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Old 09-12-2016, 02:16 PM
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Default 98 CR500 engine setup help

     

Hey Guys,

I'm looking for help from experienced CR500 builders.

I just went through a 1998 cr500 engine top to bottom and put it in a 2006 CRF450 frame. The engine has a 89.5mm weisco piston, rebuilt and balanced crank. It was ported and the head modified. After break-in, a leak down check showed 8% at 100psi at TDC, a compression test showed 140psi kicking it over with the throttle open. The bike is not running any better than a stock motor, feels low on bottom end and has started to detonate under load. It has 9 hours on the hour meter.

I'm running 50/50 91 e10 pump and VP110 fuel, Super-M at 36:1, procircuit pipe, 38mm airstriker carb, stock cage with TDR reeds. Ride at 4200' elevation.

I ride it hard in the sand and really want to get it straightened out so it makes good power from mid to top.

I would appreciate any help or ideas on things to check. I'll be pulling the head to look at the cylinder and get the CC and squish numbers.

Also would really appreciate any recommendations on porting shops that know CR500s.

Thanks,
Jon
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File Type: pdf BECK_500.pdf (369.2 KB, 17 views)
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Old 09-13-2016, 09:56 AM
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Quote:
I just went through a 1998 cr500 engine top to bottom...The engine has a 89.5mm weisco piston, rebuilt and balanced crank. It was ported and the head modified
I'm not sure where to start. When you say "I just went through", what does that mean? Did you personally tear down and rebuild this engine and fit it with the parts and
modifications you described? I ask this because you don't seem too sure about the port work and your "leak down" test was incorrectly done.

The leak down test you described with the piston at TDC and that kind of pressure is used on four stroke engines to check pressure loss due to valve seals and piston ring
wear.

A proper two stroke engine leak down test starts with placing the piston at BDC and pumping the engine to around 6 psi. Then time the pressure loss looking for no more
than 1 psi a minute. Pumping up your engine to 100 psi - I'm not sure how you can even do that, did you use a compressor? Anyway, that kind of pressure probably
wrecked your seals and gaskets to the extent that you may have had a tight engine before the test but not anymore as evidenced by the 140 compression test.

You have a mess on your hands. I would concentrate on getting the basics done correctly. Tear it down to the cases and replace all the seals and gaskets. Once you have
a tight engine as indicated by a proper leak down, you can address any issues you may have with the port and head work.

Good luck and welcome to ATM.
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Old 09-13-2016, 11:31 AM
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Dogger,

Thanks for the reply. I have seen a few of your posts on 500 build ups and was hoping you would chime in.

Yes, I personally disassembled the engine and inspected all transmission parts. I cleaned the cases and replaced every bearing, seal and spring with OEM Honda parts.

The cylinder was sent out for a re-bore and head work. I don’t have the knowledge to be able to alter port design so I relied on the professionals who do. What I asked for was a fast setup designed for mid to top desert/dune riding.

You misunderstood my intentions for performing the leak down test. I performed it correctly for what I was looking for and that was ring seal. The bottom end did not see any pressure as the piston was at TDC so the small volume of air leaking past the rings exited the intake and exhaust. The leak down was done to find out where the low compression was coming from. I’m trying to figure out if the head work created too large of a chamber or if the rings are not sealing. Leak down results suggest too large of a combustion chamber or too tall of an exhaust port.

The test you suggest is for checking bottom end seals only, I’m not concerned with that right now.

I appreciate your reply, but you have to admit, you jumped to conclusions and came back with a strong reply. I don’t have anything near of what you say is a mess.
In my original post I included a PDF of what the engine looks like, this wasn’t a thrown together pile of crap.

Jon
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Old 09-13-2016, 12:26 PM
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If it were mine I'd start by measuring the squish, CC'ing the head and fitting a degree wheel to record port timing, at the very least the exhaust port.
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Old 09-13-2016, 01:10 PM
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Quote:
Originally Posted by Faded View Post
If it were mine I'd start by measuring the squish, CC'ing the head and fitting a degree wheel to record port timing, at the very least the exhaust port.
Thanks for the advice Faded. I'll get those numbers this weekend. I finished the bike this spring and was hoping it would rip. I'm bummed its currently as fast as a stock CRF450.

Is the best method for measuring quench the solder pinch above the wrist pin?

I'll search the forum for port timing measurement technique and get a small degree wheel. I'm very familiar with degreeing cams so I get the idea of port timing. Do you have any tips?

I have always sent my cylinders out and just assembled them trusting the machine shops measurements. Unfortunately the shop I loved to use is no longer in business, so I'm in new territory...
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Old 09-13-2016, 03:31 PM
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It's never any fun when it doesn't work quite like you expected. The solder method isn't the best, but it works good enough. For me I remove the head and lay a piece across the entire bore, in-line/above the wrist pin to avoid any rocking of the piston. The pros use clay. Shine a light through the back side of the ports when degree'ing to help get an idea of when they open (when you see the light, lol). Gathering a few of these measurements will help in determining if you engine is mechanically mismatched or limited in some way. Just curious, what carb are you using?
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Old 09-13-2016, 04:04 PM
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Thanks for the tips Faded! I really appreciate it. I'm very interested to find out what's going on with it. In the long run it will be good to go through, I just wanted to be riding instead of working on it right now...

