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92mm pistons ??

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ceejay manishka mitchel
sri lanka, UK   GBR
1972 MG MGB
Hi all,

What does it take to install 92mm pistons in a TR4 block ?

Does the block itself need to be modified ?

Can a standard or replacement steel crank be used or does it need a special offset crank ?

What cubic capacity does that bring it upto with the standard stroke ?

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t.lay Avatar
t.lay Tom Lay
Grayslake, IL, USA   USA
If my math is right, a 92mm set would be 2446 displacement. Personally, going above the 89mm sets would have me looking more at engine swaps - just way more effort than I think you would get for a return trying to up the displacement much more than 2188. You would have to either live with very thin liner walls. Modifying the block - not sure - if you can open it up much without going straight into the water passages.

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ceejay manishka mitchel
sri lanka, UK   GBR
1972 MG MGB
Thanks for your input.

I'm building a TR4 engine for someone who is keen on getting the maximum power out of the TR4 block.

The car will be used only for week end driving on the road and that too in the city mainly and not on motorways or highways.

The power will be used for rapid acceleration and overtaking. That too not all the time, just now and then for kicks.

I'm still keen to find out if the 92mm pistons can be used with thin liners and not needing to modify the block.

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yellowbookroad Avatar
yellowbookroad Gareth T
Somewhere in, Estonia   EST
1970 Triumph 2.5 PI MkII "Permanently NICKED Nickname"
You can do exactly the same as on the Jaguar, so please "shut up" and don't tell everyone in the world this thing!!
I won't tell you exactly how to do it, but here are the hints.

The Jaguar XJS engine has exactly the same bore & stroke, as well as the same big end sizes.
Bore 91mm stroke 92mm

Take 4 out of a set of rods from the XJS and throw away your old Triumph ones.
The Jag ones are good quality steel with superb quality rod bolts and are usually to within 1g of balance.
You can actually take off 100g from them if you want them lighter (!)

Get a piston of 91mm and the correct pin height to match the new length of the rod.
(You might just find the jaguar 2.9L piston is what you need...or the V12 one which has a bore of 90mm....)

(There are also several good modern Karl Schmidt or Mahle pistons which fit with little modification)
Get some 91mm liners (look through the liner books and you will see what needs to be modified to fit.......)

Have fun.
This is a very cheap way of getting what you are looking for..or you can bring it to me and I'll do it. I've got loads of spare rods winking smiley

You don't need to go as big as 92mm.
The biggest performance improvement is to be had by getting the head flowed properly, and believe me it's none too easy..

Cheers



Edited 4 time(s). Last edit at 2011-10-07 04:30 PM by yellowbookroad.

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JimG Avatar
JimG Jim G
Aurora, CO, USA   USA
I would forget the 92's. The 89's are very thin as it is and after the relief
in the tops of the liners is cut for the intake valve ( if the head has been milled )
you don't have much liner left to seal the head. Even for an 89mm motor you have to mod the head a little bit. I don't know how you would keep a head gasket in it with 92mm.
As far as I know it has only been done in the U.K.

jim g

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TR3barton Avatar
TR3barton John Taylor
Greenfield, MA, USA   USA
Hello,

Moss sells 89mm pistons and liners.

I bought a set from British Frame and Engine likely the same that Moss sells . They came with Wesco forged pistons and are great looking and fit was perfect. I am told the liners are made by LA Sleeve. They are in a block and the motor should be finished in a few days.

Be Careful of head gaskets !!!!!!!!

There are lots of options and I have chosen the steel unit, $$$ ouch. Stay tuned. Moss may try to sell their standard head gasket and it will NOT work (IMHO).

Check out Rasetorations(sp) in the UK.

Best
John
jat1127@hotmail.com

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JGug1 Avatar
JGug1 Silver Member James Guglielmino
Mission, KS, USA   USA
This is an ANCIENT thread but I must tell you that I am soon to find out how strong the 92 mm cylinder engine is because that is what is in my engine. The engine is still on the bench but it is nearly done. The head has been reworked and surfaced. If it blows up, I'll let you all know. Forgive my reviving a 7 + year old thread.

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  Perdido thanked JGug1 for this post
Geo Hahn Avatar
Mt Lemmon, AZ, USA   USA
No forgiveness necessary - I await the result with interest.

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JGug1 Avatar
JGug1 Silver Member James Guglielmino
Mission, KS, USA   USA
I had come to understand that the metal in the 89 mm cylinders was advanced over the older cylinders but frankly, I cannot imagine 3 mm bigger.......I am very found of my restoration shop. Both partners are friends and I trust them both.

