Decompressor Problems... - Honda TRX Forums: Honda TRX 450R Forum

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Old 04-07-2010, 09:38 PM   #1 (permalink)
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I have a '06 450r that is a kickstart model. I tore the motor down recently to install a new set of piston rings. For some reason now I can't hardly get it to start. It is a lot easier to kick over than it was before. I checked cylinder compression with a compression tester and it says 70 PSI. Spec is about 140. My service manual says decompressor clearance should be .010 plus .011 for the right exhaust valve clearance. I adjusted the decompressor clearance all the way to .040 and still can only get about 85 PSI with the trottle wide open.

Does anybody have some tips for me? I'm kinda lost....
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Old 04-07-2010, 10:37 PM   #2 (permalink)
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Quote:
I have a '06 450r that is a kickstart model. I tore the motor down recently to install a new set of piston rings. For some reason now I can't hardly get it to start. It is a lot easier to kick over than it was before. I checked cylinder compression with a compression tester and it says 70 PSI. Spec is about 140. My service manual says decompressor clearance should be .010 plus .011 for the right exhaust valve clearance. I adjusted the decompressor clearance all the way to .040 and still can only get about 85 PSI with the trottle wide open.

Does anybody have some tips for me? I'm kinda lost....[/b]
Your way off try .017
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Old 04-07-2010, 11:43 PM   #3 (permalink)
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the decompressor is only for starting....you will never be able to put a tester on it and read full psi. you would never be able to kick it over if you were fighting that much psi. set it to what the manual says, if its hard to start since you have the valve cover off already double check your intake clearances
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Old 04-08-2010, 12:38 AM   #4 (permalink)
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I understand what you mean, Nathan. By opening up your decomp clearance to .040", you should have BARELY been able to kick her over. Ask anyone who has ever broken a decomp counter weight spring. It is almost impossible to kick over....


As far as your situation, double check your camshaft timing. Hopefully its something simple like that. Maybe a pinched or folded head gasket? I have ruined head gaskets by pinching them on a dowel pin before. Before checking the head gasket, I would do a cylinder leakdown test to help isolate a leak if you do have one.
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Old 04-08-2010, 09:47 AM   #5 (permalink)
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i checked the timing and it is correct. i also have replaced the head gasket and base gasket, along with piston rings thinking they may have been leaking.

This problem has been going on ever since last year when i installed a new OEM cylinder, piston, rings, and gaskets. for some reason after those new, all oem parts were installed, it has just not wanted to start and has not ran as good as it did before.

I am starting to think that maybe the cylinder and/or piston that i installed were either manufactured with some sort of defect, or damaged before they got to me.....? It just seems stange that nothing else changed when i installed those parts and all of a sudden she won't make enough PSI to start correctly......and i have rulled out piston rings and gaskets.....and the decompressor and valves all look good....

what do you guys think?
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Old 04-08-2010, 01:31 PM   #6 (permalink)
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what were your ring end gaps prior to installation?

what was your piston/cyl wall clearances?

these are CRUCIAL for building a reliable / high HP engine....


compression 'can' be bled off via various issues.... valve seating is ONE of them..... so make sure your valves are seated properly and not cupped/damaged.... then there is valve TIMING... make sure your timing chain has not jumped or the possibility of the cam gear FLANGE rotating on the cam itself.... (it happens, just not often).... then the obvious decompressor issue, which you seem familiar with and have already dealt with.... and yes, at .040" gap you should have over 150psi and easily to the point where she would be too stiff to even kick over....

confirming everything MECHANICAL is OK with your lower end? crank and/or rod journal bearings ?? when you last rebuilt it and this issue occurred....what EXACTLY did you replace? piston? rings? cylinder? you mentioned... how about CRANK???? just curious..... you say this has been an on-going issue...so we need to know what occurred when it FIRST showed up.... I assume since your last rebuild she has NEVER had the proper compression???

if so....and your valve train is OK.....your probably correct in assuming the piston and/or cylinder were out of spec..... the ring gaps and piston/cyl clearances will give us this information.....


let us know.....g
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Jetting/N2O: 22N/21F (22hp)

*STU Comp Cut 21x12x8 (6) paddle 'Padla Brats' on Douglas Blue label 8x8.....

