MA12 Head, Maximum that can be skimmed?

M

Mulbers

Guest
Yo,

Does anyone know on here know what the max that can be skimmed off an ma12 head?

Mines been done after a blown head gasket, but it has been skimmed before hand too, so its a little on the thin side now.

If it blows again it will be closer to an ma10 than an ma12.

Regards
 
not sure how much can be skimmed chap but the 12 part of the ma12 refers to the capacity so skimming it wont reduce the capacity it only effects the compression ratio :)
 
Speedle said:
not sure how much can be skimmed chap but the 12 part of the ma12 refers to the capacity so skimming it wont reduce the capacity it only effects the compression ratio :)
Click to expand...

Speedle, I know what the numbers refer to, but thank you anyway.

If the head has been skimmed and the compression is higher then there must be a reason for this. i.e., the bore stroke has been altered and your putting the same amount of air and fuel into a smaller space. wether or not they take the volume of the head into consideration when they state 998cc or whatever it may be I don't know, either way the engine capacity has been changed even if by a small amount.

Mine has had 62thou taken off so was a bit worried about the valve going clunk on the top of my pistons.

Anyway, it was just an off the cuff comment.:grinning:

Cheers
 
tbh mate skimming that little will hardly make any difference at all im sure it will be fine to skim it again, best thing to do would be to as bobsp16 as he's no doubt had many done and would know what the max you can skim off is
 
62thou off it christ!! dont over rev it,My race engine's got 50 thou off it and when it jumped out of gear early this year when i was racing and this is what happend....AND I HAVE 4 LIKE THIS....
23-Picture%20406.jpg
 
bobsp16 said:
62thou off it christ!! dont over rev it,My race engine's got 50 thou off it and when it jumped out of gear early this year when i was racing and this is what happend....AND I HAVE 4 LIKE THIS....
Click to expand...

O horse ####.

What would you say is over reving it? I go to 6k on a regular basis. Well iv been running it on 50thou for a far few miles and has been ok. Compression will be through the roof, or bonnet if it goes wrong. ha ha.

im puttin it back together tonight and will be turning it by hand before i start it. il post up pictures later.

Regards
 
im affraid now mines been skimmed twice! dunno how much has been taken off though. how much is a rev limiter? and how easy is fitting? id imagine its fairly simple.
 
Ian said:
or just dont rev it as much ;)
Click to expand...


I agree, you should have a bit of control your foot isn't made entirely of iron :p

The only time I'd agree with using a rev limiter like that is in Bobs situation where racing.

Other than that, why would you want to rev to nearly 7k on a road anyway?
 
yes and ive hard some of you boy racer seeing how long they can stay in each gear,max power is at 5600rpm but they will rev on another 1000 in standard form.
if youve had your head skimmed for standard reconditioning thay will have only taken about 5 thou off just to get it true and flat again.
 
bobsp16 said:
yes and ive hard some of you boy racer seeing how long they can stay in each gear,max power is at 5600rpm but they will rev on another 1000 in standard form.
if youve had your head skimmed for standard reconditioning thay will have only taken about 5 thou off just to get it true and flat again.
Click to expand...

Total agree with you dude!
 
Mulbers said:
Speedle, I know what the numbers refer to, but thank you anyway.

If the head has been skimmed and the compression is higher then there must be a reason for this. i.e., the bore stroke has been altered and your putting the same amount of air and fuel into a smaller space. wether or not they take the volume of the head into consideration when they state 998cc or whatever it may be I don't know, either way the engine capacity has been changed even if by a small amount.

Mine has had 62thou taken off so was a bit worried about the valve going clunk on the top of my pistons.

Anyway, it was just an off the cuff comment.:grinning:

Cheers
Click to expand...

Skimming the head will not alter the capacity of the engine.

You still have the same bore & stroke, just a slightly smaller combustion chamber, hence the higher compression.
 
Mulbers said:
Speedle, I know what the numbers refer to, but thank you anyway.

If the head has been skimmed and the compression is higher then there must be a reason for this. i.e., the bore stroke has been altered and your putting the same amount of air and fuel into a smaller space. wether or not they take the volume of the head into consideration when they state 998cc or whatever it may be I don't know, either way the engine capacity has been changed even if by a small amount.

Mine has had 62thou taken off so was a bit worried about the valve going clunk on the top of my pistons.

Anyway, it was just an off the cuff comment.:grinning:

Cheers
Click to expand...

Do you actually know how you work out compresson ratio?

What makes you think that skimming the head reduces the bore (diameter) or stroke (crank), therefor engine capacity.?

All you do by skimming the head is alter the compression ratio, and also as a side effect the cam timing of the engine. The capacity of the engine remains the same. the piston stoke remains the same the bore remains the same the only difference is the compression ratio, which by the way if raised your more likely to keep blowing headgaskets.

Finally there is no need to be so rude, as from your post above you dont know what the numbers refer to. It would pay to listen to some of the advice from people on here rather than assume you know it all.
 
i thought i was right about it not changing the cappacity thought i was going mad for a second there ;) i mean i have been playing with k10 for years now so i hoped some of the stuff i knew was right, at one point i have the 2nd most modded k10 next to dans.... short lived fame! lol!

thanks Ed ;)
 
Ed said:
Do you actually know how you work out compresson ratio?

What makes you think that skimming the head reduces the bore (diameter) or stroke (crank), therefor engine capacity.?

All you do by skimming the head is alter the compression ratio, and also as a side effect the cam timing of the engine. The capacity of the engine remains the same. the piston stoke remains the same the bore remains the same the only difference is the compression ratio, which by the way if raised your more likely to keep blowing headgaskets.

