How much is it safe to shave off a block?
08-06-2012, 02:07 PM
#16
Rennlist Member
I have thought about welding, but considering I have been unable to find someone willing to weld my exhaust I don't think I can find someone with the expertise to do the job.
My cylinder head measures 23.89mm. after refinishing. The manual states 24 +- 0.1mm with standard 1.1 gasket and 1.4mm gasket from 23.8 and less on the cyl. head. The proper thing to do would be to shave the block, have it measured and then buy the gasket, but I don't think I will have time for that if I'm not going to loose out on the last bits of this season as well. I'm thinking I should be OK with a 1.4 MLS gasket.
Where is the best place to buy the MLS gaskets and how quickly can I get my hands on one? I have one more week of shop time before real life catches up on me again.
Where do you measure the block height? I need to measure it before and after machining.
Thanks to all for helping me out through this endless series of setbacks
My cylinder head measures 23.89mm. after refinishing. The manual states 24 +- 0.1mm with standard 1.1 gasket and 1.4mm gasket from 23.8 and less on the cyl. head. The proper thing to do would be to shave the block, have it measured and then buy the gasket, but I don't think I will have time for that if I'm not going to loose out on the last bits of this season as well. I'm thinking I should be OK with a 1.4 MLS gasket.
Where is the best place to buy the MLS gaskets and how quickly can I get my hands on one? I have one more week of shop time before real life catches up on me again.
Where do you measure the block height? I need to measure it before and after machining.
Thanks to all for helping me out through this endless series of setbacks
If you want to measure and order an MLS, then I would measure from the deck to the piston at TDC (dial gauge fixture is best, but straight edge and feel gauge can work it the pistons remain below the deck). Measure along the wrist pin axis as the height will vary elsewhere as the piston rock on the pins. If everthing is stock, you can honestly probably do fine eyeballing it -- just make sure the pistons come up flush with deck (+/- the thickness of a page or two of paper) then order a standard thickness gasket.
08-06-2012, 05:42 PM
#17
Burning Brakes
Thread Starter
Thanks for your detailed explanation. I have taken some macro pictures of the scratch to determine how bad it is. It looks to be roughly 1 tenth of a millimetre.
I don't mind going to a thicker gasket, but I will go with a standard gasket unless someone says I can safely drive 320 miles with a leaking MLS (I doubt it). My machinist is on holiday at the moment, so machining the block will have to wait a little while.
Do you think I can get by with the standard gasket even if I shave the block as long as the pistons are below the deck after shaving? I have a dial gauge with fixture so I can do it properly.
Where do you measure the actual height of the block, on each end?
I want to measure it before it is shaven so I know how much was taken off but I don't have calipers that big.are there any other reference planes on the block I can use?
What is worse for performance? Retarding the cam or lowering the compression with a thicker gasket?
I don't mind going to a thicker gasket, but I will go with a standard gasket unless someone says I can safely drive 320 miles with a leaking MLS (I doubt it). My machinist is on holiday at the moment, so machining the block will have to wait a little while.
Do you think I can get by with the standard gasket even if I shave the block as long as the pistons are below the deck after shaving? I have a dial gauge with fixture so I can do it properly.
Where do you measure the actual height of the block, on each end?
I want to measure it before it is shaven so I know how much was taken off but I don't have calipers that big.are there any other reference planes on the block I can use?
What is worse for performance? Retarding the cam or lowering the compression with a thicker gasket?
08-06-2012, 09:13 PM
#18
Rennlist Member
As for driving on a leaking HG, it all depends how bad the leak is. I've had gaskets that don't leak at all unless you get on the boost, and others that literally flooded the oil pan with coolant within a mile or two.
If the pistons are at or below the cylinder tops, you can use a standard gasket. The pistons in my current motor stand about 4 thousandths above the deck, and a standard gasket is still working fine.
