Vitos big bore compression

[abner99]

I just rebuilt everything new piston new rings new bottom end Machined cylinder so no scratches or anything it's all brand new. I just did a compression test and I got like 110 or just below 120 and this can't be right can it. Help please

 

[Awk08]

i don't believe the bbk kits have any higher compression than a standard top end. which should be in the 120 - 130 psi range after break-in and the rings seat themselves.
did you hold the throttle wide open and kick it until the needle stopped moving ?
was it leakdown tested ?

 

[abner99]

Yeah I held the throttle wide open and waited for the needle to stop but my kick start was sliping could that be it. No leak down was tested anarobic was used on all gaskets

 

[Larry's Shee]

Didn't answer if it was broke in yet. That would make some difference. What type of gage you using? That also makes a difference, adapter has to be same length as plug, shorter ones= 5lbs less. Where is schrader valve on it?

 

[Blaaster]

Yeah I held the throttle wide open and waited for the needle to stop but my kick start was sliping could that be it. No leak down was tested anarobic was used on all gaskets

Fresh rebuilds can be very low in compression until the rings seat during break in.

If the motor has not been started yet, compressions can vary depending on how much 2 stroke oil was applied to the rings during fit up.

Did you put goop on the head gasket, it should be fitted dry.

 

[best]

What is your squish distance?
This is very important and should be about 1mm, or 0.040" give or take 20%.

Steve

 

[abner99]

no its not broke it in hasent even been started using a us general gauge and i put the fitting in that fit the threads also i put some not alot of anaerobic sealant on the head gasket and tightened to specs. what is a squish distance and what valve

 

[Larry's Shee]

Schrader valve is like a tire valve stem. If it isn't at very end then you have volume of hose/adapter to compress. Tho with 120# you should be good. Also extreme ex porting can give lower numbers.

 

[abner99]

Thanks Larry but there's no schrader valve and like its just below 120 and what so you mean extreme porting

 

[Blaaster]

no its not broke it in hasent even been started using a us general gauge and i put the fitting in that fit the threads also i put some not alot of anaerobic sealant on the head gasket and tightened to specs. what is a squish distance and what valve

Copper head gaskets should be installed with no sealant.

It is very possible that when you tighten the bolts after heat cycles the dried sealant will fail causing a leakage.

Re tensioning of any surfaces which have anerobic sealant on them should be avoided, as the surfaces will have been void of any air and the sealant would have cured.

 

[mud runner]

sounds like you need to leak test and put a new head gasket on

 

[Larry's Shee]

Extreme exhaust porting would be like drag racing, maybe dune. What is , is that the ex port is open longer, thus having less port closed cylinder area to actually compress the charge. This would be the "corrected compression ratio". I don't think you have any problems with the cylinder, however I wonder why you put sealer on head gasket?

 

[Blaaster]

Extreme exhaust porting would be like drag racing, maybe dune. What is , is that the ex port is open longer, thus having less port closed cylinder area to actually compress the charge. This would be the "corrected compression ratio". I don't think you have any problems with the cylinder, however I wonder why you put sealer on head gasket?

Especially one that sets hard with the absence of air.

 

[abner99]

Yeah but I didn't glop in on I took my finger and smeared it so it was just a better seal or stick

 

[abner99]

Yeah it's Anarobic so it really should do any harm

 

[Blaaster]

When the solid copper gasket becomes conditioned and it comes time to re tension after the heat cycles.

Good luck.

 

[abner99]

So what are you saying conditioning and re tension

 

[Blaaster]

A fresh rebuild requires 3 to 5 heat cycles to start bedding in the rings and to condition the gaskets to expansion and contraction.

The head and jug bolts must be then re tensioned to ensure a perfect seal.

 

[abner99]

Gotcha thats good to know so my head gasket for now should be good I don't need to replace then

 

[Blaaster]

Gotcha thats good to know so my head gasket for now should be good I don't need to replace then

The problem as I see it, is by using a sealant which will set hard between the copper gasket and the top of the cylinder, and between the gasket and the head, when the head is re tensioned the copper gasket will be compressed a little and may cause the hardened sealant to be disturbed an loose sealing properties.

A soft copper gasket needs no sealant applied, the copper will compress enough to fill all the blemishes.

After you have done the heat cycles, retensioned the head and jug, and after warm up, take it for a gentle ride for a few miles.

Now do another leak test paying particular attention to the head gasket area with soapy water.

You may just jag it and no leaks will show up.