PC800 modifications

Discussion in 'Road Warriors' started by 81tiger, Nov 8, 2015.

  1. richarddacat

    richarddacat No fruit in my cookies! Supporter

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    A real nice PC has shown up on the Nashville (TN) Craigslist if anyone is looking for one.

    No relations to seller, thought there may be interest here.
    #21
  2. 81tiger

    81tiger Been here awhile

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    Okay, its 32 degrees outside, so not much riding is going to happen today, but I can get the shocks on and set the initial preload and rebound damping settings.

    Here, I put the rebound damping reference markings on. Note, the nylon washer is on but hard to see since it is pushed up against the shock body.

    [​IMG]

    The left side has a bit more room, so the washer is on this side. Here is a pic of the reference marks as seen from the back of the bike. I will dial in 10 clicks to the left based on my earlier testing. Note: you cannot see the nylon washer because it is behind one of the blue coils. This was the measurement for the bike sag (so the washer was 0.25" down from the shock body).

    [​IMG]

    I check bike sag fist by rolling of the bike off the centerstand, then push up the nylon washer to the shock body, then place bike on centerstand. Once the bike is on the centerstand, I can see that the washer was pushed down 0.25" by the weight of the bike. Based on the amount of preload on the the shock, the 0.25" works out to be a 262 lbs (this is the sprung mass of the rear suspension) load placed on the springs. I repeat the process, but now sit on the bike to check rider sag. This works out to be 0.7" as shown in this pic:

    [​IMG]

    Remember the nurd graphs, where here is where it all comes together. This graph is of the Hypercoil spring (10D0175) with the bike (green lines) and rider (red lines) sag. The dark blue diagonal line depicts the performance of both Hypercoil springs with 0.5" of preload installation dialed in. With a 0.5" preload, the curve starts at (175 x 0.5) x 2 springs = 175 lbs. It moves at 175 lbs/in x 2 springs = 350 lbs/in all the way up to a max of 1,247 lbs. The 0.7" observed spacing works out to be 23% of the total working range, so it is a good starting point. I also note by the green line, the bike sprung mass is 262 lbs (so the bike may be close to a 50/50 weight distribution). I am 195 lbs and when I get on the bike, I see the rider sag tells me the sprung mass goes to 421 lbs (a 159 lb increase). This tells me 82% of rider weight is carried by the rear suspension (159/195), so maybe closer to a cruiser riding weight distribution. I can adjust the dark blue spring curve to the left or right, but the bike sag amount (262 lbs) and the rider sag amount (421 lbs) will remain the same.

    [​IMG]

    Once I get the entire bike back together and get it back on the street, I'll post back the post mod riding adjustment(s) and first impressions. I can already tell the back is up higher, so I think the steering will be much crisper.

    Cheers
    Jerry
    #22
  3. 81tiger

    81tiger Been here awhile

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    The YSS guys came through with the correct size shock bushings today, YES!

    [​IMG]

    The old bushings press out easily and the new ones, after careful alignment, press in easy enough. When mounted, the metal on metal rotate very nicely (especially after the studs are lubed). You may not know it, but the swing arm moves about a 7 to 10 degree swing, the shock about 5 to 6 degree swing. You do not want to tighten the retaining bolt/nut so it pinches the shock bushing. This leads to a poor (harsh) rear suspension and/or squeaks.

    [​IMG]

    Now I can put the rest of the bike together tonight/tomorrow.

    Jerry
    #23
  4. 81tiger

    81tiger Been here awhile

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    She is put back together and will get out in the 68 degree weather today. Here is the last easy access to the shocks pic:

    [​IMG]

    Once back together, you can tell the rear swingarm is lower/the rear wheel is closer to the ground with the longer [~1"] shocks. THis makes it easier to roll onto the centerstand, but it means the side stand will be shorter.

    [​IMG]

    A quick check of the front forks confirms the relative rake angle is smaller (stock is 28 degrees):

    [​IMG]

    I do not think the trail has changed much, perhaps a tad longer, but this is where the new numbers compare with stock and other class of bikes (data from 2015-2012 bikes). The sport touring class is depicted by the blue triangle area. I'm a bit closer, good enough to enjoy the changes made and to be made (brakes) to the PC.

