Relieved exhaust bridge and other 01 mortor questions

[kdizzle]

I have a 01 that has over 80 hrs ont he top end. I took it apart for fear or grenading and found a PRO-X in there that seemed to be aok. I am having the bore measured but have immediately noticed there is no relief or scallops on the exhaust bridge. The bore looks ok, some minor scuffing at the bottom of the bore which cleaned up easily with some fine grit sandpaper. the bore looks good now, but it still needs to be measured.

questions i have:

if i am slapping another prox in there do i need the bridge relief? is there any pictures of a properly relieved bridge i can reference? i have searched the forums hight and low.

what is the stock bore supposed to be? 89.5? i have a shop manual on the way (btw).

I have a complete 86 motor on my bench. Can i directly bold the head onto this 01 motor for a boost of compression as i have read? is this a direct bolt on? or does any modification need to be done to the head or piston? roughly what kind of compression will i have then? will i need race gas at that point?


Previosly the steel beast was relatively easy to start and ran like a champ the entire 2008. i beat it hard and it always came back for more. It runs 32:1 927 and shell vpower always. This engine will find its new home in a 04 450 AF hence the refreshing. just need a strong and reliable motor for MX and sand. Thanks

[MICK]

Bridge should be clearanced .002 - .004". The bridge relief is in addition to the piston to cylinder wall clearance. Make sense? Turns out to be around .006" piston to bridge. Relieve the bridge
The two scallops would be ontop of the exhuast port. If you have an 89.5 or larger bore there is a good chance they've simply been bored out. Stock is just 89mm.

I don't know anything about older model CR500s. Your fuel and oil choices are good. And most of all good luck with your AF build

[97af]

questions i have:

is there any pictures of a properly relieved bridge i can reference? i have searched the forums hight and low.

:

The search is over.............

[100hp honda]

I have a 01 that has over 80 hrs ont he top end. I took it apart for fear or grenading and found a PRO-X in there that seemed to be aok. I am having the bore measured but have immediately noticed there is no relief or scallops on the exhaust bridge. The bore looks ok, some minor scuffing at the bottom of the bore which cleaned up easily with some fine grit sandpaper. the bore looks good now, but it still needs to be measured.

my scallops were gone at .040 so you might be .040+

questions i have:

if i am slapping another prox in there do i need the bridge relief? is there any pictures of a properly relieved bridge i can reference? i have searched the forums hight and low.

if you relief the bridge is up to you. some may argue against it for cast piston but either way this is how honda does it.

what is the stock bore supposed to be? 89.5? i have a shop manual on the way (btw).

89

I have a complete 86 motor on my bench. Can i directly bold the head onto this 01 motor for a boost of compression as i have read? is this a direct bolt on? or does any modification need to be done to the head or piston? roughly what kind of compression will i have then? will i need race gas at that point?

i think all the heads interchange, but im unsure the dome cc. newer bikes were 6.8:1, '87 motors were advertised at 7.4:1. cylinder pressure is easy to find with a gauge if thats what your looking for. however if you want trapped compression ratio (ratio between cylinder volumes when exhaust closes and volume when piston is TDC) :

CR=

(V1+V2)
---------
(V2)

CR= compression ratio
V1= cylinder volume at exhaust closing
V2= combustion chamber volume

or traditional compression ratio:

CR=

(V1+V2)
---------
(V2)


CR= compression ratio
V1= combustion chamber
volume plus piston
displacement from
TDC to BDC
V2= combustion chamber
volume

i can give you my input on how i think of this. i think my bike lost compression because i raised the exhaust, but i didnt shave down the head enough. i think i need to shave more off the head to get alot of compression back. maek sense ?

Previosly the steel beast was relatively easy to start and ran like a champ the entire 2008. i beat it hard and it always came back for more. It runs 32:1 927 and shell vpower always. This engine will find its new home in a 04 450 AF hence the refreshing. just need a strong and reliable motor for MX and sand. Thanks

[AlisoBob]

[100hp honda]

good post bob. i got alot of books people would be interested seeing but i dont know how to post pdf ?

[AlisoBob]

Its not a pdf, just a photo of a page.

[Roostius_Maximus]

the head is deffinately tighter compression, you could try it and see what it works like for you. oem or cometic base gasket? have you checked to see where the piston sits compared to the top of the jug?

[kdizzle]

Thank you guys for the great information, the pics and pages were exactly what i am looking for. I will relieve the bridge for safety sake, The bike will be operating in the AZ desert and most definately will see some airtime out at glamis DO the scallops really make it that much easier to start? does it not sacrafice compression? It was never terribly hard to start without them, well at least no harder than any 500 ive started in the past.

However, The Prox held up really well for me, and am thinking about installing another.. ahh the great debate between cast vs. forged..

today my MPS frame will be ariving, have some nice parts to assemble it with. I need to get some pics up for you guys. I have never ridden an AF but have had an 86, 87 (both put me in the hospital lol) and 93 steel beast. I now have an 01 steelie and will be upgrading to an 04 AF.. guess i have a love for the 500 glad i am amongst like minded people here .. Cheers to the 5

[dannygraves]

you can use an '86 head if you use the '85-'88 head gasket. its 2mm thicker, or your compression will eb way too high and she will knock and ping all over. I'm running an '86 head on my '90 motor useing an '86 head gasket.

