Engine Rebuild - Parts Questions (many)

[Asroc66]

OK
Here we go
For the record I am not a mechanic but this is what I know and have run successfully (note Race mechanic checking my work at each step +/- input).

Cheapest option - machine and refit existing pistons and rods with new rings - my feeling is false economy, why not save a little more and upgrade!
Average option - buy Gemini G160 dished pistons (Duralites/Hepalites? if you can find them but ACL went belly up and sold all its hardware to China) and standard 1600 rods - compression ratio approx 9.2:1 with 82mm bore. If in doubt pick up your standard rod and piston assembly in one hand and the Gemini in the other then proceed to throw the standard >40 year old stuff over your shoulder and in the bin.

What I did before turboing Asroc- Bore to G180 84mm, dished cast gemini pistion on standard 1600cc (75mm) rods - compression ratio approx 9.5:1

Captain high cash option - Custom Forged Pistons from CP in America who make the pistons for NASCAR, V8 Supercars, Drag etc etc and go for gold on standard 1600cc rods. Refer earlier statement about using origional rods! (not much change from 12 Large)

re Cam bearing - I do recall one required filling to clear the lobe, I thought it was the 6th from the front ? inlet

Re resistance to turn (I cannot remember the term, something along the line of lannish???) - aka Machine/sand down the CAM journals to match each bearing not reducing inner bearing diameter. Stick a torque wrench on the end of the cam and turn to speck. Close to Datsun as they copied Isuzu right?

ALWAYS have a full balance done including harmonic balancer and flywheel with clutch fitted - ALWAYS
A balanced motor is a happy reliable fast motor.

Hope this helps

[Glenn]

OK
Here we go
For the record I am not a mechanic but this is what I know and have run successfully (note Race mechanic checking my work at each step +/- input).

Cheapest option - machine and refit existing pistons and rods with new rings - my feeling is false economy, why not save a little more and upgrade!
Average option - buy Gemini G160 dished pistons (Hepalites if you can find them but ACL went belly up and sold all its hardware to China) and standard 1600 rods - compression ratio approx 9.2:1 with 82mm bore. If in doubt pick up your standard rod and piston assembly in one hand and the Gemini in the other then proceed to throw the standard >40 year old stuff over your shoulder and in the bin.

What I did before turboing Asroc- Bore to G180 84mm, dished cast gemini pistion on standard 1600cc (75mm) rods - compression ratio approx 9.5:1

Captain high cash option - Custom Forged Pistons from CP in America who make the pistons for NASCAR, V8 Supercars, Drag etc etc and go for gold on standard 1600cc rods. Refer earlier statement about using origional rods! (not much change from 12 Large)

re Cam bearing - I do recall one required filling to clear the lobe, I thought it was the 6th from the front ? inlet

Re resistance to turn (I cannot remember the term, something along the line of lannish???) - aka Machine/sand down the CAM journals to match each bearing not reducing inner bearing diameter. Stick a torque wrench on the end of the cam and turn to speck. Close to Datsun as they copied Isuzu right?

ALWAYS have a full balance done including harmonic balancer and flywheel with clutch fitted - ALWAYS
A balanced motor is a happy reliable fast motor.

Hope this helps

Interesting info although what i found (ie the engine builder who cc'd my engine) when fitting +40 Gemini pistons and rods was the CR went down well below 9:1 mainly due to increased bore. Head then had to be machined to bring back to ~9.6:1 as I recall.

[degruch]

Were those standard flat top Gemini pistons though Glenn? James mentioned domed pistons.

I assume there's a number of high compression performance pistons available for Gemini's, not sure where to start (except at 1584cc's). Wasn't real keen on replacing the original pistons, since there's nothing wrong with them, but re-sleeving at 81.5mm is now looking like $800+, same cost as (not real great quality) custom pistons and rings.

Probably blew my chance to check torque - cam and bearings are out now.

[Asroc66]

Hi
I cited dished not domed pistons
Flat tops would be OK too
If you use your old pistons you should machine the piston ring grooves as they wear out of square! then fit new custom rings. I have done this with nissan rings before
If you oversize a bore it will increase the compression (depending upon the piston dish used that is ie if you use flat tops pre and post the compression ratio should rise)
http://www.ford-trucks.com/forums/77198 ... ratio.html
this is just an example of raising and not the only reference, search the net they are all over it
Planning head is OK to a degree but you will eventually run out so dont get carried away
Pistons are cheap on ebay or your local machine shop so I wouldn't retain origional pistons - too heavy
Aluminium casting has come along way
even consider shaving skirts for less friction
Cheers
JD

[1968GT]

Interesting info although what i found (ie the engine builder who cc'd my engine) when fitting +40 Gemini pistons and rods was the CR went down well below 9:1 mainly due to increased bore. Head then had to be machined to bring back to ~9.6:1 as I recall.

Glenn, from the info you have sent me on the GT, what you are saying is correct, I have checked the info on those data sheets you sent me.
Dave M.

