Building a 12.5:1 B20vtec with an overbore. I have some salesman telling me GE states that an 85mm headgasket is ok for an 84.5mm bore. My concern is that I didn't mill the block so it has 2 "low" spots. They are not much but taking away the extra 0.5mm seems to open up the possibility of problems. Any ideas? I think this person doesn't know (or is assuming).

 

it's ok..

 

if you have any "low spots " on the dech of the block, you should take it to a machine shop and have it decked

 

I don't believe that they are low spots. I have to get a straight edge to check the measurements. When I took my block in for bore/hone the machinist noticed a "spot" where the OE headgasket had not seated correctly (in his words). If there is a large discrepency I will take it back to get decked.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PogKai &raquo;</TD></TR><TR><TD CLASS="quote">it's ok..</TD></TR></TABLE>
...and by OK do you mean that it will get me by. I am under the impression that a head seating against a block w/out the .5mm of gasket will leave a void. Compressed gases like voids, and will this lead to premature failure of the gasket?

 

stock HGs come overbored from teh factory, so it can handle an oversized replacement piston w/o needing to stock two different headgaskets, so .5mm is fine

 

Trust me the .5mm bigger bore gasket will be fine I'd be very worried about the low spots you mentioned though,these mls gaskets don't conform like the paper ones w/metal fire rings used in the past they need a perfectly flat smooth surface to seal.

 

Thanks for the responses. I will definetly straight edge the block now. I am trying to upload a pic of the block. What is the current opinion on the use of copper spray??

 

Here is a pic of the cylinder. You can see a burn spot between #2 and #3.

Here's the belly of the beast better known as rotational bling

I am trying to build the motor right so I don't want to sidestep anything. I should just get the block and head decked. I am concerned about the bump in compression. What's the smallest amount that can be removed??

 

Good job man. if concerned please deck it. the comp. bump will be very minimal as they (machine shop) will not mill the deck; they will resurface it this means they will remove the minimal amount of material in order to achieve a perfectly flat surface. Usually they start with about .002 of an inch if that cleans it up then they'll stop. Good luck . I personally like copper spray but only go lightly on the gasket.

 

I know cameras do funny thing to pictures but I would have to have that block decked. It looks like the cylinder is bump downwards on that cylinder. It also looks like its hit the block. Its near the head bolt/stud on the top left hand side