Where's my Compression??

[7mgte1988]

Listen guys ive done a little rebuild as one of my valve seats fell on to the vavle but to make a long storie short.. I did a compression test before the rebuild and it can back good as of one cylinder(5) at 96 but the rest are in the mid 120's... I resurfaced the head, checked the valves and put mineral oil on top of the pistons to see if the rings were bad they all held the oil..As i was near the end of the rebuild i decided to do a compression test and I only tested 4,5,6 and they all had mid 90's :1zhelp:
Could this be timing?? 180over... And i did put Cylinder num1 TDC on compression stroke before i started..I did have a metal head gasket at 75lbs without the copper spray.

I would like to get you guys opinnion on what this could be..

 

[thorpedo]

Mineral oil on top of your pistons won't tell you if the rings are sealing properly. Whoever told you that is rather joking or should not be working on engines.

It could be timing, but it could be many thing.

List everything you did / had done to the engine during your "rebuild" and we will be more help.

 

[hvyman]

if you do a comp test and one is low and then put a little motor oil in(like a teaspoon or less) and the comp raises then its the rings.

 

[lewis15498]

Mineral oil on top of your pistons won't tell you if the rings are sealing properly. Whoever told you that is rather joking or should not be working on engines.

Incorrect. Usually use motor oil but this does work. The oil helps bad rings form a seal, reducing blowby and raising compression.

Do a comp test on all cylinders. This should be with all of the plugs out and throttle wide open. To check your timing slide a long wooden dowel into cylinder #1 spark plug hole so it is resting on the piston. Slowly crank the engine over manually and watch the dowel travel. When the dowel reaches its highest point that is TDC. Check to make sure that the timing mark on the main pull lines up with the 0* mark on the timing cover. If it doesnt, the damper slipped. If it does then ensure the two cam marks are pointing straight up. If they are pointing straight down. turning the engine 360* will put them straight up. If they are not then your timing is off. Finally make sure that the alignment pin on the cam is in the middle of the three holes on each cam gear. If all these things check out, valve timing is not your issue.
If the teaspoon of oil test boosts your compression, then you probably need rings. My initial guess however is your MHG did not seal properly because you did not resurface the block.

 

[thorpedo]

Incorrect. Usually use motor oil but this does work. The oil helps bad rings form a seal, reducing blowby and raising compression.

Do a comp test on all cylinders. This should be with all of the plugs out and throttle wide open. To check your timing slide a long wooden dowel into cylinder #1 spark plug hole so it is resting on the piston. Slowly crank the engine over manually and watch the dowel travel. When the dowel reaches its highest point that is TDC. Check to make sure that the timing mark on the main pull lines up with the 0* mark on the timing cover. If it doesnt, the damper slipped. If it does then ensure the two cam marks are pointing straight up. If they are pointing straight down. turning the engine 360* will put them straight up. If they are not then your timing is off. Finally make sure that the alignment pin on the cam is in the middle of the three holes on each cam gear. If all these things check out, valve timing is not your issue.
If the teaspoon of oil test boosts your compression, then you probably need rings. My initial guess however is your MHG did not seal properly because you did not resurface the block.

You misunderstood. He said he poured oil on top of the pistons and it didn't leak by the rings. Simply pouring oil in a cylinder and seeing if it stays there does not tell you if the rings are bad or not. Nor does it help rings seal or reduce blowby while the engine is running.

A dry/wet compression test IS a good way to tell if you have ring problems however.

 

[lewis15498]

You misunderstood. He said he poured oil on top of the pistons and it didn't leak by the rings. Simply pouring oil in a cylinder and seeing if it stays there does not tell you if the rings are bad or not. Nor does it help rings seal or reduce blowby while the engine is running.

A dry/wet compression test IS a good way to tell if you have ring problems however.

Reading it again, yeah I may have missunderstood him. Either way now he knows. Sorry to call you out like that then.

 

[7mgte1988]

My timing is right on the mark but there is one thing i did not do as in resurface the block... I never thought cast iron would warp...
I put the mineral oil on the pistons when there was just a bare block in the car and it held it for weeks..
THX for the input....

 

[lewis15498]

My timing is right on the mark but there is one thing i did not do as in resurface the block... I never thought cast iron would warp...
I put the mineral oil on the pistons when there was just a bare block in the car and it held it for weeks..
THX for the input....