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Old 04-08-2010, 08:33 PM   #7 (permalink)
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Quote:
what were your ring end gaps prior to installation?

what was your piston/cyl wall clearances?

these are CRUCIAL for building a reliable / high HP engine....


compression 'can' be bled off via various issues.... valve seating is ONE of them..... so make sure your valves are seated properly and not cupped/damaged.... then there is valve TIMING... make sure your timing chain has not jumped or the possibility of the cam gear FLANGE rotating on the cam itself.... (it happens, just not often).... then the obvious decompressor issue, which you seem familiar with and have already dealt with.... and yes, at .040" gap you should have over 150psi and easily to the point where she would be too stiff to even kick over....

confirming everything MECHANICAL is OK with your lower end? crank and/or rod journal bearings ?? when you last rebuilt it and this issue occurred....what EXACTLY did you replace? piston? rings? cylinder? you mentioned... how about CRANK???? just curious..... you say this has been an on-going issue...so we need to know what occurred when it FIRST showed up.... I assume since your last rebuild she has NEVER had the proper compression???

if so....and your valve train is OK.....your probably correct in assuming the piston and/or cylinder were out of spec..... the ring gaps and piston/cyl clearances will give us this information.....


let us know.....g[/b]
I don't remeber the exact number of the ring gap, but I did check it and it was in spec with what my service manual said.

I do not know what my piston to cylinder clearance was, I did not even check it. I just figured that since both the cylinder and piston were new, OEM parts they would have to be within spec.

As far as valves, I think they should be in great shape. They still have the same shims from when the bike was on the showroom floor. And all of them are still in spec...

I did check the crank for any excessive play when I was inside the motor, and it feels and looks great.

This problem started last year. I tore the motor down to replace the cylinder, piston, rings, pin, and head and base gasket. There was nothing ''wrong'' with any of the parts, I just wanted to make sure that I would have the motor in top shape for the season.

Now before I did this rebuild, she was running GREAT. Starting was easy, always on the first or second kick.

So I installed the new OEM cylinder, new OEM piston/rings/pin (and I checked ring gap) and new OEM gaskets. Finished putting the motor back together and tried to start it... She fired up after about 15 kicks. This is when I first noticed that the kicker was easier to kick. Ran it for a few days like this thinking that maybe the rings needed to seat. Well it never got any better, ran kinda weak and was a pain in the ass to start.

When I just recently I took the motor back apart, I was thinking that maybe I damaged the head gasket or piston rings somehow when I installed them. So I installed new rings, new base gasket and a new head gasket. I reused the same piston and cylinder. This made the problem no better. This is when I adjusted the decompressor to .040'' clearance and still can only get about 85 PSI when kicking it as hard as I can, with throttle wide open.

I bought a Harbor Freight Leak Down Tester. For some reason, I can't get it to give me a reading of how much air leaks out of the combustion chamber. The gauges don't move...... But I CAN'T hear any leaks coming from the exhaust or the intake.... however I CAN hear quite a bit of air coming from the crankcase.....and it makes a gurgling sound too.... I know rings don't seal 100%, but should it be easily noticable with only 15 PSI of air being pumped into the cylinder?
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Old 04-09-2010, 09:59 AM   #8 (permalink)
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i forgot to ask, but how would i know if the cam flange has moved?
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Old 04-09-2010, 11:50 AM   #9 (permalink)
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well....im gonna go out on a limb and say you probably have some type of piston to cylinder wall clearance issue... although usually the ring gaps would be too large as well... so I am a little stumped at that.... but it just seems like the pressure is bleeding into the crank case area.... and it can only do that by passing the piston/rings.... so either you installed the rings incorrectly on two occassions.... OR, there is a mismatch between the piston and cylinder..... I would HOPE you would notice if somehow they sent you an 04/05 piston at 94mm and tried to put this piston into an 06/96mil cylinder... not sure it would even run and the noise would be tremendous.... but still... ya never know....

at some point your going to have to remove the piston and check the clearances.... and just out of curiosity... was there any damage to your old stock jug and piston before you swapped them out? if not, put some new rings on your older piston and re-install with older jug.... I can all but guarantee you that if your machine was maintained at all...the old cylinder is probably in good working condition.....


jmho.....g
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86TRX250R (mostly stock 66mm bore x 72mm stroke) **for sale**
86TRX250R (ESR310 72.5mm bore x 72mm stroke '298cc' fully modded) **SOLD**
88TRX250R (ESR330 77.5mm bore x 74mm stroker '345cc' fully modded)

HRC kit (all but gone)
Hot Cams stage III
Okie porting w/ATP CV4 springs (36mm Ti/31mm)
Venom/KBR N2O Porting w/KW springs (37mm/31mm)
Venom/KBR 487 100mm 14.25:1 piston
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ESR modded intake w/RAT stack
42mm Taper-Bored FCR
Direct Drive clutch lockout, CR500 springs
GT Thunder-Link w/Durablue Lowering Link
Durablue Anti-Sway Bar
Modded shock mounts
Rage Modded Tranny

Jetting/Carb: #168, #45slow, NGPR needle 3rd clip, #55 Leakjet, Pilot 2 turns out.
Jetting/N2O: 22N/21F (22hp)

*STU Comp Cut 21x12x8 (6) paddle 'Padla Brats' on Douglas Blue label 8x8.....

