Engine Rebuild
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Thread: Engine Rebuild

  1. #1
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    Engine Rebuild

    Hi there,

    I have been reading a LOT of rebuild and mods on here and I was just hoping to check in w/ the experts on what I am thinking of doing. My engine has been giving me trouble (oil in the cylinder). I thought it was likely valve stem seals and that was not it. I had the head looked at professionally. I thought about buying a used engine from someone on here too, which is still an option. But, knowing that my head is good I am thinking of rebuilding the short block now.

    I already have put on:
    • Pertronix
    • New fuel pump and carb
    • New water pump
    • New timing chain and tensioner


    I am thinking about having the block bored to accept either:


    I am also going to have the rods reconditioned and the crank turned, if needed. I will install all new bearings and new freeze plugs.

    So my question is... are there any other modifications required to install 2.0L pistons in a 1.9 block with stock crank, head, cam, etc? Such as, will the wrist pin fit, valve clearance, etc?

    1970 GT 1.9S

    Thanks everyone!

    ~Josh
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    Project 1450 supporter... Site Supporter RallyBob's Avatar
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    Quote Originally Posted by jthorny1337 View Post

    So my question is... are there any other modifications required to install 2.0L pistons in a 1.9 block with stock crank, head, cam, etc? Such as, will the wrist pin fit, valve clearance, etc?

    1970 GT 1.9S

    Thanks everyone!

    ~Josh
    I think you’ll find the Wossners use a 22 mm pin, while the stock rods and pistons are 23 mm.

    This leaves three options:

    >have the pistons pin holes bored and honed from 22 to 23 mm

    >bore out the small end of the stock rods for a bronze bushing with 22 mm ID

    >buy aftermarket billet rods (most have a 22 mm pin bore)


    Also, a true 10.5:1 compression is a bit much for pump gas unless you have a fairly aggressive camshaft to bleed off some cylinder pressure.
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    Since everything will be or is apart, why not go with the 2.0 valves to go with the 2.0 pistons?
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    Hi RallyBob. I have read through MANY of your posts and you really have a lot of good info out there. Thank you for sharing all of that on the forums. It really helps guys like me who are still new to the Opel world.

    I had considered the pump gas issue and I am torn on it.. I probably won't drive it cross country so for around town or weekend trips to the mountains maybe the extra power is worth it (and the trouble of adding octane booster)? Some rough math with an online calculator, for what it is worth.. estimates 117 HP @ 10.5 and 106 @ 9.5. I don't think having them machine out the pin holes would be a big deal but maybe its just better to go w/ the OpelGT source stuff if that just fits. It is also a couple hundred dollars cheaper.

    I am considering upgrading to 2L valves too, Mike... but I don't really know what all that entails. I think Bob actually has a write up about that on here I read a while back.. I will try to find it again. Mostly I am just trying to get an egnine back on the road with as few of changes as possible and hoping that it runs well. I am worried that the more changes and modifications I make or have done, the less likely this thing is to run right. After ~6 years of restoring the car I am just ready to get it back on the road ya know...

    If I end up +$2K into this thing then maybe I should go with Bob's recipe for a 1.9 -> 2.4 (another great write up). But again... just worried I screw it up.
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    1000 Post Club Vincent's Avatar
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    I'll also advocate for 2 L pistons with 2 L valves.

    I ended up going with larger 45mm intakes valves from the 2.2 /2.4 engines when I built my 2L. Was alot more trouble but worth it!
    Last edited by Vincent; 3 Weeks Ago at 03:15 PM.
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    [QUOTE=RallyBob;1413853Also, a true 10.5:1 compression is a bit much for pump gas unless you have a fairly aggressive camshaft to bleed off some cylinder pressure.[/QUOTE]This is 100% spot on...... A true 10.5 will require you to have a larger cam to keep what is called dynamic compression ratio down to around 8:1 to run premium pump fuel. That applies even more so if your local premium is only 91 octane. And even then your tuning is going to have to be right, both for ignition timing and for fuel-air mixture. The penalty for getting this wrong is detonation, which possibly results in damaged/melted pistons and broken piston rings and lands. With the larger cams having a lot of overlap, then the idle will be rough and the very low RPM engine operation will lose a lot of torque. It's a lot safer for a 1st time builder to stick with a mid 9's compression ratio.

    As far as the larger valves, good upgrade. Just another thing to deal with before getting this going again.

    With the head check, did they check the valve guides to see if they were good (not worn)?

    Others may think differently, but I'll tell you that I never have had any of these stock rods reconditioned and still turned them to 8K RPM all the time in rally use. Never a rod problem or bearing wear issue, ever. Your HP level is modest; I was not running more than 125 HP.
    Last edited by Manta Rallier; 3 Weeks Ago at 03:45 PM.
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    It seems a simple and minor upgrade of the head seats done at your trusted machine shop, but of course you want to first ensure your cylinder head is not a late model 73 onward head that was prone to cracking around the valve seats. The info is buried here on this site about that issue.