    [​IMG]

    Here is how I'll have sight access to the nylon washer to check how much of the suspension I'm using via the nylon washer. In this pic, it shows the sag:

    [​IMG]

    I'll post some in the evening how the first ride went.

    Were are the comments and questions????

    Jerry
    #24
  5. GlennR

    GlennR Chasin' my tail

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    Hey Jerry,
    I appreciate all the work you've done & sharing your photos & notes with us. I'd like to make some suspension improvements when I have more time, work space, and money. When all that materializes your info will be very useful. I'm looking forward to hearing how you like the improvements after you've ridden it a bit.
    #25
  6. 81tiger

    81tiger Been here awhile

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    Glenn, thanks for the post. All this technique I am detailing out can be used on all bikes, so all of the riders can use this to dial in their suspension.

    Here are my initial observations; I have a clearance issue on the left side. I knew the YSS shocks were a bit wider in diameter and sure enough, there is about 1" tall by 1" wide clearance issue at the bottom of the body/shock. In this pic, you can see I measured the distance to go (red) at 1.85". Since I know the whole travel at 3.06", then I know the shock compressed a total of 1.21" (3.06-1.85). When I look at the graph, I can see the 1.21" horizontal line intersects the diagonal dark blue line at 599 lbs. So, the 599 lbs + friction between the shock and trunk is the total load on the rear shocks. I was expecting to see about a 1" gap at the bottom indicating about 2" use (~900 lbs).

    [​IMG]

    Here is a close up of the clearance problem area.

    [​IMG]

    I will have to take the bottom trunk off and heat up the problem area with a blow torch - just enough to then roll the biggest 3/4" drive socket in the body and push the problem area on the trunk in about 0.5". Perhaps by tomorrow I will be done?
    #26
  7. GlennR

    GlennR Chasin' my tail

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    Be very careful using the torch on plastic. I'd try a heat gun first.
    #27
  8. 81tiger

    81tiger Been here awhile

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    Yes sir Glenn
    #28
  9. 81tiger

    81tiger Been here awhile

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    Well I didn't get any work in. The weather was unusually warm so I joined a few other fellow XL1200 riders and visited the Antietam Battlefield today. But I did get my prep done for the work ahead.

    It has been my experience the max load can be expressed as a factor of the sag load. Depending on the stickiness of the tires, riding style of the rider, road conditions, etc, the factor is somewhere around 2 +/-. So, once I fix the bodywork, I'm guessing I might see an unused gap of 1 1/8". That would indicated a max load of about 852 lbs with a ratio of (852/421) of 2.02 as shown below.

    [​IMG]

    Now, I need to account for 2 up riding. If I had a 150 lb passenger (160 lbs with gear) and 80 lbs of luggage (including the top case), I would not want to bottom out. Since the preload adjustability is not accessable on the PC800 (one downside to aftermarket shocks as the adjustment is at the top of the shock covered up by the trunk), I have to account for the 2 up load. I measured the bike sag, then the rider sag at the beginning. I could see the load difference between the 2 and could determine the percentage of the rider weight carried by the back suspension (a tad over 79%). The passenger weight has a greater percent weight (90% estimated) on the rear suspension because they are further back on the saddle and the luggage/crap in them is at a higher weight percent becuse it is further back too (estimated 97.5%). This table lays out the observed loads solo and estimated 2 up max luggage.

    [​IMG]

    Graphically, this is what the 2 up load looks like on the current suspension (spring preload). You can see based on the solo rider loading ratio (2.02), the 2 up loading could be about 1,300 lbs which is greater than the max load the spring is currently set up for (1,247 lbs). That means I'm likely to bottom out from time to time. The best way to prevent this is to increase the reload setting.

    [​IMG]

    If I increase the preload setting from 0.5" to 0.7", that should be enough. Since I have to remove the trunk to fix the interference, I will increase the preload setting to accommodate 2 up riding potential. The change will look like:

    [​IMG]
    NOTE: I made an incorrect reference to the spring curve moving to the right. This is incorrect. The spring curve shifts up or down in the "Y" axis depending on the preload distance.

