Engine Compression #'s

[fireburns99]

Just have a quick question regarding engine compression and head gaskets. What kind of compression is normal for a stock engine, with stock head gasket? And then for comparison purposes what is the compression when using a cr, versus, splitting the stock head gasket?

I'm just looking for some data points, as right now i'm seeing 210-215 when using the the thin piece of the stock head gasket, on an 86 engine. With the cr head gasket before I was seeing 180-190, just curious if this is anyone elses experience.

Thanks for the input guys.

[Honda 250r 001]

if i were you i would not use the thin piece of a stock head gasket, im sure it will leak. I would take both thin pieces off and run the middle thick one.

Anywho stock comperssion is 175 give er take 5 psi i believe i read a while back.

[86 Quad R]

Originally posted by Honda 250r 001
if i were you i would not use the thin piece of a stock head gasket, im sure it will leak. I would take both thin pieces off and run the middle thick one.

Anywho stock comperssion is 175 give er take 5 psi i believe i read a while back.

ur thinking is just the opposite...... the thinner have the defined raised areas that aid in sealing whereas the center does not. i've been using the same thin gasket going on twelve years, repeadily....

the stock compression can vary anywhere from 145-175 simply because of the varying deck hieghts from cylinder to cylinder. over the years i've measure virgin oem cylinders that varied from .065 - .125 in deck to piston. :cool:

[zedicus00]

yeah do not run just the middle piece. either use the complete gasket or one of the thin pieces. the cr250 gasket is identical to using one thin piece.

lowest stock compression on an R i have ever seen was about 160, but even at that i did a rebuild. i shoot for 180-200. any more then that and you have to run race gas. (200 is on the brink, do some testing)

[fireburns99]

Originally posted by zedicus00
yeah do not run just the middle piece. either use the complete gasket or one of the thin pieces. the cr250 gasket is identical to using one thin piece.

lowest stock compression on an R i have ever seen was about 160, but even at that i did a rebuild. i shoot for 180-200. any more then that and you have to run race gas. (200 is on the brink, do some testing)

Thanks for the replies guys!

Zed, how do you achieve the 180-200 compression. Using one thing piece of the gasket puts me at 210-215! And that also includes some thickness for the 1211 sealant. When i tore the engine down before this rebuild it was at 200 or so and that was with a cr gasket.

Thanks for your help.

[Honda 250r 001]

Originally posted by fireburns99
Thanks for the replies guys!

Zed, how do you achieve the 180-200 compression. Using one thing piece of the gasket puts me at 210-215! And that also includes some thickness for the 1211 sealant. When i tore the engine down before this rebuild it was at 200 or so and that was with a cr gasket.

Thanks for your help.

85 atc head gasket, what does that give you?

[zedicus00]

Originally posted by Honda 250r 001
85 atc head gasket, what does that give you?

yup, they are a different thickness yet so try it.

also you can stack some cylinder base gaskets. maybe 3, i wouldnt go more then that though.

[mcboomport]

Originally posted by Honda 250r 001
if i were you i would not use the thin piece of a stock head gasket, im sure it will leak. I would take both thin pieces off and run the middle thick one.

Anywho stock comperssion is 175 give er take 5 psi i believe i read a while back.

I can not believe you are giving this guy advice. Wow, that would have been a shame if he listened to you. You should probably know what you are talking about if you are giving that kind of advice!

[zedicus00]

Originally posted by mcboomport
I can not believe you are giving this guy advice. Wow, that would have been a shame if he listened to you. You should probably know what you are talking about if you are giving that kind of advice!

normally i dont make these posts, but that really wasnt necessary.

[IcutMetl]

According to the Honda factory service manual, stock compression is 180psi +/- 15psi.

Mine was at 155psi when I first tore into it. I found that the previous owner did infact have it bored .020 over, but was only using a .010 over Wiseco piston.

I used a thin portion of the stock head gasket, coated it with copper spray, and with a .060 over piston I achieved 195-200psi of compression cold. Stock base gasket setup and did have it ported as well when it was apart. This is on an '88 motor.

[woodsracer144]

Originally posted by mcboomport
I can not believe you are giving this guy advice. Wow, that would have been a shame if he listened to you. You should probably know what you are talking about if you are giving that kind of advice!

it should still seal up... even if he did, the guy was gonna just run the thin part... one way or another if he would have done the work and checked compression and did a leak down test he would know if it was all sealing...

[fireburns99]

Thanks for the info guys. I wanted this thread to more informational, than implying that I am going to modify my head setup. I just wanted to see what numbers people are getting with what setup, so that if I or anyone else for that matter are looking for a particular compression number, than they'll have a starting point.