    When the head has been magnafluxed and declared good, the machinist grinds bigger seats (not sure if new seat inserts go in.....that one is for Rally Bob or Manta.... Rallier to answer) while also ensuring your valve seats don't have excess play.

    Or you could inquire to OGTS for one of those 2.0 liter heads they once imported, had rebuilt. I think mine was 900-1000 for a complete, competition valve 3 angle seat job, 2 liter cylinder head already factory flowed in the intake and exhaust ports....

    OGTS carried hypereutectic 2.0 pistons and had a batch of Mahle 2.0 pistons a few seasons back. Worth a shot to ask if they are still available.

    Consider a 38 weber downdraft (again, OGTS), pertronix or crane cams electronic ignition and that is pretty much it; a basic overbored block fitted with a wee bit bigger pistons and the 2.0 spec valves to move that volume of gas mixture in and out of your motor as Opel designed it. Yes, 38 Weber cause your motor has more potential to take in a bit more gas, which gets you more power....

    My GT is a tired 73, low compression automatic with the crane cams electronic ignition and 32/36 weber, both parts I installed. Had a chance to drive a 2.0 powered GT with the automatic. Heavy duty MSD ignition. The power, when written down on paper here, is maybe 25 hp over my wheezing low compression car; which may not look like much here, but the difference in how it drove and sounded compared to my car was night and day. I believe it is the best power and value for buck. You get into those 2.4 hybrid motors out of a 1.9 or the factory 2.4's and you're looking at a heck of a lot more money.

    I believe Kyler Norman, here, has a 2.0 out of a 1.9 block, his with a single weber side draft, which increases the sex appeal and appearance. He has a lot of useful info available on how he tuned his car to perfection; including a slew of youtube videos worth subscribing.....
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  10. #8
    Über Genius First opel 1981's Avatar
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    If you're going high compression and/or high rpm, make sure you have forged rods, not cast ones.
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    OP, how do you plan to use and drive your engine/car? The reason to ask is to have some idea if larger valves will be of much use. I see a lot of posts around about HP, but realize that is peak HP up at higher RPM's at WOT. If you are only cruising and tooling around you are not really pushing the engine for peak HP, nor driving at WOT very much. In that case, the larger valves can be dispensed with IMHO. If you want to autocross or otherwise wind this thing out in spirited driving, then yes, the larger valves will be of value. But be ready to change the cam to take advantage of that..... once you start down the peak HP path, then everything may be on the table: manifolds, exhaust system, carb... etc.

    If you are mostly cruising around, then the best thing you are going to do with to bump the compression ratio up into the low-mid 9's. That is going to really boost your LOW RPM TORQUE, not peak HP. But in cruising and local driving around town, low RPM torque is what is of value to you. The 1.9 to 2.0 L change is good for that too.

    Bottom line: Don't do what the PO of my son's '65 Barracuda did. He took the 2 BBL 273 and replaced it with a 408 stroker, wanting more umph. When he sold the car less the stroker motor to my son, he said the stoker had ruined the car for his favorite uses: going for ice cream on a Saturday night with the wife and kids and cruising to local car meets. The stoker made it a too-powerful, tempermental beast, hard to drive smoothly. Some people want that; many don't.

    And... it is not hard to later pull the head, and make other changes to the induction and an exhaust, cam, etc.
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    Hi again. Thank you all for the help and advice.

    I plan on just cruising around and maybe making some weekend runs up to a mountain town. I live in the colorado front range, so torque to get up the mountain roads is more imporant than WOT racing for sure.

    I already have a 38 DGAS and pertronix ignition in the car so I guess I will just go w/ the 2L valves and 2L pistons since I am doing all of this. So far as I know my head is original to the car (1970). I think I will also just go w/ the OGTS 2L pistons since they seem like the easiest path forward and they fit.

    I just have a couple questions..
    • What parts should I order for the head conversion? My machinist told me that my valve stems were tight so would I just need new 2L valves, valve stem seals, and 2L valve seats?
      For the block do I just need 2L pistons and rings? I assume I can use my factory crank and rods?
      I do not know if it has a factory cam in it or not so I will probably just run that for awhile.
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  13. #11
    1000 Post Club Vincent's Avatar
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    Call Gil at opelgtsource and he ll answer all your questions in 10 min
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    Quote Originally Posted by jthorny1337 View Post
    Hi again. Thank you all for the help and advice.

    I plan on just cruising around and maybe making some weekend runs up to a mountain town. I live in the colorado front range, so torque to get up the mountain roads is more imporant than WOT racing for sure.