    So, the riding envelopes would look like graphic below. The solo riding is biased to give me the best riding geometry (rear up) and the 2 up keeps me from bottoming out. If I had access to the preload adjustment, I would use a lower rated spring (155 lbs/in, about 12% less stiff) and set up a greater solo riding envelope. As it is, I will have to do with the shorter working range and will have to make sure I get the damping right. With the way it is now (rubbing), it is harsh and a bit uncontrolled in turns. I expect to sort that out once the trunk is off and reworked.

    [​IMG]

    I will be out and away next weekend as the son graduates from college so it will be a couple weeks before updates are made.

    Is anyone (PC riders) going to start experimenting (besides Glenn) anytime soon? I can help you dial in your suspension if you know your weights since I have the springs calibrated.

    Jerry
    #29
  10. 81tiger

    81tiger Been here awhile

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    Thanks Pinkius. I will have the wheels powder coated at some point. I think after the front brakes are done so I can get the fork sliders and caliper offset brackets done (in the same color) the same time I am getting the wheels done.

    Some tuning help for the PC riders running stock rear suspensions. Here I am testing to see how the different rear springs test out. Here is the the non adjustable shock/spring looks like:

    [​IMG]

    Here is the adjustable shock. It has a linear rate spring that is more stout than the other side.

    [​IMG]

    And here are the test results. The weaker spring has a dual rate (44 transitioning to 150 lbs/in) and the stronger spring at 166 lbs/in. When you combine the springs, it nets a dual rate (105 transitioning to a 158 lbs/in single spring rate. The max capacity with no preload dialed in is 1,035 lbs before bottoming out.

    [​IMG]

    So, if we look at the expected performance of the shocks with no extra preload dialed in and look at the case of setting sag at 25% of the working range of the shock, we get this graph. 25% of 3.5" = 0.88". Looking at 0.88" across to the magenta line, we see it corresponds to a 338 lb load through the 2 springs. Take out the affect of sprung bike weight of 262 lbs and adjust the weight since it only represents the sprung weight of the rider, and you get the design weight of the solo rider at 95 lbs.

    [​IMG]

    Typical rear shocks come with some preload adjustability (typically 4-5 indents); in the case of the PC800, we have 4 indents to select from. In the case of the PC, going from 1st indent to the 4th, the spring is compressed 0.6". Not much, but what is the affect on the allowable solo riders weight if we hold to setting sag at the 25% mark?

    [​IMG]

    So we dial in all the preload moving the curve of stronger spring 0.6 in down. This is what happens to the curve; we pick up an extra 100 lb of capacity.

    [​IMG]

    When I combine this new curve to the nonadjustable shock spring, I get this new purple spring curve. The max capacity goes from 1,035 to 1,135.

    [​IMG]

    Now, if I check what capacity of the max preload case, holding the 25% sag percentage, I see the max load is now 221 lbs.

    [​IMG]

    Since the preload indents are linear, I can build a graph to show the relationship between indent selected and weight I can carry if I am using the 25% guideline. It is a disappointment, the user manual doesn't have something to guide you into which preload indent to select for your solo riding weight. But, since Al Gore got us all the internet, I can now share this with you. Example 1: In this graphic, if you weigh 200 lbs (with riding gear), you follow the red vertical line until it intersects the thicker dark blue diagonal line (the 25% line) and then trace a line to the left. You see it hits the vertical axis between the 3rd and 4th indent. If you ride solo all the time and don't carry to much, pick the 3rd indent. If you carry stuff and/or you ride a bit more aggressively, pick the 4th indent. Example 2: if you weigh 150 lbs you follow the blue line. This works out for you to use the 2nd indent. So, now you know which indent you should be using for your riding weight. Let me know if this isn't clear for your riding weight and I will post back which indent to use. If you weigh more than 220 lbs, let me know it you are trying to run the oem set up. You just need to cut and install a small spacer to further compress the stronger spring. You could do like I did and swap oem spring to run 2 stronger springs, but you don't have to do this. The cheaper fix is adding the small spacer to increase the preload on the single stronger spring.

    [​IMG]

    So now I can compare how I would have run the oem set up to the one using the YSS shock/hypercoil 175 lb/in linear rate spring. The oem setup with max preload dialed in has a larger riding envelope than the YSS/Hypercoil set up (1.81" vs. 1.23"). Relatively speaking this is a notable difference, but in real terms, I don't think I will notice it that much. On the smoothest of roads, the oem set up will be notable smoother, but I think you wouldn't notice the difference much once I fix the trunk clearance issue.