I bought a new Keihin PWK 38mm Air Striker, 175 main, 50 pilot and CGK needle in the 3rd position. Stock reed cage with TDR 4 pedal reeds. It starts and idles great, it just lacks power.

Last edited by desertrage; 09-13-2016 at 04:09 PM. Reason: Added carb info
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Old 09-13-2016, 04:12 PM
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like previous replies definately start with these measurements, i suspect something went wrong at the machine shop with the piston/cylinder, also check your top/bottom head/cylinder gaskets to be the correct ones. if you use genuine then don't mind what i've just said but aftermarket ones might be thicker so it drops the compression ratio and alters the port timing. also check piston rings end gaps and piston to cylinder clearances to be within spec and cylinder/head torqued properly during assembly.

btw this engine externally is a piece of art..!
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Old 09-13-2016, 04:24 PM
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Quote:
Originally Posted by desertrage View Post
Thanks for the tips Faded! I really appreciate it. I'm very interested to find out what's going on with it. In the long run it will be good to go through, I just wanted to be riding instead of working on it right now...

I bought a new Keihin PWK 38mm Air Striker, 175 main, 50 pilot and CGK needle in the 3rd position. Stock reed cage with TDR 4 pedal reeds. It starts and idles great, it just lacks power.
Your jetting is way off. I'll get back to you later tonight.
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Old 09-13-2016, 04:52 PM
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Quote:
Originally Posted by byronk View Post
like previous replies definately start with these measurements, i suspect something went wrong at the machine shop with the piston/cylinder, also check your top/bottom head/cylinder gaskets to be the correct ones. if you use genuine then don't mind what i've just said but aftermarket ones might be thicker so it drops the compression ratio and alters the port timing. also check piston rings end gaps and piston to cylinder clearances to be within spec and cylinder/head torqued properly during assembly.

btw this engine externally is a piece of art..!
That's a good thought with the gaskets. Head gasket is a cometic .010" thick, base is an OEM Honda. Ring gap is not looking good, checked with a feeler gage, ring squared up .5" down in bore, gap measures .031"

I have a dial bore gage but not a mic the correct size to set it up for this bore. I'll round one up for a piston to wall clearance check.

All fasteners were torqued per the manual.

Great ideas guys! Much appreciated.

Thanks for the compliments Byronk! I put a lot of effort into the build up. Just need to get it pulling strong.

Faded, Very interested in your thoughts on jetting. I'm at 4200'. Thanks again.
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Old 09-13-2016, 05:02 PM
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Yes, and I'm @ 4700ft, and I don't run anywhere near that rich in my 250's. Assuming everything tight and you're not leaking air a safe starting point would be a 45 pilot, needle on the 2nd clip and a 165 main...and even that is plenty rich.
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Old 09-13-2016, 05:12 PM
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I guess I was confused by the phrase "leak down check" to describe what you did. You're right, I did jump to the conclusion that you may have damaged a freshly built engine but didn't mean to come across
as anything other than bewildered.

Interesting test, did you pump up the combustion chamber through the spark plug hole to check for ring blow by? That's a novel approach though I wouldn't have a clue what an acceptable loss rate is.

A healthy CR500 should be pushing 240 psi on compression test. So the first problem is to find out where all that compression went.

First thing I would do with that big of a number is to check to make sure there isn't something simple like stacked base or head gaskets. Next, cycle the piston and make sure it protrudes a couple of mills
past the cylinder deck when at TDC since you had the crankshaft rebuilt. What kind of work was done to the cylinder head? If you were looking for performance gains, the head should have been altered to
increase compression not lower it. If you have a stock cylinder head handy, installing that and repeating the compression test would be useful info.

Basically, check all the basics first then move to the modifications then whatever's left. Once you get the lack of compression sorted, you can start on getting the jetting dialed in for your altitude - you're
running pretty rich right now.

I'm sure Faded and the others can help get you squared away.
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Old 09-14-2016, 06:34 AM
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if i remember correctly the ring end gap should be within 0.011"-0.020" range new and service limit 0,024".
definitely measure the piston to cylinder gap (normal 0,0027"-0,0041", service 0,005") and squish band.

this might sound silly but, have you installed the piston the correct way with the IN mark towards the intake right? also the piston that you've got is domed or flat top? i suppose the machinist who did the engine work has took into account this, so it can machine the head accordingly to match the piston but you never know, a squish band (use the soldering technique) will clear things up on this.

Last edited by byronk; 09-14-2016 at 06:41 AM.
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