OHC 8V 1300 to 1400 Engine conversion - Looking for info

[Royston]

Just wondered if anyone has any magazine features or information on the above

I am considering upping the Sport engine using the age old 1.2 pistons (I have some new ones in stock)

Engine is now stripped and looking to prepare it fr the machine shop, needs reboring anyway

Main concern is the increases compression ratio, I can work it out the hard way but any information would be useful

Thanks in advance

[mowgli]

there wasn't a magazine article on how to do this Royston. there were a few pics (and some bullsh!t from PMC) in a couple of mags, but that was it.
when i did mine, i actually used a vernier to measure the pmc mag pics & scaled them up to get a decent idea of what needed removing from the dishes.

[thanks to bazzap8389]
http://i660.photobucket.com/albums/uu329/bazzap8389/B260DE94-B2A3-4879-A1E1-04401F904BE3_zpswtt0t9ux.jpg

[mowgli]

from memory, i used the original line of the dish as a start point, and i took it down about 5mm, with a radius on the edges.
it was in 1989 or thereabouts, so forgive me for being a bit hazy. i was aiming for 10.5:1cr.

i did end up doing the old fashioned method of actually measuring everything. i used perspex, cooking oil & an old pig syringe (my dad kept them) to measure the head cc, maths to do the gasket & bore volumes and then calculated what the piston top cc needed to be.

the one thing i remember most was the machinist refusing to accept payment for the piston machining as he was convinced it would blow up when i ran it.. lol

[mowgli]

oh & as it was november, i built the engine up on my bedroom floor...... one of the daftest things i ever did with metal. it was sodding heavy to get down the stairs on my own

[Royston]

Thanks Mowgli, its a great start! You can see the depth of the piston crowns!

My SR has a PMC 32/24 DMTL weber conversion for years

[Andy]

Ya lucky you didnt go through the ceiling you silly sod lol

[mowgli]

my mum nearly did when she came home from slimming world & found me putting the sump pan on.

[Jonesfach]

my mum nearly did when she came home from slimming world & found me putting the sump pan on.

Class....

[mowgli]

sorry, my mistake... her slimming world class

[Royston]

Can anyone confirm that 1.2/1.3 are the same part number, combustion chamber size please.


Combustion chamber and piston crown volume(inc gasket) on 1.2 is 36.46cc and for the 1.3 it is 39.54cc working on 9.2:1 std CR

The swept volume for 1.2 is 299.02cc

The swept volume for 1.3 is 324.27cc

The swept volume for 1.4 is 348.9cc

From my rough calculations the comp ratio for 1.2 pistons/1.3 crank and conrods is 10.57:1 calc (348.9cc + 36.46cc)/36.46cc

assuming the 36.46 cc combustion chamber/piston crown (and gasket)


Will need to confirm though

Here are a few pics of the pistons 1.2 left, 1.3 +0.5mm right
http://img.photobucket.com/albums/v697/1297cc/DSCF7969_zpse36bc677.jpg

Underside
http://img.photobucket.com/albums/v697/1297cc/DSCF7972_zpsd1203062.jpg

Difference on piston crown
http://img.photobucket.com/albums/v697/1297cc/DSCF7971_zps2e52132c.jpg

Engine details, if you want to have ago with the sums!
http://img.photobucket.com/albums/v697/1297cc/DSCF7973_zps1f75e452.jpg

[mowgli]

to get cr, it is
[head cc + piston crown cc + gasket cc+ swept volume]/[head cc + piston crown cc + gasket cc].

the swept volume for the 1.4 would be 348.935cm2

the gasket cc is 47.78x the thickness of the gasket in cm

[Royston]

the gasket cc is 47.78x the thickness of the gasket in cm

I will need to do this properly as you did Mowgli, I have just gone over the rough figures and I had made a mistake but the CR works out at 10.57:1 this is theoretical

[Royston]

The combustion chamber/piston crown/gasket volume was estimated by the following

Std comp ratio 1.2 and 1.3 is 9.2:1

Swept volume is 8.2 of the 9.2:1 cr and the combustion chamber size is 1

Therefore by calculation

The swept volume for 1.2 is 299.02cc (8.2)