    [​IMG]

    Speaking of fixing the trunk, I don't think I will get this done until Tuesday.... An unexpected death in a close family + relative here in the house will limit time to get work done.

    Jerry
    #30
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  11. IMaScot

    IMaScot Been here awhile

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    Ahemm. Most of the guys here don't have the time or resources to duplicate your excellent work. I would suggest a pair of HAGON shocks set on the middle spring position. Slam down your money and walk away. To easy. If you really want to get the most, buy a Michelin Commander 140/90 for the rear. You will not regret it.
    #31
  12. IMaScot

    IMaScot Been here awhile

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    One more thing. There is a lot of power hidden in that bike. Honda choked off all the guts at the factory. To see the solution, look at our site.
    #32
  13. 81tiger

    81tiger Been here awhile

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    IMaScot,

    I have been following your most excellent work in the other thread and agree. It is on my list of things to do. My only change to that plan is to swap the cams out dropping in a set of cams from a VT800. They will open up the breathing a bit more so the intake and exhaust changes you cite will be further enhanced.

    HAGON shocks would be nice too, but I went with YSS shocks. I will have to pass on the Michelin Commander as there is lots of life on my Perelli Angel GTs.
    #33
  14. chornbe

    chornbe The monkey's football Supporter

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    Do we know if the NV700 (later deauville available here in the US) rear wheel will work where the 650 did? I'm cool with creating my own caliper mount setup for the change to discs, but would prefer to not get into cutting/making spacers and bushings. Thanks.
    #34
  15. chornbe

    chornbe The monkey's football Supporter

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    What site?
    #35
  16. GlennR

    GlennR Chasin' my tail

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    #36
  17. 81tiger

    81tiger Been here awhile

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    Yes, the NT700V rear wheel will work.

    I was getting close to finishing the PC800 project when I noticed how similar the rear final drive looked to the one on my 1984 CB700SC Nighthawk. So, I decided to take off the Nighthawk rear wheel and tried to mount the NT650V rear wheel; it fit! Thats when I moved forward to making a mod to upgrade the front and rear wheels on the Nighthawk using the NT700V wheels since they had the straight spoke designs (at an angle) vs the oem wheels.

    A pic of the Nighthawk with the swapped wheels vs oem set up. With the new brakes up front and better suspension, the Nighthawk was a blast to ride.

    Je pic for internet.jpg oem bike.jpg rry
    #37
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  18. chornbe

    chornbe The monkey's football Supporter

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    Oh man.. the SC remains one of the most badass bikes ever made. Damn, but i love those things.

    nicely done.

    Even the 16" wheel on the Nighthawk allows for better tire options than this asinine 15" mess that Honda uses(used) for so many of its bikes. (sigh)

    I have a sport scooter radial on the back of the PC800; I had the same tire on the Magna a few years back and it performed much better than it does on the PC. The PC is just a lot closer to the tire's natural weight load limits. (I thought it was a load rating 69, turns out it's a 67)

    Modding the PC up with the 17" wheel is my next thing, I guess.

    Is that the Deauville caliper hanger/carrier on there, too?

    Thanks, man!
    #38
  19. 81tiger

    81tiger Been here awhile

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    The caliper and bracket are from a mid 90's Triumph bike that used under axle set-up on several of their bikes. The set up is for their 255mm rear disc, but it works well with the Honda blackbird 256mm rear disc. That disc bolts up to the wheel. The bracket mounts with stock axle and the brake stay is the PC800 drum brake arm. Its a straight bolt up effort. The hardest part was fitting the rear MC. USed a VT1100 MC with long actuator arm. Had to flip the tie in to the rear brake arm so it compresses the MC vs pulls the drum brake.

    Jerry
    #39
  20. chornbe

    chornbe The monkey's football Supporter

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    Thanks for the info; I hit eBay yesterday, found a wheel, and gathered a gaggle of lower-cost brake parts of various ilk. I'll start in on this project in a couple weeks.

    Thanks, man!
    #40