Finally there is no need to be so rude, as from your post above you dont know what the numbers refer to. It would pay to listen to some of the advice from people on here rather than assume you know it all.
Click to expand...

i would assume your a edited, and id be right, but #### it.
 
Unfair Dismissal?

Dudes!

I thought this thread was pretty interesting...its a shame it came to this.

As a totally independent (non-biased) party, I felt that; although Mulbers started off an interesting thread...it seemed that He/She was hammered a bit too hard on His/Her misunderstanding of what people were saying.

This thing on capacity being specified as bore x stroke is not the same as physical capacity...and it is understandable that not everyone knows or can grasp this.

I feel that Mulbers was provoked into cursing and should be given a chance.

I realise that MSC’s decision is final BUT:
At the risk of getting kicked or warned myself, I think it would be nice Admin & Moderators were a little more compassionate with members who don't quite get the technical bits right first time. (I am admin of forums elsewhere so I do appreciate both sides of this)

A public "Bye Bye" was certainly not necessary IMO.

Kicked while down…/….I have the power

Sorry if I’ve got this totally wrong
 
I agree


SammoHung said:
Dudes!

I thought this thread was pretty interesting...its a shame it came to this.

As a totally independent (non-biased) party, I felt that; although Mulbers started off an interesting thread...it seemed that He/She was hammered a bit too hard on His/Her misunderstanding of what people were saying.

This thing on capacity being specified as bore x stroke is not the same as physical capacity...and it is understandable that not everyone knows or can grasp this.

I feel that Mulbers was provoked into cursing and should be given a chance.

I realise that MSC’s decision is final BUT:
At the risk of getting kicked or warned myself, I think it would be nice Admin & Moderators were a little more compassionate with members who don't quite get the technical bits right first time. (I am admin of forums elsewhere so I do appreciate both sides of this)

A public "Bye Bye" was certainly not necessary IMO.

Kicked while down…/….I have the power

Sorry if I’ve got this totally wrong
Click to expand...
 
i was also following this thread an it was good and you are right to an extent he was slammed slightly but that was a rediculous comment made towards ed. (i saw it before the admin to :p). He was being educated about his car thats all!
 
Because there are some who simply do not fit into the way in which the club is run.
His banning is not a kneejerk reaction. Its a result of many previous warnings, both recorded and spoken. Also contempt for other admin on this site (particulary againt Arnold) we simply do not tolerate it. If I look through the MSC admin logs there are numerous problems and complaints of attidude etc. Also are notes of second chances, and a reduction in previous warnings, so he cannot have any excuse what so ever for this kind of behaviour.

These posts will stay for a short time then im going to clear this thread up.

Just to add the formula for compression ratio is:

(Swept Volume + Clearance Volume) / Clearance Volume

Swept volume is the amount of air the piston moves, and the clearance volume is the area above the piston @ top dead centre.
 
sorry in advance but im bored and ill and was in a educational mood and thought id educate myself and share in case any one else wants to do the same; COMPRESSION RATIO FORMULA




1. Determine the displacement of your engine. Displacement formula is:

BORE X BORE X STROKE X .0031416 = DISPLACEMENT

Example: 92 x 92 x 82 x .0031416 = 2180cc

2. Determine the swept volume of one cylinder:

Example: 2180cc divided by 4 = 545cc

3. Determine the deck volume of each cylinder. The deck volume is the distance from the top center of the piston to the top of the cylinder when the piston is at top dead center. Measurement is made in thousandths.

Example: on cylinder #1 you measure and find you have .020" deck height.

BORE X BORE X DECK HEIGHT X .01996 = CC"s

Example: 92 x 92 x .020" x .01996 = 3.378cc's

Measure each cylinder.

4. Measure the volume in each cylinder head. To do this, use a piece of plexiglass cut to fit in the cylinder head to cylinder mating area. Drill a 1/4" hole in the center of the plexiglass. Lightly grease the edge of the plexiglass and install in the head. (Spark plug and valves have to be installed) with a syringe graduated in cc's fill the cylinder head chamber up with a light weight oil. Record the measurements. Repeat for other three chambers. Average cc volume of a new head chamber is between 47 and 51 cc's.

5. You now have all the measurements to determine your compression ratio.

one cylinder swept volume + deck cc + head cc

deck cc + head cc

Example: 545 + 3.378 + 48 = 596.378

3.378 + 48 = 51.378 = 11.6:1

In this example, 11.6:1 is the actual unadjusted compression ratio for one cylinder. Add cylinder shim thickness which will increase the deck cc volume and refigure compression ratio. This must be done for all cylinders. Average deck height shim for use on a 2180cc engine will be between .150" and .185". We use a .177" shim for AVGAS and a .216" or .256" shim for unleaded premium auto fuel. Lower is better for increased engine life and fewer valve related problems.
 
TBH i think Ed is right on this one although i dont always agree with his methods, its a bit annoying when new people signup and start telling people who have been here years they are wrong, i mean i dont even own a micra anymore but im one of the very few on here that stick around and try to help out the k10 owners with what i feel is a huge knowledge of the k10. to be told your wrong by people who have been on here 5 mins compared to me is a bit annoying to say the least.

anyway from what i see this matter is closed so i will leave it there
 
Apology to Ed & MSC

Bombz: a thoroughly wikid post Nice one..

ED: Sorry for putting MSC decisions under the spot lamp (not one of my best moves so far, and it was out of order for me to do so). I hope you will accept my apollogy if this has caused you and / or MSC any grief..

Next time I will keep my neb out & trap shut

sincerely,

Richard
 

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