50MM (.016"-.020")....Note .040"-.050" is correct range, all the rest is Wrong.

    "Had 2.43MM...so take Off 2MM...Wrong

    "I should be setting around 0.602 "...I assume .602MM? Also Wrong

    Basically & always; when using a Stock OEM cylinder (85-88) with a LR plus an 85-86 Piston kit, you need a 3/16" thick spacer plate + two .020" base gaskets (OEM Thickness is .5MM or .020")...Typically OEM factory Squish is set very high, from 2-3MM (.080"-120"), their are slight differences, however; most fall within this range.

    Cutting 2MM off a 3/16" spacer plate when using the setup above is the Wrong approach, and will yield poor results. What you are doing by cutting 2MM is drastically changing port heights and therefore timing, not the way to go. If you want to lower the squish, first perform a UCCR study, then 'Deck' the top of the cylinder to give you the Squish needed. Most 250R's will end up with a usable squish of .040"-.065" or 1MM to 1.6MM.

    Carlos
    Last edited by acecarlos; 02-07-2020 at 07:53 PM.

  8. #7
    Junior Member skiddy83's Avatar
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    Thank you carlos for the clarification but i was going by Metric on everything and using google to convert. I used normal base gaskets 0.020" or what metric said was 0.53mm and the kit i ordered with gasket and spacer plate is from CT Racing and the plate says 0.190 which converted to a fraction like you had 3/16" is 0.1875. I then put it all together and did the solder test which came out to 2.43mm. I understand the timing and port part concerning the 3mm spacer. So take the 3mm spacer off. Put the one from CT Racing back on with two new gaskets and do a UCCR before doing anything else?

    Also here is the link for the kit i got http://ctracing.net/site/atv-perform...-spacer-plate/

  9. #8
    Senior Member acecarlos's Avatar
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    Quote Originally Posted by skiddy83 View Post
    Thank you carlos for the clarification but i was going by Metric on everything and using google to convert. I used normal base gaskets 0.020" or what metric said was 0.53mm and the kit i ordered with gasket and spacer plate is from CT Racing and the plate says 0.190 which converted to a fraction like you had 3/16" is 0.1875. I then put it all together and did the solder test which came out to 2.43mm. I understand the timing and port part concerning the 3mm spacer. So take the 3mm spacer off. Put the one from CT Racing back on with two new gaskets and do a UCCR before doing anything else?

    Also here is the link for the kit i got TRX250R Cylinder Spacer Plate | CT Racing
    No need to perform a UCCR if your using the stock head, porting, and have a squish of 2.43MM...I can assure you the UCCR will end up well below 12/1; plenty safe for Pump Gas.

    Use the .190" (.1875" 3/16") spacer plate + two OEM .020" base gaskets. The 2.43MM squish is in the normal range (.080"-.120") for a stock OEM cylinder & head. In my previous post I stated "then 'Deck' the top of the cylinder to give you the Squish needed"...this is the proper way to set squish. "Deck" meaning machine the top of the cylinder only, as an example machining -1MM to 1.3MM off will give you a squish of .056" to .045"...

    If you want, you can verify by performing a UCCR with the Decked cylinder and .056"-.045" squish

    Carlos.


 

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