Thanx to: Venom/KBR (Mixxer/Kam), Rage ATV (Dee), Sredum (Chris), and many ORG members
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Old 04-09-2010, 10:12 PM   #10 (permalink)
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Quote:
well....im gonna go out on a limb and say you probably have some type of piston to cylinder wall clearance issue... although usually the ring gaps would be too large as well... so I am a little stumped at that.... but it just seems like the pressure is bleeding into the crank case area.... and it can only do that by passing the piston/rings.... so either you installed the rings incorrectly on two occassions.... OR, there is a mismatch between the piston and cylinder..... I would HOPE you would notice if somehow they sent you an 04/05 piston at 94mm and tried to put this piston into an 06/96mil cylinder... not sure it would even run and the noise would be tremendous.... but still... ya never know....

at some point your going to have to remove the piston and check the clearances.... and just out of curiosity... was there any damage to your old stock jug and piston before you swapped them out? if not, put some new rings on your older piston and re-install with older jug.... I can all but guarantee you that if your machine was maintained at all...the old cylinder is probably in good working condition.....


jmho.....g[/b]
thanks for the tips greg. i am going to try installing the old cylinder and piston this weekend. i'll let you know what i find out.

oh and it is the '06 cylinder and '06 piston..... LOL
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Old 04-11-2010, 07:47 PM   #11 (permalink)
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UPDATE...

i installed the old piston and cylinder today.... and it made no difference at all....

so long story short.... i think that the timing was off by 1 tooth...

but i still can't seem to get the timing marks to line up 100%.... i advanced the chain one tooth, and it makes great PSI when i try to start it now, but the marks are off a little.... take a look at the pics and tell me what you think... is that as close as they get?



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Old 04-11-2010, 08:41 PM   #12 (permalink)
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Are you sure your dead on with the other mark on the crank, sometimes its hard to get a accurate look at it.
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Old 04-11-2010, 10:54 PM   #13 (permalink)
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^ X2 ^....

make sure to get down at EYE level when checking the TDC crank gear mark...

also...your's looks about right BEFORE releasing the chain tensioner...and this will cause the cam gear to rotate slightly clockwise.....plus, you might have a slight KINK in the chain causing it to appear to shorten the chain up.... might wanna think about buying a new chain next time your in there... .they are rather cheap at about $40....

also..you can check TDC using the flywheel... there is an inspection plug for this..... use the 'T' mark... not the 'F'...


jmho....g
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**06 450ER**... #3 (Dale lives on)

86TRX250R (mostly stock 66mm bore x 72mm stroke) **for sale**
86TRX250R (ESR310 72.5mm bore x 72mm stroke '298cc' fully modded) **SOLD**
88TRX250R (ESR330 77.5mm bore x 74mm stroker '345cc' fully modded)

HRC kit (all but gone)
Hot Cams stage III
Okie porting w/ATP CV4 springs (36mm Ti/31mm)
Venom/KBR N2O Porting w/KW springs (37mm/31mm)
Venom/KBR 487 100mm 14.25:1 piston
Cold Fusion Nitrous**
Venom 'QP' pipe
ESR Pro Series pipe
ESR modded intake w/RAT stack
42mm Taper-Bored FCR
Direct Drive clutch lockout, CR500 springs
GT Thunder-Link w/Durablue Lowering Link
Durablue Anti-Sway Bar
Modded shock mounts
Rage Modded Tranny

Jetting/Carb: #168, #45slow, NGPR needle 3rd clip, #55 Leakjet, Pilot 2 turns out.
Jetting/N2O: 22N/21F (22hp)

*STU Comp Cut 21x12x8 (6) paddle 'Padla Brats' on Douglas Blue label 8x8.....

Thanx to: Venom/KBR (Mixxer/Kam), Rage ATV (Dee), Sredum (Chris), and many ORG members
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Old 04-12-2010, 12:50 AM   #14 (permalink)
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Interesting thread. Glad to see its coming along!

Nathan, take some pics of crank gear marks aswell so we can see.

I have run into some bikes where the lines just dont match up 100%, a couple have been 450r's.
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Old 04-12-2010, 01:12 AM   #15 (permalink)
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Quote:
Interesting thread. Glad to see its coming along!

Nathan, take some pics of crank gear marks aswell so we can see.

I have run into some bikes where the lines just dont match up 100%, a couple have been 450r's.[/b]
I will post a pic of the crank punch mark in the morning.

Question for you guys..... I know the cam sprocket has two marks on it.... so.... does it matter which one you look at when you line it up with the triangle/arrow on the cam tower?

And another thing I would like to mention is that when the timing was retarded one tooth, the line on the sprocket was about the same distance from the triangle on the cam tower as in the pic I posted.....just that the line was above the cam tower mark instead of below it....

BTW, the pic in my last post was taken when the chain tensioner was engaged....


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