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JGug1 Avatar
JGug1 Silver Member James Guglielmino
Mission, KS, USA   USA
Update: Because of my interest in these various options, I kept looking for 92 mm cylinders. The discussions I found indicated that the block had to be machined to accommodate them. So I texted my restorer. He told me he had misspoken and that my cylinders are 89 mm. I find them by Googling. The metal on them is 2 mm thicker and they are press in without machining the block. I kind of think 89 mm will be big enough. I believe it is about 2.3 liters +-

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Tommys4 Platinum Member Thomas G
Ojai, Calif., USA   USA
Ken Gillanders had 92mm pistons in his TR2

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Motorsport Micky Avatar
Motorsport Micky Silver Member Michael Richards
Sutton in Ashfield, Nottinghamshire, UK   GBR
Most of the power increase in the 92mm bore size comes from the increase in breathing from the moving of the bores away from the inlet valve.
Why bother ?

The 92 mm bore makes sealing the head a problem, the clamping space is reduced all around the liner and the block needs work because the liners have to be accommodated. Half of a 92mm dia is 46mm and half of a 89 mm bore is only 44.5 mm, so on a 89mm bore if you offset the cylinder head by 3mm that makes the position of the liner wall adopt, at it's maximum point, even further away than the same position as a 92 mm engine, ie 89 divide in half = 44.5 mm plus a 3mm offset = 47.5mm, 1.5mm more than the 92mm dimension of 46mm..
I agree there is a small corruption on the flow with the diverging arcs of the 92mm against the 89mm liner but because this is only on a 20% of the bore (the "bath tub" combustion chamber carrying the valves is offset towards the passenger side) I measure it as less than 6%.

"Don't let the perfect be an enemy of the good"

The 89mm bore with a 3mm offset head when carefully built gives excellent power results and is reliable, not only that but being able to be engineered with machinery commonly held in most home garages.The first offset head I did in the car I raced in winter 1988 is still racing, (picture below) winning and reliable.
There is an increase in the order of magnitude to seal and run a 92mm engine to be reliable, I considered when first offsetting the head why stop at 3mm ? almost for the same reasons. Every further 1 mm more offset reduces clamping available liner space for the head where it is most problematical, around the valve "bathtub" area where the sealing rings run closest.
Many of the TR competition cars now running use offset heads as to what bore size they use comes down to depth of pockets and available technical help.



Edited 3 time(s). Last edit at 2019-03-10 12:36 PM by Motorsport Micky.


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TR4 Race car (500x374) (150x112).jpg    4.8 KB
TR4 Race car (500x374) (150x112).jpg

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JGug1 Avatar
JGug1 Silver Member James Guglielmino
Mission, KS, USA   USA
A very informative and useful post, Motorsport Mickey. It is important to remember, however, that most of us are driving cars that we want to be able to tour with, as well as chase around on curvy roads. My sense is that once we get into going considerably further with our engines, we are treading on engines that will require meticulous tending, often by specialists. In the end, I am rather glad that my restoration shop is going with 89 mm cylinders. These are apparently as big as you can go without reworking the block. For me, that is a bit of a bridge too far.

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Motorsport Micky Avatar
Motorsport Micky Silver Member Michael Richards
Sutton in Ashfield, Nottinghamshire, UK   GBR
I think that's what I said James,

to go 92mm would take block modification, whereas the 89 mm is slip the replacement liner in and is no more difficult than a standard liner fit. The offset head takes about 2.5 hours of machining time (less time than you'll spend having it gas flowed) and I did it at home, any good machine shop will do it even easier.
I sort of got the wrong impression and thought you wished to go for a power engine which the offset will give, and as I mentioned the same engine is in the car and running since 1989 season, admittedly it's had various other components refreshed since then but the offset head is still on and working...not too bad for a 30 year old modification which I guess could be classified as reliable. Nothing in that modification would stop a car being used for street and touring work, even though your head is already reworked your restoration shop could carry out the mod without any interfering with your work carried out previously.

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JGug1 Avatar
JGug1 Silver Member James Guglielmino
Mission, KS, USA   USA
Thank you, again. I was under the impression that the mod to use 92mm cylinders was likely to not be reliable. Your reminder that yours is 30 years old and still going denies that.
As my engine is almost completely assembled with 89 mm cylinders, I won't go down the road you did (you may remember that my restoration guy misspoke when he initially said that my cylinders were 92mm).....Still, I admire what you have done.

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