The V8 Owners Forum -

As the subject line really- my Dad had a tin gasket go on his 3.5.

Now fitting 10 bolt heads with composites, but his new gaskets have no word "top" on them to identify which way up they go.

Any pointers?

Thanks!

Look at the gaskets and you may find that the fire ring around each bore hole is slightly wider on one side. Fit this side onto the block.

Thanks Perry, will let you know how it goes

" Look at the gaskets and you may find that the fire ring around each bore hole is slightly wider on one side. Fit this side onto the block "

I don't have the answer or am saying Perry is wrong but why?

My logic would say that if there is a difference in fire ring width, then I would fit the wide side upwards - less contact pressure on the aluminium head face so less chance of face sinkage. The block face of course has an iron liner to carry the higher contact pressure from the thinner/smaller area fire ring.

Discuss ? ?

Russ

russell_ram wrote:" Look at the gaskets and you may find that the fire ring around each bore hole is slightly wider on one side. Fit this side onto the block "

I don't have the answer or am saying Perry is wrong but why?

My logic would say that if there is a difference in fire ring width, then I would fit the wide side upwards - less contact pressure on the aluminium head face so less chance of face sinkage. The block face of course has an iron liner to carry the higher contact pressure from the thinner/smaller area fire ring.

Discuss ? ?

Russ

Hi Russ,

I saw Perry's post and thought the same thing as you.

Maybe because a chamfer has been machined into the liner at the top the thinner fire ring would end up floating about in mid air if the thinner side was facing this chamfer?

Pete

sidecar wrote:

russell_ram wrote:" Look at the gaskets and you may find that the fire ring around each bore hole is slightly wider on one side. Fit this side onto the block "

I don't have the answer or am saying Perry is wrong but why?

My logic would say that if there is a difference in fire ring width, then I would fit the wide side upwards - less contact pressure on the aluminium head face so less chance of face sinkage. The block face of course has an iron liner to carry the higher contact pressure from the thinner/smaller area fire ring.

Discuss ? ?

Russ

Hi Russ,

I saw Perry's post and thought the same thing as you.

Maybe because a chamfer has been machined into the liner at the top the thinner fire ring would end up floating about in mid air if the thinner side was facing this chamfer?

Pete

Hi!!
I'm not sure I follow on the difference in contact pressure between the top and bottom of the gasket? The contact pressure surely is the same on each side of the gasket regardless of the amount of fire ring material ??

The liner top is flush with the deck. Or it should be. So fitting the wider side down gives you more steel to compress around the liner top and the deck face which is where the most likely point of leakage will be under heavy load. If the deck faces and heads are spot on then it shouldnt make a difference. But I always opt for more metal on the deck side. If the engine is not a race item then either way should be fine. Especially if you use VHT copper spray when fitting. Not a lot will get past that combo

Thats my view on this anyway

mgbv8 wrote:

sidecar wrote:

russell_ram wrote:" Look at the gaskets and you may find that the fire ring around each bore hole is slightly wider on one side. Fit this side onto the block "

I don't have the answer or am saying Perry is wrong but why?

My logic would say that if there is a difference in fire ring width, then I would fit the wide side upwards - less contact pressure on the aluminium head face so less chance of face sinkage. The block face of course has an iron liner to carry the higher contact pressure from the thinner/smaller area fire ring.

Discuss ? ?

Russ

Hi Russ,

I saw Perry's post and thought the same thing as you.

Maybe because a chamfer has been machined into the liner at the top the thinner fire ring would end up floating about in mid air if the thinner side was facing this chamfer?

Pete

Hi!!
I'm not sure I follow on the difference in contact pressure between the top and bottom of the gasket? The contact pressure surely is the same on each side of the gasket regardless of the amount of fire ring material ??

The liner top is flush with the deck. Or it should be. So fitting the wider side down gives you more steel to compress around the liner top and the deck face which is where the most likely point of leakage will be under heavy load. If the deck faces and heads are spot on then it shouldnt make a difference. But I always opt for more metal on the deck side. If the engine is not a race item then either way should be fine. Especially if you use VHT copper spray when fitting. Not a lot will get past that combo

Thats my view on this anyway

The top of the liner is not flush with the deck all the way round the bore, it has a chamfer to aid getting the piston rings into the bore. This chamfer will reduce the liner to fire ring contact area.

"The top of the liner is not flush with the deck all the way round the bore, it has a chamfer to aid getting the piston rings into the bore. This chamfer will reduce the liner to fire ring contact area."

???

So the liner is flush with the deck apart from the bit that isnt there ??

So its still flush with the deck then.... And therefore the top edge of the liner still forms part of the total contact area on the gasket as it is level with the ally of the deck face. This was my own reasoning behind having more fire ring metal on the deck side. It gives you more surface contact area outside the fire ring. Fitting the gasket the other way up will still see the same amount of fire ring metal exposed at the top of the liner. ??