[86 Quad R]

.... as you've noticed. the compression can vary a great deal from engine to engine using same "everything" and that is largely due to the varying deck heights of the oem cylinders(and head volumes) that rolled off of the assembly line from honda.:ermm: i'm quite certain that the same will hold true with any of the aftermarket variety aswell. ;)

[Honda 250r 001]

Originally posted by woodsracer144
it should still seal up... even if he did, the guy was gonna just run the thin part... one way or another if he would have done the work and checked compression and did a leak down test he would know if it was all sealing...

damn i just cant believe that those thin piece would be enough to make something seal. I have trouble with the full gaskets with he raised ribs to smash let alone just one thin piece.

[fireburns99]

Well typically when we run the thin portion we use 1211 3 bond sealant to help seal the head... But think of it this way, if you use the thick gaskets it a flat machined piece of sheet metal right? Well the thin pieces have the ribs that ultimately flatten to seal all irregularities in the head/cylinder. That's why the stock gasket has one on each side of the thick piece.

With that being said, I am surprised to hear that people have had success with re-using them over and over. I have typically been just buying stock head gaskets and getting two rebuilds out of them (use one thin piece each rebuild).

[86 Quad R]

Originally posted by fireburns99
Well typically when we run the thin portion we use 1211 3 bond sealant to help seal the head... But think of it this way, if you use the thick gaskets it a flat machined piece of sheet metal right? Well the thin pieces have the ribs that ultimately flatten to seal all irregularities in the head/cylinder. That's why the stock gasket has one on each side of the thick piece.

With that being said, I am surprised to hear that people have had success with re-using them over and over. I have typically been just buying stock head gaskets and getting two rebuilds out of them (use one thin piece each rebuild).

lol i've used mine so much that over the years it's went from .010 to .008 from the repeated cleaning with scotch brite/carb cleaner. :cool:

[troybilt]

Hey gentlemen, I'll try not to sound like a complete boob here but... well here we go... I'm rebuilding my topend today, just got the cylinder back from the machineshop and see you are using some sort of bond or spray sealant on the head gasket, when using the thin portion of OEM gasket or a new CR type gasket, 1211 3 bond, or copper spray. Is this stuff found like at Oreilly's or something? Do you use anything on the bottom to help seal?

[IcutMetl]

The stuff I used is made by Permatex and comes in a 9oz. can. You won't use much, just enough to coat both sides of the gasket and let dry- it should last you for about a hundred thousand rebuilds. I didn't use anything but the gasket itself on the base. I bought my can at AutoZone.

[troybilt]

Awesome, Thanks. That's what I thought, but wanted to be sure.

[86 Quad R]

for best overall results i'd recommend using the three bond. :cool:

[C-LEIGH RACING]

Originally posted by 86 Quad R
for best overall results i'd recommend using the three bond. :cool:

I'll 100Xs that.
Three Bond # 1211 sealant will seal a warpped head, long as you give it plenty of time to cure out.
It can be hard to find that product though, I get mine from a wholesale aftermarket supplier out of Little Rock, Ark.
1211 will run around 20 bucks for the tube.
Neil

[troybilt]

I went with the copper stuff. If I have troubles, I may be on the hunt for the 3 bond stuff.

Thanks,
Troy

[troybilt]

I'll check compression once I get the motor back in the bike, but what would you guess the compression would be on a stock 0.010 motor Wiseco piston, stock head with the thin portion of OEM gasket? I actually used a new Cometic gasket, but looks the same as one of the thin portions of the OEM. I'm guess numbers near the 190's in psi. Would I be far off?

[troybilt]

One more question. When running the single thin portion of the head gasket, (basically what all you get from Cometic), do you need to run 2 base gaskets? A buddy was told this from Cal-ATV that when running the CR head gasket, (I assume is similar to the thin portion of OEM), that 2 base gaskets must be run. quote... "or you'll burn up the piston..." from Cal-ATV. Any truth to this at all?

[86 Quad R]

yes and no. you may recall in past posts regarding this very subject. these R cylinders have such a variance in deck hieghts(top of piston to cylinder deck) that you may or may not end up with a compression that too high for pump gas. i've seen them(deck hieghts) vary from .060" - .125" but to say that "all" engines should be run with doubled when using the thin head gasket is a safe way to CYOA on cals part. :cool:

[troybilt]

I think I understand on the compression #'s and had planned to check once the motor is back in the bike and if said compression is too high, I will use race gas, not super worried about that.. if its just compression they were meaning...

My question really stemmed from this, (i should have mentioned before), they also claimed that the extra base gasket changes the porting by moving the ports up basically (no sure how far, 0.01" maybe?)... I don't know what this does to the performance good or bad, but I could see how that would be effected, and I was concerned that this may cause adverse effects. Any thoughts on this? I built the motor with a single base gasket and wasn't planning on changing... I just thought that was interesting.

I'm not a newb here and realize this may have already been discussed... I did a few searches and nothing came up with any relevance in my intial results.