decompression problems

[sweet t-rex 400]

new here and thanks ahead of time for help. I got 02 400ex...tore it down for a head gasket and when i put it back together I lost the spring for the plunger in the head that works the decompression mechanism. It is a stock cam i believe cause the aftermarkets don't use this mechanism. I have heard on here you can remove the mechanism from the stock cam and remove the spring and plunger from the head...it will run good. I did this and still wont run. VERY MAD!!! I'm just burned out from this problem. I've triple check the timing and valves...there good. It's getting spark and fuel also...just wont fire. So...the question is...can I remove the decompression mechanism from a STOCK cam and it will run? Why does the aftermarket cams run without it? Are the lobes offset a little to open the exhaust valve or something? Please any help would be greatly appreciated.

[400exrip]

No, That is what my 400ex was doing a while back when I rebuilt the motor and forgot to put the decomp plunger and spring back in and it would not ever crank up, Put that back in and it ran great.

Now If you are running a Hotcam you will want to remove the spring and plunger always, If you look at a Hotcam and your Stock cam side by side, you will see this extra material by the cam flange on the stock cam, this will not be there on the Hotcam. All of this is the Decompression Assembly a Hotcam does not use this so if you ever get one, remove the spring and the plunger.

Her are some part Numbers

Spring, 14126-KV2-940

Plunger, 14125-KV2-940

[sweet t-rex 400]

i already removed the decompression mechanism from the cam...I'm very impatient. I know with a stock cam you should leave everything how it is...thats what it is there for. What should i do...buy a new mechanism and put it back to factory? And also why does the aftermarket ones run without this set-up?

[Stickman400]

Hotcams and most other aftermarket cams dont use the decompression mechanism. If it is stock and you want to run it without that in there, you have to take the cam and press off the decompression mechanism off the cam itself and then weld shut the oil holes. Theres a member on here who did it, maybe he'll help you out more.

[400exrip]

I accedently posted the part numbers in my first post they are up there at the top.

[dxcody]

you can tig weld the holes in the stock cam and then grind and smooth them down so the stock cam will work without the decompression mechanism. There is a thread on here that i saw it on, if i remember correctly.

Note: I am not talking about the holes on the cam lobes, i am talking about the 2 holes that are underneith the decompression mechanism once you remove it.

[sweet t-rex 400]

what does welding the holes in do though...I dont wanna weld them up then have it still not work and have to buy a new cam. I would like a little more info before i do that. how does the aftermarket ones run without it? how does the motor release compression without it? thanks

[CJM]

Im not going to get into the specifics here with this, all Img oing to say is pick a # you like:
1. Buy an aftermarket cam, the stock cam sucks anyways. Hotcam Stage 1 is what you need.

2. Fiddle around with the stock cam, the amount of work you need to do to get it right is not worth it

3. Buy the plunger and spring.

Dont need the decomp mechanism, no idea why it even has one.

[DirtyBirdRacing]

Originally posted by CJM
Im not going to get into the specifics here with this, all Img oing to say is pick a # you like:
1. Buy an aftermarket cam, the stock cam sucks anyways. Hotcam Stage 1 is what you need.

2. Fiddle around with the stock cam, the amount of work you need to do to get it right is not worth it

3. Buy the plunger and spring.

Dont need the decomp mechanism, no idea why it even has one.

I would go with #1 I was thinking of saying go with a HC when i was reading things about welding it :huh :huh

Link to HC http://www.hotcamsinc.com/ProductInfo.aspx?item_id=9

[dxcody]

Originally posted by sweet t-rex 400
what does welding the holes in do though...I dont wanna weld them up then have it still not work and have to buy a new cam. I would like a little more info before i do that. how does the aftermarket ones run without it? how does the motor release compression without it? thanks

it has something to do with the oil flow i believe. I would just buy a HC tho. $130 on ebay and it makes a world of difference.

[sweet t-rex 400]

I bought the spring and plunger for the head and gonna put the decompression mechanism back on the cam...put it back to factory for now. Want to put a big bore kit and stage 3 hot cam in this winter and don't wanna buy a stage one now and waste money. Thanks to everybody though and I know a lot more now about the stupid factory cam. I just cant believe it wont start without that little spring...its crazy!!!

[CJM]

Stupid design imho, reason why all the aftermarket cams eliminated it.

Enjoy your build up when you do it, once you go big you wont go back.

[dxcody]

Originally posted by CJM
Stupid design imho, reason why all the aftermarket cams eliminated it.

Enjoy your build up when you do it, once you go big you wont go back.

Very true, once you go big you will never be satisfied again with a stock 400

Hope that solves all your problems! :D

[sweet t-rex 400]

got all my parts in and hope to get it back together tomorrow. If it goes good im headed for busco beach saturday...crossing my fingers!!!