Combustion chamber and piston crown volume(inc gasket) on 1.2 is 36.46cc (299.02/8.2)

The swept volume for 1.3 is 324.27cc (8.2)

Combustion chamber and piston crown volume(inc gasket) for the 1.3 it is 39.54cc (324.27/8.2)

I think I got it right nowlol

[_Jake]

i did this using a different block (x14sz) which sat the pistons flush with the deck, with a c16se head it worked out 12.5:1 i was planning to run it with a long dur high lift cam and tb's but had a go in an evo and now im building a turbo engine lol

[jimbob-mcgrew]

theres various ways to measure the CR, but i think its easiest, and least complicated, to just do it the oldskool way, and measure everything in liquid cc's, and calculate the CR using the divided formula.

id take measurements of everything as stock, then you know exactly how much needs to be taken away to get the CR your aiming for

[Jonesfach]

So are you going to go with the 1.2 Pistons and bore it out bit more?

[Royston]

So are you going to go with the 1.2 Pistons and bore it out bit more?

Looks like that is the plan currently, need to establish if I need to machine the pistons to reduce CR, need to check there is sufficient material in the liners (suspect there is)

My SR has +0.5mm pistons (75.5mm) that equate to @ 1330cc the 1.2 pistons (77.8mm) work out at 1389cc

[therealnovaboy]

so long as the cc of the head and head and gasket is the same between the 1.2 and 1.3 then theoretically this is correct as the piston crowns have a different cc.

if the con rods are the same length between the engines then it is wrong as the different stroke will mean the piston compression height is different between the engines.

when you fit the 1.2 piston to the 1.3 rod it would then change your theoretical CR

[Royston]

so long as the cc of the head and head and gasket is the same between the 1.2 and 1.3 then theoretically this is correct as the piston crowns have a different cc.

if the con rods are the same length between the engines then it is wrong as the different stroke will mean the piston compression height is different between the engines

when you fit the 1.2 piston to the 1.3 rod it would then change your theoretical CR



Thank for the input,

I do not know if the conrods are common between the engines, but I am confused over the different in compression heights, the stroke is the stroke, hence swept volume.

The measurement between the piston crown to the gudgeon pin centreline on both pistons is the same, and therefore will be in the correct TDC height, (compression height??) in the 1.3 block

I do have a complete 1.2 8V engine, might need to check that the combustion chamber in the heads are the same/similar

[mowgli]

royston, as long as the block hasn't been decked, the 1200 piston height is the same as the 1300 piston, ie. flush to the top of the block

use the 1.3 conrods

i used both a 1200 head & a 1300 head on mine & there was no noticeable difference in performance.


i did the piston crown calculation based on what i needed it to be, then drew a little cross section plan for the engineer to work to.

if you can measure your old gasket thickness, i'll have a crack at the numbers

do you have a hydraulic press? cos it makes gudgeon pin swapping a lot easier. i used an old gudgeon pin, ground down, with a bolt up the inside as a press to help get the new pins back in. people always say it is better to put the pins in the freezer & the rods in the oven, but i can't imagine this actually went on in a gm factory in 1984. and its a sod to do if your oven & workshop are any distance apart.

[therealnovaboy]

i had a think over lunch and the first calc for compression volume is right. as you have calculated it for a seperate 1.2 and 1.3 engine. I had it in my head you were using the same stroke but a different bore.

if the compression height of the pistons are the same and then the rod is different as the stroke is shorter on the 1.2. in which case you are ok if you use the rod common to the crank.

i measured a used gasket the other day at 1.35mm i can confirm later when i get my phone.

[jimbob-mcgrew]

didnt you have to shave approx 4 or 5mm off the piston tops, for yours mo ?

