Replaced HG, Now I have Low Compression!

[jdemara]

I'll start out by saying before my head gasket "blew" (slightly), my compression was between 165-170.
It was starting to show symptoms of a BHG (air bubbling out when I take rad cap off, misfiring, running rough...), so I tore it apart and started the HG project.

Had the head machined, new valve seals. Scraped and sanded the block to a smooth surface. Put on a stock "stone" head gasket and torqued it down in 3 passes to 80ft/lbs with ARP studs.

Now I have put everything back together with all new gaskets everywhere, set my cams and crank pulley for the timing etc.

HERE is the problem! I did a compression test on 3 of the cylinders so far, and they are:

#1 - 80 PSI
#5 - 112 PSI
#6 - 90 PSI

I only have done those three cylinders, but, what would cause such low compression after all this work!?

I am sure I have forgot to mention a few things in this thread to make it easy for you guys to help me out. If so, just let me know/ask and I'll provide you as much info as I can.

 

[IJ.]

Check the valve lash.

 

[jdemara]

My machine shop checked it and said it was all within spec. there are numbers writtin on my head where the valve covers go that are like 9, 9, 8, 10, 10 etc...

 

[IJ.]

Again CHECK the valve lash.....

What is it with you guys and this 100% confidence in what the shop tells you..... :nono:

People make mistakes ALL the time.

 

[jdemara]

Ok ok.. so what IF the valve lash is in spec? Then what would I go check.

 

[tlo86]

Again CHECK the valve lash.....

What is it with you guys and this 100% confidence in what the shop tells you..... :nono:

People make mistakes ALL the time.

people lie all of the time too :3d_frown:

 

[jdemara]

so something as simple as valve lash can cause low compression...
nevew knew

im hopoingggggg thats all it is:S

 

[trydrew]

I don't know how much temp makes a difference in a situation like this (i bet Ian does) but was this with the engine cold?

 

[jdemara]

yes. engine cold. it has only ran for about 30 seconds in total with this new head gasket. this was done 100% cold. but still. 80-90!!!! noo way

 

[rumptis]

IJ knows what he is talking about listen to him.

Something else to look at is your timing belt. If you don't have this all setup right the valves would not be closing at the right time and could cause low compression as well.

 

[MK-111]

Did you check the block with a proper straight edge and feeler gauges, after you had scraped and sanded it.
And tbh having the block milled would have been a better idea.

 

[nerfkhat]

Yeah double check valves all my valves were off on mine. My compression was from 90 - 110 because all clearances were too tight.which causes them to open too early and release all the pressure. When I measured first time I mixed up inches and mm measurements.

 

[Zumtizzle]

Yeah double check valves all my valves were off on mine. My compression was from 90 - 110 because all clearances were too tight.which causes them to open too early and release all the pressure. When I measured first time I mixed up inches and mm measurements.

Exactly what i came up with and told him last night.

 

[jdemara]

IJ knows what he is talking about listen to him.

Something else to look at is your timing belt. If you don't have this all setup right the valves would not be closing at the right time and could cause low compression as well.

EXACTLY wut happened! ^^ ALL is good now
i beleive sumhow it was 180 off?!!
but my dad and I went over it watching the cams on each stroke and it was totally off, causing low compression cuz the intake or exhaust would still be open during compression stroke.

Thanks for all your help guys!
Problem solved.

 

[arz]

No offence, but why didnt you use a MHG? After all that work I wouldnt risk a stock type HG. Thats just me though, I hate that job.

Glad to hear all is well. DAMN Metric system!!! LOL.

 

[jdemara]

Tight tight budget at the moment. Just need it running. Going to school soon. I plan to fully rebuild when school is over anyways.

 

[rawmk3]

Umm saying a tight budget is why u didnt use a MHG is kinda a sad excuse. Cause u can get a 1.2mm from HPF for like 100 bux with shipping. So that doesnt seem like a legit reason not to do things correctly. Just my 2 cents.

 

[IJ.]

Umm saying a tight budget is why u didnt use a MHG is kinda a sad excuse. Cause u can get a 1.2mm from HPF for like 100 bux with shipping. So that doesnt seem like a legit reason not to do things correctly. Just my 2 cents.

Add to that the time and $ involved with pulling and stripping the block so it can be surfaced correctly and I can see how it would blow out his budget.

 

[rawmk3]

Add to that the time and $ involved with pulling and stripping the block so it can be surfaced correctly and I can see how it would blow out his budget.

Time i can understand, and I understand tight budgets too, but at the same time, if you own the car, you should really be able to do the correct repairs, and do them the right way. I do agree with you that either he degreed his cams wrong, or he has his valve lash wrong. Maybe the wrong shims in the head on reassembly.

 

[jdemara]

i just said my cams were on the wrong degree.
and owing $3500 dollars already for the last 6 months doesnt help my "budget".

yes, i can say 95% of the time I am a person who does things righ the first time. i totally follow by that saying do it right do it once. but in this case, i have looked into the further costs of doing a mhg and decided im going to wait. and also as mentioned before, i will be rebuilding my whole engine in about a year anyways with brand new everything inside*. so im not too worried about it. it is all stock. not pushing it hard.
and... its not your car so dont worry about it

i do all maintanence myself on this car, and take amazingly good care of it. probably better than a lot of people out there.

anyways thanks for your input guys.