400ex compression issue

[Gotme1]

whats up people. having issues with my quad, 03 400ex. It wont start since rebuild. Just reassembled my motor with a 426 wiseco piston and new countershaft bearings. had cylinder bored and honed at machine shop and now it is only building 45psi on comp test, got it up to 70 by putting a little oil in the spark plug hole. with brand new rings, piston, bore and hone, i dont see what the problem is. ive pulled it apart twice to inspect cylinder, rings and valve seats and it all looks to be in good working order. Timing is dead on, The only other thing that comes to my mind is that the machine shop didnt do a good bore job or piston is defective. all ring gaps were checked when installed. anything that im missing here guys, im kinda stumped. Any advice is appreciated.

[JOHNDOE83]

Does it run good?

check for oil leaks if it runs?

Maybe your using the wrong adapter for your compression gauge, maybe your compression gauge isnt correct?

Maybe the cam decompressor is throwing it off?

45 psi is way low, maybe its trying to read 145psi?

[dxcody]

Def make sure you adjust your valves.

If they are too tight they will hold the valves open and when your turning it over the compression will shoot right out instead of building up.

I have done that many times.

[dxcody]

Oh also, you are holding the throttle wide open when you are doing the comp test right?

[Gotme1]

it hasnt ran since rebuild. valves are adjusted to specs, and i hold throttle open while testing it, I am using the right adapter for the compression gauge also. I am running out of thoughts. ive rebuilt this motor before with no problems. The only thing thats different now is piston size with fresh bore. the decompression plunger is in as well as the spring. the starter is just turning over the motor quicker than normal which makes sense because there is not enough compression to actually put a load on the starter. ima tear back into it tomorrow and if i cant figure it out im gonna take the cylinder back to the machine shop to make sure every thing is good. really appreciate the help guys, Any opinions are greatly appreciated. Need to get this thing back running

[Gotme1]

ok. finally got to do a leak down test. the compression is leaking past the rings. felt the air coming out of the timing plugs on side of motor. i followed the directions for the wiseco piston for the ring placement and all gaps were checked and correctly positioned. does anyone know what the piston to wall clearance should be? would it be oem clearance with the wiseco piston. oh and its 10:8:1 comp

[Gotme1]

i was able to get a .008 feeler gauge between the piston and cylinder wall, Does that sound about right? ive looked all through the directions that came with piston and saw nothing that stated the p2w clearance

[CJM]

Im not sure the exact specs, but to me it sounds as if they bored the sleeve too much.

Look at it like this: I had a worn sleeve and put new rings in, the piston plopped right in no problem. I could clearly see there was a small gap between piston and sleeve wall even with rings. After having it together it didnt run right. I went up another piston size and had it bored. It was MUCH harder to get that piston to go into the sleeve.

You have too much clearance. Whomever did the bore job messed up.

What size does the piston measure? Should be 88mm for a 426 if I recall-or close at least.

[Gotme1]

piston measures 88mm. I am measuring .008 clearance which i personally thing is a little too much. Im going to talk to machine shop today and see if i can take it back to get cylinder clearances checked. We will see what they do for me because im sure that is the problem. Everything else checked out good so that is my last resort. keep my fingers crossed and hope that they reimburst me for boring my cylinder to big. Ill keep yall updated. Thanks again guys

[chronicsmoke]

Did they bore the cylinder to match the piston or did they just bore it to whatever number they figured you would need?

[Gotme1]

yes. cylinder was dropped off at machine shop with piston so it is bored to fit piston. I just cant seem to find the p2w clearance. OEM clearance is .002, service limit is .004, i was able to fit a .008 feeler gauge, so if thats the case then they bored way over. ive also read that wiseco piston should have .014 clearance. Can anyone confirm that for me? need to know because im taking cylinder back to machine shop today at lunch and i need to know what kind of clearances i need so i can argue for a reimbustment if they jacked my cylinder up. Thanks guys

[Gotme1]

Update from machine shop. they checked the p2w clearance and told me it was .003, what do you guys think? Service limit is at .004, it calls to be bored with .002, im already half way there with his overbore. His reasoning was that high performance/high compression motors are always bored with a little bit more clearance versus oem setup. does that sound right? And i dont believe .001 of an inch would kill my compression, correct me if im wrong.

[Stickman400]

I'm no engine expert, but I have done my own rebuild on my 400, and that doesn't sound right to me. You would think you want it to be the same as or slightly tighter tolerances than OEM.

[Gotme1]

alright guys, we got it narrowed down. when he bored the cylinder, he didnt compensate for the thinner cylinder wall at the bottom of cylinder, So when he was running the bore through it the thinner part of cylinder got much hotter than the rest, When it cooled off it expanded even more. so cylinder is trash. He offered to buy me a new stock cylinder, or a sleeve to drop in, and he is gonna disassemble head and clean it for the troubles. Ill be ordering a sleeve today. Any reccomendations? I was leaning towards la sleeve. and does anyone sell a 87mm?

[Stickman400]

LA Sleeve is a great choice, can't go wrong with them. And you can't buy an 87mm sleeve as far as I know. Your just going to have too buy a stock size sleeve and have them bore it, again.

[Stickman400]

Here's what you need: http://www.lasleeve.cc/index.cfm?event=product.display&product_ID=949

[dxcody]

Get on ebay and buy the entire new cylinder. You can buy them in 87mm and its only $200

[Skerry1]

You said you had a 426 piston, I'm new to all this but I believe the 87mm is for a 416. Wouldn't you need an 88mm Cylinder/Sleeve?

[Gotme1]

thanks sickman. that will prolly be the sleeve i go with. i have also looked at the cylinders, id rather go with a sleeve jus for peice of mind, and plus it will be the cheaper route because im not paying for any machine work. And about the 426, your right about it being 88mm, but i need a 87mm so i can get the sleeve bored to the correct clearances for the 88mm piston.

[Gotme1]

Anyone know where to get a head gasket for the 426, I had the stock head gasket but since I have it apart I want to order a thinner steel layer gasket just cant find on for 88mm

[CJM]

Cometic brand gaskets. Just make sure its listed as an MLS type gasket.

You can use the stock size on anything except a 440.