[mowgli]

It was something like that. It was 25 odd years ago

[therealnovaboy]

Ok this may be nonsense but bare with me.


providing the compression height, head cc, stroke and gasket is the same and the both piston crowns are flush with the top of the block. You could get a tray of water with let's say the depth to the first ring on the piston and of a known weight/volume. If you place the 1.3 piston crown down in it and measure the displacement volume of the water and add it to the displacement of the cylinder. Do the same with the 1.2 piston and add the displacement of a cylinder with a 1.2 piston and a 1.3 stroke. subtract these two volumes it would equal the volume you would need to remove from the 1.2 piston to get the same CR as a standard 1.3.

To work out how much to skim off the piston lower it into the same volume of water until it's displaced the difference of volume from before. The distance you have lowered it into the water to displace the right volume would be the height to skim off the piston.

[Royston]

Thanks for the info, I see what you mean.

My aim is to raise the CR up to as high as I can get away with, @ 10:1 preferably without machining the pistons as long as I can get away with pump fuel (super unleaded)

I will be using 1.3 conrods and crank, the block hasn't been decked and wont be as I don't want to remove the original engine number

[mowgli]

i'll sit down later & thrash outr the numbers to see what i get. is that cc for the heads measured or gleaned from elsewhere?

[Royston]

i'll sit down later & thrash outr the numbers to see what i get. is that cc for the heads measured or gleaned from elsewhere?

I have back calculated it using the 9.2 CR against the swept volume.

I will check the volumes the right way, when I get chance.....

[Royston]

Located my spare 1.2 head to compare with the 1.3

Both are early heads, cathederal ports and cast in 83 and 84 respectively, valve sizes are identical

33mm inlet, 29mm exhaust

1.2 part number R90090541
http://img.photobucket.com/albums/v697/1297cc/DSCF8038_zpsdfef9540.jpg

1.3 part number R90090546
http://img.photobucket.com/albums/v697/1297cc/DSCF8037_zps36de1f6a.jpg

The combustion chambers are different volumes and shape, I will need to check them properly, soon
Visually the 1.2 combustion chamber looks to have a smaller volume that the 1.3, both are about the same depth, valves are at the same height.

A few pics

1.2
http://img.photobucket.com/albums/v697/1297cc/DSCF8042_zps0cce0e6f.jpg

1.3
http://img.photobucket.com/albums/v697/1297cc/DSCF8043_zps7a5a4aa9.jpg

Might be useful for someone else;)

[_Jake]

is anyone gonna sticky some info on this? i put it up when i did mine and still people ask and spout **** about it.....

[Royston]

I'll stick more info in as I go, someone in admin might sticky it for future reference..................

[mowgli]

it needs a how to, once the job has been completed.

[Royston]

it needs a how to, once the job has been completed.

I'll pen once we're sorted;)

[mowgli]

have you got the head cc's measured yet?

[Jonesfach]

have you got the head cc's measured yet?
I doubt it....have you seen the state of the one that's come off?
Theirs a pic on the WIP thread.

[Royston]

have you got the head cc's measured yet?

No but soon.....

[turbojolt]

is anyone gonna sticky some info on this? i put it up when i did mine and still people ask and spout **** about it.....

I wouldn't like anything sticky'ed based on half a engine build that's never seen the road :p

[_Jake]

I wouldn't like anything sticky'ed based on half a engine build that's never seen the road :p

lol dont sticky anything about yours then!! least i got up and did it.

[turbojolt]

I would rather my bodges wasnt stickied lol

[jimbob-mcgrew]

yeah, would be be good if you could stick up the cc volumes, whenever you get round to it royston :thumb:

i dont know how accurate these figures are... but i got this info from somewhere a while back :

12ST = 130 cc
13S = 140.97 cc

[mowgli]

i haven't a clue what those figures refer to, but compressed cc is way smaller than that.

[jimbob-mcgrew]

i dunno... im stupid

[mowgli]

if a 1300 cc engine has 9:1 compression, then the unswept+swept cc's must be 9 times more than the unswept cc's. 140+325= 465 465/140 is about 3.3

[Royston]

Made a little progress this week, at last the 50 ml burette finally arrived this week, need to knock up a stand for it, hopefully may get some measurements this weekend!!

