Thread: My Compression test results are all over the shop

Heads have gone back on now. Should be finished tomorrow.

Originally Posted by LOVEMYRANGIE

Take the heads into a shop and get them skimmed. As this wasnt done last time, aluminium heads have a habit of warping when removed, and unless refaced, will leak when used with laminated steel gaskets. Not tensioning in the correct sequence will also contribute to this. You could use composite type gaskets, but in a high CR and gas engine, dont waste your time.

The heads were skimmed when I overhauled the engine so I have not had this re-done. Bolts were retensioned in the correct order.

Originally Posted by LOVEMYRANGIE

Also, when tensioning, the 4 headbolts outside the rocker cover are the LAST ones to be done and only require something like 20ft/lb torque. Some people even leave these out as they have been attributed to bad sealing from unequal forces over the headface.

Yup, this was done 70ftlb on the main bolts around each cylinder and 40ftlb on the outermost bolts.

Originally Posted by LOVEMYRANGIE

As for the glazing, you gonna need to re hone it, that means you're going to need to pull it out.

While this is really what should be done, i don't have time to do it. I have to have the car back on the road by saturday for a 4wd trip i'm running. So it has gone back together without this being done. I know it should have been done, but the main problem was the gasket. If I had more time I would have done the bores and rings.

Originally Posted by LOVEMYRANGIE

One last thing, about your fathers idea of lower compression from valve lapping increasing the displacement, dont listen to your father and keep him away from beer and engines! FFS......

Ah well, sometimes you get that.

Shortcuts WILL come back to bite you

When your going to sort the preignition?

Although you didn;t deck the heads again, you did flat face them and check for true??

You need to stop the death rap or it will be a hole on a piston or leg out of bed if the head gasket doesn't pop again. Just lock it and run static till just before ping then shorten curve to suit then play with springs. Cheap and easy even if not perfect will be better than killing it

Originally Posted by Rangier Rover

Just lock it and run static till just before ping

be better than killing it

Yep .. set it at 18 .. 25 degrees???

Can you get "lazer cut" thicker head gaskets to reduce the compression???
(Local engineering joint / not off the shelf product) ... Would that work??

Originally Posted by mike 90 RR

Yep .. set it at 18 .. 25 degrees???

Can you get "lazer cut" thicker head gaskets to reduce the compression???
(Local engineering joint / not off the shelf product) ... Would that work??

The CR will be fine with gas, its just when its that high its imperative not to let it rattle as the slightest ping ain't good as opposed to a bit of rattle at 8.5:1 won't hurt much

G`day Stirling

You have some interestimg carbon patterns , a bit more colour in the valley than i`d expect from an lpg runner also the different shades and different amounts of moisture that makes up the carbon is also interesting .

Putting it back together to use it makes sense and gives you time for a plan of action .

I`m only guessing but i wouldn`t be surprised if it has chrome top rings and probably the glazzing cause , which inturn is giving more colour through out and adding to the piston tops but pics don`t always tell the full tale .

The piston tops are not of the type i expected for 10s but may well be depending pin placement but the concave doesn`t look right to me but i can`t judge a depth from the pics either .

I think what is needed is to work out why it`s producing so much carbon , running lpg it shouldn`t be making as much as it is .

The gaskets should seal ok but i hope you tidied up some of the threads in the block and any highs from alloy movement , Heads i`d think if only ever skimmed should be ok .
If you have a need i can give you the helicoil details for the block to headbolts threads , sometimes there is a need to go over spec on the bolts but to get there the thread in the alloy can let go , so the need foe helicoil .
Fine in a 3.5 asking for trouble in a bigger holed one just good ordinary type head bolts seem ok there .

Cheers
Peter

Originally Posted by PLR

G`day Stirling

You have some interestimg carbon patterns , a bit more colour in the valley than i`d expect from an lpg runner also the different shades and different amounts of moisture that makes up the carbon is also interesting .

Putting it back together to use it makes sense and gives you time for a plan of action .

I`m only guessing but i wouldn`t be surprised if it has chrome top rings and probably the glazzing cause , which inturn is giving more colour through out and adding to the piston tops but pics don`t always tell the full tale .

The piston tops are not of the type i expected for 10s but may well be depending pin placement but the concave doesn`t look right to me but i can`t judge a depth from the pics either .

I think what is needed is to work out why it`s producing so much carbon , running lpg it shouldn`t be making as much as it is .

The gaskets should seal ok but i hope you tidied up some of the threads in the block and any highs from alloy movement , Heads i`d think if only ever skimmed should be ok .
If you have a need i can give you the helicoil details for the block to headbolts threads , sometimes there is a need to go over spec on the bolts but to get there the thread in the alloy can let go , so the need foe helicoil .
Fine in a 3.5 asking for trouble in a bigger holed one just good ordinary type head bolts seem ok there .

Cheers
Peter

I think the carbon may be the valve seals letting a bit down at times and posible rich as gas can do at some point. The rest may be from detonation