[Glenn]

Hi
I cited dished not domed pistons
Flat tops would be OK too
If you use your old pistons you should machine the piston ring grooves as they wear out of square! then fit new custom rings. I have done this with nissan rings before
If you oversize a bore it will increase the compression (depending upon the piston dish used that is ie if you use flat tops pre and post the compression ratio should rise)
http://www.ford-trucks.com/forums/77198 ... ratio.html
this is just an example of raising and not the only reference, search the net they are all over it
Planning head is OK to a degree but you will eventually run out so dont get carried away
Pistons are cheap on ebay or your local machine shop so I wouldn't retain origional pistons - too heavy
Aluminium casting has come along way
even consider shaving skirts for less friction
Cheers
JD

looks like you are right..my memory is not.... it must be that the Gemini pistons have a lower crown than std Bellett. GT's have a weird piston top shape. That would account for it, not the overbore.
Is there a 'choice' of Gemini piston flat or domed ? I would have thought all Gemini engines were the same although polution control later, may have changed that.
I heard its getting harder to find new Gemini pistons these days...... I doubt they are making runs of them anymore, its just finding somebody with actual stock on hand.
Getting CR back up again, only the head to plane mostly in a practical sense?

[Asroc66]

I find this topic really interesting and have spent a lot of time researching while building Asroc
Re gemini pistons I believe you can get flat top and dished (std and turbo engines) but dommed are special order (aftermarket).
Mostly dished though on the net
Gemini is Cross flow motor anyway so no good for Bellett valves
J

[Glenn]

I find this topic really interesting and have spent a lot of time researching while building Asroc
Re gemini pistons I believe you can get flat top and dished (std and turbo engines) but dommed are special order (aftermarket).
Mostly dished though on the net
Gemini is Cross flow motor anyway so no good for Bellett valves
J

I can't imagine what turbo engine pistons you could get for Gemini ex factory ? Aftermarket perhaps.
Way back, I had a Piazza 2litre turbo engine i set up to go in a Bellett. (not a simple conversion, especially with intercooler.) Have no idea of piston size etc but new factory pistons were $600 a set in those days....... i decided to sell the motor and stop the project.

[degruch]

Flat tops are easy to find - eBay, Gumtree, Repco, etc. Can't find much online for dished, unless they're a G200 piston...are they of any use in a 1584cc car?

All in all, if I need to resleeve I may as well keep the original pistons and pay the megabucks for sleeves...the pistons are free after all! If I can find oversize Gemmy flat top pistons to suit, looks like I'll go that path. Time and money is running out.

[Asroc66]

Hi
Do any of these help

G160/161
http://www.ebay.com.au/itm/JCC-pistons- ... 203wt_1362

http://www.ebay.com.au/itm/New-Holden-G ... 050wt_1124

G180
http://www.ebay.com.au/itm/PISTON-SET-4 ... 120wt_1124

http://www.ebay.com.au/itm/G180Z-1-8-IS ... 58921465ff

http://www.ebay.com.au/itm/76-85-Fits-G ... 555wt_1124

J

[degruch]

Cheers James, they're already on the watch list...not going for 1800cc though, so only looking at standard Gemmy pistons.

[Glenn]

Cheers James, they're already on the watch list...not going for 1800cc though, so only looking at standard Gemmy pistons.

I think the blocks are way too different from OHV to SOHC ? Otherwise, an OHV on an 1800 SOHC block would make a nice boost.

[Asroc66]

Hi Glenn
I have to agree with you on that one

The SOHC is torqy, but im my humble opinion a well built, bored and balanced G161 is far more bang for your buck
Cheers
JD

[Glenn]

Hi Glenn
I have to agree with you on that one

The SOHC is torqy, but im my humble opinion a well built, bored and balanced G161 is far more bang for your buck
Cheers
JD

so a well built, bored and balanced SOHC 1800 should be even more bang for your buck? If you have a block to start with though.

[Asroc66]

Well thats a good question

The G180ss has effectively 2 cams - the OHC one of course and the origional OHV one to drive the dizzy, fuel and old pumps. So 2 timing chains, 4 sprockets, numerous chain guides etc etc oh yea is heavier and taller thus affecting handling too

So the G161 OHV with 1800cc pistons is very tempting.

As my mechanic says, re push rod engines....... "If its good enough for Nascar its good enough for me" revving > 8000 rpm

JD

[Glenn]

Well thats a good question

The G180ss has effectively 2 cams - the OHV one of course and the origional one to drive the dizzy, fuel and old pumps. So 2 timing chains, 4 sprockets, numerous chain guides etc etc oh yea is heavier and taller thus affecting handling too

So the G161 with 1800cc pistons is very tempting.

As my mechanic says, "If its good enough for Nascar its good enough for me" revving > 8000 rpm

JD

yes, a lot of bits in a SOHC... interesting too, I saw somewhere that the Bellett has 53 : 47 weight distribution.
I prefer low end grunt myself, makes a much more drivable car.

84mm would be a very large over bore of a GT engine.... is it possible ? (Gives about 1663cc capacity)

[Asroc66]

That's what I am running is Asroc though had the block sleeved just in case
J

[degruch]

Progress: Body and engine united in the one location, engine ready for assembly, but...

...no water pump! Won't be getting the car back in the foreseeable future as a result. Very frustrating.



On the positive side, cam bearings worked a treat.

[Asroc66]

Very Happy to hear the cam bearings worked
Well they worked for me so why not hey'

Good luck with the water pump
Rare as gold encrusted unicorn poooo

If u find some please grab one for me!!!!!


Cheers

[mrflibbles]

could you use an electric water pump?