[mowgli]

woohoo

[Royston]

Been busy today, I have CC'd the following which maybe useful.....

1.2 Cylinder head gasket volume (78.8 mm dia *1.3mm thick) = 6.34cc

1.3 Cylinder head gasket volume (76.0 mm dia *1.3mm thick) = 5.90cc

1.2 Piston Crown volume = 10.4cc

1.3 Piston Crown volume (was a +0.5mm oversize) = 15.3cc

Therefore a 4.9cc difference!

1.2 Cylinder head chamber volume, with valves and spark plug = 18.6cc

1.3 Cylinder head chamber volume, with valves and spark plug = 19.6cc


Therefore a 1cc difference

So now I have the correct volumes

The Compression ratio on a 1.3 engine bored to suit unmodified 1.2 pistons with a 1.3 head will be....

1.3 Head volume = 19.6cc

1.2 Head gasket = 6.34cc

1.2 piston = 10.4cc

which equated to 36.34cc

Swept volume is 348.9cc

Compression ratio equates to 10.6:1 (348.9cc + 36.34cc)/36.34cc

Using the 1.2 head results in a compression ratio of 10.87@1

[garyc]

that assumes your pistons are flush with the top of the block, I have yet to see one that is. our race rules permit 10thou out the top of the block so you may want to take that into concideration.

[Royston]

that assumes your pistons are flush with the top of the block, I have yet to see one that is. our race rules permit 10thou out the top of the block so you may want to take that into concideration.

Yes, you are correct, unfortunately I dont have that info available, I might reassemble the crank and pistons and measure it with some feeler gauges.

Thank you for the pointer, they "felt pretty flush" but will double check

[mowgli]

mine were flush. i guess i was lucky.

i really wish i'd actually kept all my calcs for this conversion, but in the pre internet days, when i devoured CCC mags, as no doubt you did too, i assumed, stuck in my little outpost of the empire (leicestershire) that loads of other people were doing the same as i was....i was wrong

[tothemark]

I know that this is an old thread, but rather than start a new on based on a similar project i thought it best to add to it, so no flaming :cool:

I have now sourced some new Mahle 1200ST pistons, (77.8) in standard size and also a set in plus .5 (78.3) and so will probably go down the 1300 block rebore route ignoring my concerns about bore flex.

Working on Roystons figures with my two cylinder heads i have the following, using 1200 pistons, 1300 crank and rods, 1300 block bored out;


Both of these heads have been skimmed previously, hence the low chamber volumes.

1300 head 35/29 inlet outlet
Gasket 6.3mm, chamber 13cc, Piston crown 10.4, swept volume of 1200cc std =348.90/29.7 CR 11.747
Gasket 6.3mm, chamber 13cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/30.22 CR 12.122

C14SE head 38/33 inlet outlet
Gasket 6.3mm, chamber 16cc, Piston crown 10.4, swept volume of 1200cc std =348.90/32.7 CR 10.66
Gasket 6.3mm, chamber 16cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/33.22 CR 11.02


Using my enem Y24, duration 292/107/12.0/2 i am unsure as to whether my clearance tolerances will be ok assuming the block hasnt been decked, can anyone calc that cos i have exhausted my maths capability now.

Dont know if the blocks have been decked, is there a datum point i can use to check ? Cos this will throw a new variable into it.

[Royston]

If the original engine number is present, block wont have been decked.

iirc std 1.3 inlets valves are 33mm, I run 38mm inlets and 31mm exhaust in my 1.3 SR ported head

Will need to have a think about clearances with the cam, are you running solid lifters? I suspect there is enough clearance

[tothemark]

If the original engine number is present, block wont have been decked.

iirc std 1.3 inlets valves are 33mm, I run 38mm inlets and 31mm exhaust in my 1.3 SR ported head

Will need to have a think about clearances with the cam, are you running solid lifters? I suspect there is enough clearance


Yah, solid lifters for sure, did you have to enlarge the valve pockets in the 1200 pistons to accommodate your bigger valves ?