Its not so much warpage as an RA thats out of spec for your MHG.

 

[thorpedo]

Reading it again, yeah I may have missunderstood him. Either way now he knows. Sorry to call you out like that then.

No problem, understanding the op is no small task lol (no off)

Lewis is probably correct, your hg isn't sealing.

 

[7mgte1988]

Yea i have no choice but to tear her down again.. Wut is RA?? i didnt catch that..
Could it still be the gasket and block as of now i have the ARP studs at 90lbs with the copper on the gasket??

 

[bluepearl]

Leakdown test

 

[lewis15498]

Yea i have no choice but to tear her down again.. Wut is RA?? i didnt catch that..
Could it still be the gasket and block as of now i have the ARP studs at 90lbs with the copper on the gasket??

http://en.wikipedia.org/wiki/Roughness
RA is covered in section 4: Parameterization but I would reccomend taking a minute and reading the whole thing. Your MHG comes with a max Ra spec. I'm not an expert on the subject though, I reccomend doing your own research.

 

[7mgte1988]

U Have a good point but i seriously dont think HKS would sell something that would defect so easily..
So are u saying the headgasket can only be turqed to a certain limit??

 

[lewis15498]

U Have a good point but i seriously dont think HKS would sell something that would defect so easily..
So are u saying the headgasket can only be turqed to a certain limit??

I think you misunderstood. I doubt your HG is defective. What I was saying is your Headgasket has a max Ra spec. The Ra number is the variation in the surface measured in microns IIRC (I'm no machinist, so dont quote me) What this means is that the surface of the head and the block must both be lower than this number in order to ensure that it seals properly. Multi layer steel gaskets such as yours are more desireable because they are stronger than composite gaskets. The downside to this is it is also less willing to to conform to the surface irregularities on the head. Because of this MLS gaskets have a much lower max Ra than composite gaskets. This makes it neccesary to have both the block and the head machined. Your head should still be fine, but you do need to have the block done. The good news is your HG is reusable. You do however need to separate all the layers and clean all the viton material off of it and then coat them with copper spray. For the record, on a new MLS gasket you should not use the copper spray as its not needed as the viton is there. I think I remember being told the spray attacks the viton, but again dont quote me on that. Before you waste your time cleaning all the viton off your HG Have the machine work done, and have them measure the block and head height, then use these figures to calculate the proper HG thickness. (theres at least one thread out there dedicated to figuring this out) To thin of a HG will increase your compression ratio and also offset your valve timing, two things you don't want to do.

Contact HKS tech, they will be happy to tell you what the Ra needs to be.
(310) 491 3300
M thru F 8am-5pm PST

 

[hvyman]

so this is a hks mhg on a block that has not been resurfaced? hks mhg's need the smoothest surfaced on both the block and head than any other mhg.

 

[CajunKenny]

Something else I noticed in the op's info is that he stated he has an HKS MHG and he sprayed it with copper spray.

This is a big no no...

Hopefully I mis-understood; but, if not. Read this!

http://www.supramania.com/forums/sh...Spray-Sealer-on-a-MHG-Might-Want-to-Read-This

 

[7mgte1988]

This is a big help well guys just to let u know dont use the copper on the HKS Metal Gasket it will not seal......That was the only thing i did differant this time and lose my compression..
I cant belive i F my Car up lol

 

[lewis15498]

This is a big help well guys just to let u know dont use the copper on the HKS Metal Gasket it will not seal......That was the only thing i did differant this time and lose my compression..
I cant belive i F my Car up lol

I'm saying this because I dont wan't you to make the same mistake twice. The copper spray is not the primary issue here, Not resurfacing the block is.

 

[4U2QUIK]

90lbs? wtf? go back and read the instructions that came with the studs.

 

[paradox616]

it depends if he used moly graphite lube or engine oil/anything at all. Torque applied to the bolt/stud when tightening does not nesssecarily = clamping power, this is what the instructions that come with the arps say, for example arp specify for one headstud product
30w oil | arp lube
95 ft lbs 75 ft lbs

i torqued mine to 78ft/lb with arp lube, which is more than hes torqued his to if he used engine oil.

Unforntuately too many people learn the woes of metal headgaskets the hardway, including myself. First time round i decided to cut a corner and i paid deerly for it. From what i hear, looks like you've got some scrubbing to do!