There may be reference marks on the block, but I've never used them or noticed them in the tech spec book. If you measure piston depth before and after you can tell how much they removed (assuming it was flat to start with -- otherwise, the amount they remove might vary across the deck).
Re retarding cam v thicker gasket, not sure what you are after with that quesiton. You'd be doing those things to overcome the new machining dimensions, so you'd be just getting the motor back to stock. That said, all other things equal, lower compression will reduce performance whereas retading the cam shifts the power curve.
If the pistons are at or below the cylinder tops, you can use a standard gasket. The pistons in my current motor stand about 4 thousandths above the deck, and a standard gasket is still working fine.
There may be reference marks on the block, but I've never used them or noticed them in the tech spec book. If you measure piston depth before and after you can tell how much they removed (assuming it was flat to start with -- otherwise, the amount they remove might vary across the deck).
Re retarding cam v thicker gasket, not sure what you are after with that quesiton. You'd be doing those things to overcome the new machining dimensions, so you'd be just getting the motor back to stock. That said, all other things equal, lower compression will reduce performance whereas retading the cam shifts the power curve.
08-07-2012, 04:36 AM
#19
Burning Brakes
Thread Starter
Thanks Tom.
I don't think I would dare set out on such a long journey on a leaking head gasket anyway so I might as well get a stock gasket as they are available over here. If the block is machined flat enough for the MLS there should be no need to have the block machined again if I want to try one if/when the stock one goes.
I was hoping to avoid installing bearings, crank and pistons before handing in the bare block. I don't like having to torque the main studs more times than absolutely necessary.
Re. retarding cam vs. thicker gasket and loss of compression:
I don't have an adjustable cam gear so:
If I shave the block and use the stock gasket I will get cam retardation but higher compression relative to the option below.
If I shave the block and use a thicker gasket I will get cam advance and lower compression relative to the above.
Which of these is likely ot be the best option for performance?
I don't think I would dare set out on such a long journey on a leaking head gasket anyway so I might as well get a stock gasket as they are available over here. If the block is machined flat enough for the MLS there should be no need to have the block machined again if I want to try one if/when the stock one goes.
I was hoping to avoid installing bearings, crank and pistons before handing in the bare block. I don't like having to torque the main studs more times than absolutely necessary.
Re. retarding cam vs. thicker gasket and loss of compression:
I don't have an adjustable cam gear so:
If I shave the block and use the stock gasket I will get cam retardation but higher compression relative to the option below.
If I shave the block and use a thicker gasket I will get cam advance and lower compression relative to the above.
Which of these is likely ot be the best option for performance?
08-07-2012, 11:48 AM
#20
Rennlist Member
Based on your head measurements, the factory manual says to use the stock gasket, right? Or am I misunderstanding your post? Not sure why you are pondering thicker gaskets?
I assume there is a way to measure the deck without pistons, but I've never done it because the thing you really need to know is how much room the pistons have. If you measure without the pistons -- how will you know how much they can cut off the top? At .004" off the deck, the effect on performance will not be measurable really, whether from cam timing or compression, so I personally would not let that factor into the equation. If it were me, I'd just have it skimmed and tell the shop not to remove more than .005" unless they call first.
I assume there is a way to measure the deck without pistons, but I've never done it because the thing you really need to know is how much room the pistons have. If you measure without the pistons -- how will you know how much they can cut off the top? At .004" off the deck, the effect on performance will not be measurable really, whether from cam timing or compression, so I personally would not let that factor into the equation. If it were me, I'd just have it skimmed and tell the shop not to remove more than .005" unless they call first.
08-07-2012, 01:46 PM
#21
Burning Brakes
Thread Starter
The manual says to use the stock gasket down to 23.80mm I'm at 23.89mm so I was still planning to use the stock gasket. However, if I remove another 0.1mm off the block the effect would be the same as removing 0.1 off the head, right? I will be in the territory where the manual says to use the thicker gasket (23.9mm - 23.6mm). Am I on the right track or did I miss something along the way?