Ill check for an engine number, must admit i havent seen one, so whats the best way to measure the deck ? i dont have a haynes so dont know the original height either.

The c14se head looks like its had 1mm off it dropping from a 21cc to 16cc combustion.
With my 1300 head at 13cc its had a very generous 1mm off as well.

[Royston]

I did enlarge the diameter of the pockets on my 1.3 so that they were @ 1mm larger than the valves.

What is the engine to be used for?

[tothemark]

Had a look at the two blocks, the spare red block still has part of a stamp on it see link :

http://i614.photobucket.com/albums/tt222/tothemark2003/20150813_215858_zpsgxhffpyo.jpg?t=1439414817

so i am presuming it's original form, possibly bore out +50 as it came with a set of spare pistons, had to enclose a photo of them to show the level of butchering thats been done to them (not by me) Black and decker special.

[tothemark]

This is the butchering
http://i614.photobucket.com/albums/tt222/tothemark2003/20150808_185742_zps6lqzqfsp.jpg?t=1439415604


Anyway the main race block i want to use looks like its been decked ;

http://i614.photobucket.com/albums/tt222/tothemark2003/20150813_220145_zpst0ahsl8h.jpg?t=1439415604

http://i614.photobucket.com/albums/tt222/tothemark2003/20150813_220335_zps4yl1q7qb.jpg?t=1439415601

If anyone has the block sizes and where the measurement is taken from it will be a great help to me.

Many thx TTM

[Royston]

The only way you can assess is to refit the crank an pistons and measure, if possible. (will need a depth micrometer, could get away with feeler gauges and straight edge)

Is there a max limit for piston protrusion above the deck height?

The spare engine I built for my second sport ended up with the pistons being @ 15 thou above the deck height. (was @ 25 thou below before decking, std unmachined block with engine number present)

[tothemark]

The only way you can assess is to refit the crank an pistons and measure, if possible. (will need a depth micrometer, could get away with feeler gauges and straight edge)

Is there a max limit for piston protrusion above the deck height?

The spare engine I built for my second sport ended up with the pistons being @ 15 thou above the deck height. (was @ 25 thou below before decking, std unmachined block with engine number present)


hi Royston,

I suppose the max height is determined by the compression i want, dont want it to be more than 11 to 11.5 cr max.

I have a spare 1300 rod that i will machine out the gudgeon slightly to allow a new piston to be built onto it which will facilitate easy removal later and then build the engine/s up and work out the figures, check clearance and valve pocket sizing etc.

Now just have to wait for the pistons that a mate is picking up whilst on holiday abroad, i hope he isnt flying easyjet..

TBC

TTM

[tothemark]

I didnt fancy sitting around so I have done a measurement on the basis that the red block with the engine vin code is a good template for measuring the original deck height of a standard block.
Measuring from both sides of the bearing carrier to the top of the block i have a difference, in that the race block is 1mm lower, i think its pretty safe to assume thats what its been decked by in order to make some further calcs at this stage.

1300 head 35/29 inlet outlet red block standard
Gasket 6.3mm, chamber 13cc, Piston crown 10.4, swept volume of 1200cc std =348.90/29.7 CR 11.747
Gasket 6.3mm, chamber 13cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/30.22 CR 12.122

C14SE head 38/33 inlet outlet red block standard
Gasket 6.3mm, chamber 16cc, Piston crown 10.4, swept volume of 1200cc std =348.90/32.7 CR 10.66
Gasket 6.3mm, chamber 16cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/33.22 CR 11.02

1300 head 35/29 inlet outlet race block
Gasket 6.3mm, chamber 13cc, Piston crown 10.4, swept volume of 1200cc std =348.90/28.7 CR 12.18 allowing for 1mm decking
Gasket 6.3mm, chamber 13cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/29.22 CR 12.53 allowing for 1mm decking

C14SE head 38/33 inlet outlet race block
Gasket 6.3mm, chamber 16cc, Piston crown 10.4, swept volume of 1200cc std =348.90/31.7 CR 11.00 allowing for 1mm decking
Gasket 6.3mm, chamber 16cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/32.22 CR 11.37 allowing for 1mm decking

This has been a good exercise to determine a starting point as to what fits with what, bearing in mind i had no history of the parts i have.

