Hey fellas,
New member here but not-so-new to these engines [I'm one of the dreaded Gemini crew]. Although I have had one of these engines before all I did was tune/drive it and blow it up about 6months later
After a brief hiatus with a turbo'd SOHC ive got my hands on another twin cam and am starting a full rebuild. What im trying to do is get all my eggs in the one basket so to speak - although I wont be starting on the engine for another month or so, i want to be able to source all the parts etc that I need first prior to starting.
So what ive got is a G180w ex-PF60E - front and down oil filter, later rocker cover version - in about 10,000 pieces atm. Initial inspection says I should be able to reuse the pistons and the bores can be honed-only. The following is a brief run down on what Ill be doing, followed by what I need some help with.
-Rebuild using G200z big ends and G180z/G200z main bearings
-G180z piston rings
-Headgasket reused as it looks fine and i know how hard these are to come by, especially a graphite one as this is
-Water pump etc all look like they are in reusable shape
Engine came sans-cams and gears [since sourced both], inlet manifold [will be making one so moot point] and distributor [will most likely be going CAS off the crank pulley]. Inlet will be 4 x 45mm throttle bodies [have these, ex-RB26 GTR] with the injectors placed as close to the butterfly as possible. Already have 4-1 extractors for it - just need to hope they clear the engine mounts - typical of DOHC-on-petrol-xmember-in-gem saga. Now, if your still with me after my incoherent rambling, the areas I much need assistance/clarification on are as follows:
-Cam grinds. Looking at getting the cams reground so a pointer towards specs or someone that knows these engines would be much appreciated. Being quite scarce, most people Ive spoken to have no idea about these engines so getting some good advice is proving difficult. What I would like is to enhance the power between 4000-7500rpm - dont really want to go over 8000rpm as the gearing becomes an issue. Those that know Geminis well know that its virtually impossible to change the final drive in the diff short of going an all out diff conversion. Ive been told to look at 2TG's and 18RG's for cam grind/spec ideas, but knowing how crap Toyo engines are and seeing as most Toyo owners, particularly stateside are chequebook warriors [ie they order the parts and dont know jack about the specs] im finding this difficult too.
-The head itself. I know these flow alot better then the SOHC one, and they work alot better then the specs suggest. Are there any real hinderances/restrictions and should I look at getting it ported? Ie - do they have a design flaw that causes them to run out of breath at anything over 100rwkw. I suppose i could measure the valves easily enough, but are they the same as the big-port G series SOHC?
-Cam bearings look serviceable/reuseable so they should be ok, especially considering I cant find new ones. Is there a source for these that im just too stupid to find? Also, whats the go with the valve seal/brass-ish looking collet? Anywhere these can be found? Havent checked to see if it actually IS leaking past the valves but replacing these items would be just common sense.
-Timing chains. Obiouvsly there are two sets, am i right to assume the lower chain [crank to dummy/pushrod cam] is the same as the pushrod G series ex-Bellett? According to this ->
viewtopic.php?f=40&t=1446 , that would mean I want 5114 038 or S114 098, to suit a Hillman? Saw this on one of the build threads:
Quote:
A forum has the recipe to convert mitsubishi timing chain and tesioner to suit.
Does anyone have more info on this? Id assume 'that' Mitsu engine would be the Astron as these run a double row chain as per dohcs.
-Pistons. I know G series SOHC's can be dropped in however these would
lower the CR which is not what Im after. Have heard rumours of toyo 2T pistons being able to be dropped in. Not sure if these were the 2TC or 2TG items - old mates memory was abit how-ya-goin. Any ideas as to wether this is doable [can still get 2T pistons aftermarket, same cant be said for the Isuzu DOHCS] or if there are any alternatives? Abit of a bump in CR wouldnt go astray.
-Inlet flanges. Anyone know anyone making these up?
Think thats about it although there will most likely be more. As an iside heres the last DOHC i had:
Was a bone-standard G200w that I modified to take a VN-S V6 throttle body, also had crap 4-2-1 extractors [trust me, they were attrocious] and an as-old-as-time-itself Haltech E6K Ecu. Made 82rwkw which was enough to send S2000's home!
We have had to use second hand parts in the past 1 engine needed a piston the other needed a inlet valve. Being a gemini man i would assume you know or know of elky he has supplied second hand bits in the past. To my knowledge cam bearings are not available be carefull with them. Sump gaskets are hard to find also but you gan get around this or buy the set that Glenn speaks of. There is a gasket that goes between the head and the timing cover be carefull with this one also it has to compressed with the head gasket so thickness is important.
Had a chat with him about it, he promised to pass on the details to his "go to" man in his service department. Mentioned this to our receptionist at work, the name Phil Brock came up [the ZZ/R Gemini he raced at bathurst] when our lovel accountant Dina piped up and mentioned she does his book keeping! 
Just got off the phone to AAA Gaskets and your right it does exist sooooo going to order one now.
trade there is room to move 