[AlisoBob]

1.I will relieve the bridge for safety sake,

2.DO the scallops really make it that much easier to start? does it not sacrafice compression?

3.ahh the great debate between cast vs. forged..

1. Position the ring over the bridge.... it you can see light betwen it, your good to go.

2. Scallops can be reground in. Once the motor is running, compression is the same.

3. I like cast....

[dannygraves]

to answer #2 my gen-4 still has scallops and even with the 7:1 compression on the '86 head, I can still start her sitting down with a freash topend, couldn't even dream of doing that on my gen-1.

[mega491]

Fellow Hoons,
My Gen III w/91 CR 500 power is the hardest starting beast I have owned as far as BIG compression. I completely rebuilt the entire engine assembly prior to installing in the frame. The scallops are gone due to overbore. I wear knee braces and cannot start it on flat ground since the brace prevents my knee from bending enough to get on the top of the kicker since it will not start without a full hard kick from the absolute top of the travel of the kicker. I have to find a berm or something to stand on with my left foot if I stall out on the track to get it started. I've got 490 Maicos and a 1984 CR 500 with a short little kickarms that are waaay easier to start than my beer can.

My question to you guys is: is it worth the time and effort to dis-assemble and cut-in the scallops?

[AlisoBob]

If I wore braces... I would do it for sure....

[iggys-amsoil]

My question to you guys is: is it worth the time and effort to dis-assemble and cut-in the scallops?

No. Once there gone, be done with them.

I'm not in your knees and /or braces however it sounds like the bike isn't beening kicked over at TDC. The discription sounds like a big guy relieing on pure weight and length of stoke in hopes of it firing?

[sabreguy]

Fellow Hoons,
My Gen III w/91 CR 500 power is the hardest starting beast I have owned as far as BIG compression. I completely rebuilt the entire engine assembly prior to installing in the frame. The scallops are gone due to overbore. I wear knee braces and cannot start it on flat ground since the brace prevents my knee from bending enough to get on the top of the kicker since it will not start without a full hard kick from the absolute top of the travel of the kicker. I have to find a berm or something to stand on with my left foot if I stall out on the track to get it started. I've got 490 Maicos and a 1984 CR 500 with a short little kickarms that are waaay easier to start than my beer can.

My question to you guys is: is it worth the time and effort to dis-assemble and cut-in the scallops?

Sounds to me like you should be thinking............................
Decompression lever!

[mega491]

Have tried from TDC and rotating just past TDC and either way it takes a full hard kick to start. I'm only 5'11" tall but weigh 220, longer legs would help but that's not an option. Bob, you posted above once the engine starts the compression is not effected by the scallops. I assume then that off idle I will still have the same throttle response and overall performance I have presently after cutting in the scallops?

I want to add that I have installed 1996 CR 250 ignition, flywheel and all. Due to the smaller and lighter flywheel could this be some of the reason for this? I installed the 250 ignition when I rebuilt the engine. So I cannot compare to stock starting. I have not had a 90 or newer CR 500 in the last 10 years and that one was a Gen I with an 90 CR 5 but had stock ignition (scallops were non-existent as well) and it was not this hard to start.

Are there different thicknesses of base and or head gaskets for different years and could I have installed a wrong gasket? It has a steel shim type head gasket and the base gasket didn't seem any thicker that around .5mm +or-.

[aloha450x]

im at 89.25 on a oem oversize piston. scallops are still there and bridge relieved. I also an runnind a cr250 kicker with roostmaximus decomp. I can sissy kick it and she fires over. without the decomp I can start it fairly easily and always first kick. I can stand on the kicker without it moving. haha my little ass. I suggest for you old busted farts haha to get a decomp from adam!!!! and there is something to be said for spot on jetting (thanks danny) I was one size pilot fat and one size main lean.

[mega491]

Thanks for reminding me of the fact that I am getting old and am busted up. I guess it possible 10 years ago the knees worked better and the 5 started the same.....

Who is Adam, where is he located and how much will he charge a Hoon for a decompressor install?

[Roostius_Maximus]

just barely sent you a PM about it, I'm in Winkler, Manitoba, Canada.

[aloha450x]

just poking atcha. haha I had 2 acl reconstructions on the same knee. luckly it was on my left. im good aslong as I don't buy ktm. haha as far as the decomp it is silly esy to kick. look in the pics and vids to see my wife starting my 500. it is hard findint tdc cause the stroke is so light. seriously. if I had to compare it to a bike I would say its like starting a cr250.

[Roostius_Maximus]

Gen3 CR250 valve access

[mega491]

Adam, That's perfect as far as location. I am going to dig through some boxes and see if I can find an extra head to send for the decompressor install.

[Apollo]

From what I have been reading about CR250 ignitions lately, maybe it is the lighter flywheel weight of the 250 that is making it hard to start.

[Roostius_Maximus]

the 250 flywheel takes away inertia, its still the compression thats making resistance