Looks like the the highlighted options are the two configurations i can build, not too happy with 11.74, but its a really nicely worked head, so i dont want to discard it.

Are there any thicker head gaskets (thicker than 6.3mm) that i can use, i presume the Payen is 6.3mm, to bring the compression down on my 1300 head configuration ?

Many thanks
TTM

[Royston]

I have my original 1.3 sport block, and head, I could take measurements for you, also I don't live too far away, you could call with your parts and compare side by side, that's another option.

Compressed head gasket I have measured is 1.3mm thk, (6.3mm" area)

[Balley]

I didnt fancy sitting around so I have done a measurement on the basis that the red block with the engine vin code is a good template for measuring the original deck height of a standard block.
Measuring from both sides of the bearing carrier to the top of the block i have a difference, in that the race block is 1mm lower, i think its pretty safe to assume thats what its been decked by in order to make some further calcs at this stage.

1300 head 35/29 inlet outlet red block standard
Gasket 6.3mm, chamber 13cc, Piston crown 10.4, swept volume of 1200cc std =348.90/29.7 CR 11.747
Gasket 6.3mm, chamber 13cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/30.22 CR 12.122

C14SE head 38/33 inlet outlet red block standard
Gasket 6.3mm, chamber 16cc, Piston crown 10.4, swept volume of 1200cc std =348.90/32.7 CR 10.66
Gasket 6.3mm, chamber 16cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/33.22 CR 11.02

1300 head 35/29 inlet outlet race block
Gasket 6.3mm, chamber 13cc, Piston crown 10.4, swept volume of 1200cc std =348.90/28.7 CR 12.18 allowing for 1mm decking
Gasket 6.3mm, chamber 13cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/29.22 CR 12.53 allowing for 1mm decking

C14SE head 38/33 inlet outlet race block
Gasket 6.3mm, chamber 16cc, Piston crown 10.4, swept volume of 1200cc std =348.90/31.7 CR 11.00 allowing for 1mm decking
Gasket 6.3mm, chamber 16cc, Piston crown 10.92 swept volume of 1200+.5 =366.35/32.22 CR 11.37 allowing for 1mm decking

This has been a good exercise to determine a starting point as to what fits with what, bearing in mind i had no history of the parts i have.

Looks like the the highlighted options are the two configurations i can build, not too happy with 11.74, but its a really nicely worked head, so i dont want to discard it.

Are there any thicker head gaskets (thicker than 6.3mm) that i can use, i presume the Payen is 6.3mm, to bring the compression down on my 1300 head configuration ?

Many thanks
TTM

Could you not use a decompression plate, or is a there some kind of multi layer steel gasket available you could use?

[tothemark]

I have my original 1.3 sport block, and head, I could take measurements for you, also I don't live too far away, you could call with your parts and compare side by side, that's another option.

Compressed head gasket I have measured is 1.3mm thk, (6.3mm" area)


Thx for the offer Royston, im sure my red block is standard, my crank is out so i measured from the main bearing carrier, cant remember the figures but will do again.

Hi Balley, id love to have a Cometic 1.7mm head gasket but they only seem to do them for a 16v, a compression plate thx for jogging me on that ive just emailed profileman on ebay as his 3mm ally one would allow me to get 11.0 on each engine just by swapping the piston configurations - now that would be a result ! Fingers crossed he does one, i'll let you know.

[Balley]

Spot on, fingers crossed for you.

[garyc]

look for a head gasket for a 13N engine, it is the same size but slightly thicker ast std. I think I have one at home somewhere.

[tothemark]

Hi Gary,

Whats the diameter, im boring out to 78.3, i would have thought the 13n head gasket will be too small.

Struggling to get a compression plate so i may just recalc the pocketing of the pistons to accommodate the cr required.

[garyc]

get a HG made there are places that make them to varying thicknesses. iirc they are about £100, got to be easier than machining pistons......