    I already have a 38 DGAS and pertronix ignition in the car so I guess I will just go w/ the 2L valves and 2L pistons since I am doing all of this. So far as I know my head is original to the car (1970). I think I will also just go w/ the OGTS 2L pistons since they seem like the easiest path forward and they fit.

    I just have a couple questions..
    • What parts should I order for the head conversion? My machinist told me that my valve stems were tight so would I just need new 2L valves, valve stem seals, and 2L valve seats?
      For the block do I just need 2L pistons and rings? I assume I can use my factory crank and rods?
      I do not know if it has a factory cam in it or not so I will probably just run that for awhile.
    Well that is an interesting tidbit, about where you live. What minimum altitude will you ever drive at? The reason to ask.... at those altitudes, you need all the help you can get to ingest air. Altitude works like a form of turbocharging, except the pressures are negative rather than positive. In that case, I take it back on the valves.... it is going to help, at least a bit.

    It also changes the equation on the pistons. The matter of DCR (dynamic compression ratio) is they key to low RPM torque. When you go up in altitude, the cylinder filling goes down, and DCR drops. So at altitude, you can go with higher static CR to compensate.

    I just ran some numebrs with those Wossner pistons and made some assumptions on parts and such as follow:
    - Head chambers 52 cc
    - Wossner piston domes - valve relief 10.7 cc (from catalog)
    - Piston deck height -.004" (standard specs and this piston)
    - Head gasket thickness .042"
    - Misc volume 1 cc

    Static CR works out to 10.7:1... very close to the Wossner catalog number.

    If you changed cam to the 6059 at OGTS, then dynamic CR (DCR) works out to 8.5 at sea level. That is too high.

    BUT if you rework the effective DCR at 5000', then all of a sudden it is 7.4 to 7.5.... That is a nice number to be at. Pump gas, no problems. And the larger cam wil make those larger valve work well. It will be a whole different engine.

    If this of interest, there is one parameter I want to double check. And if you ever plan to go to lower altitudes or sell the car there, then this is not a great idea. But I wanted to suggest an alternative based on your altitude. Engine building parameters change quite a bit out there.

    And yes on the factory crank and rods on all the options presented, unless there is something different in the pin diameter for the Wossners as suggested.

    Edit to add: As Bob said, the pins are 22mm for the Wossners vs the stock 23 mm. So some bushings in the rods would be needed.
    Last edited by Manta Rallier; 3 Weeks Ago at 05:56 PM.
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    Thank you for that info and for the math! I am not 100% sure what DCR is yet but I will do some reading. I am familiar with static compression ration.

    I will mostly drive the car at about 5000 ft above sea level and I would want to design it with that in mind. Trips up to the mountain towns would take me to 9k ft... but my time there would be really limited in comparison.

    I am going to call OGTS to sort out some costs for the parts shortly.. tomorrow worst case but the piston selection is a huge part of it (and the cost) so I definitely want to get it right and I appreciate all the help I can get.
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    OK, like static CR (SCR), dynamic CR (DCR) is a mathematical computation. SCR represents the compression of the fuel-air mixture as if the intake vale closed exactly at the end of the intake stroke with the piston at BDC (bottom dead center). In reality that does not happen..... the intake valve does not fully close until the piston is partway up on the compression stroke, after BDC. The cylinder does no start building pressure until the intake valve is really closed, and DCR is the way to account for the actual closing point of the intake valve partway up on the compression stroke.

    The ultimate goal is to account for the actual pressure and temperature that the fuel-air mixture experiences before it is fired. The actual pre-firing pressure/temp is a strong indicator of whether the mixture will want to detonate (explode) at some point in the combustion process, or smoothly burn like we want. So the DCR number is an aid to predicting that by accounting for the actual time of the intake valve closing.

    Since what we are dealing with is actual pre-firing pressure/temp of the mixture, if there is less cylinder filling for any reason, that pressure/temp will be lower. Less cylinder filling can be due having the throttle only partially open, or having the outside pressure lower like at high altitudes. So the next improvement in figuring this out is to account for altitude. Once that is done that is often referred to as 'effective CR' or 'effective DCR'.

    So the question them becomes, why don't we just always run a very low SCR and DCR and never worry about detonation? The answer is that we want good torque out of an engine at lower RPM's so we can have an engine with a flexible operating RPM range. The higher you can push the pre-firing temps/pressures, the higher the pressures will be during the combustion process and the more torque we will get out of each cylinder's combustion process. This really shows up big time at the lower RPM's. So if you want want a good wide operating RPM range (important for street driving in general and moreso for manaul trannies), then you push up the effective DCR closer to the optimum without going too far and getting into possible detonation.

    I hope that makes sense.

    Again, optimizing this for high altitudes is do-able but if the engine is taken to sea level....watch out! Time to retard the timing, run high octane, non-pump fuel, enrich the mixtures, and hope it works. So that is one 'word of warning'. The other is that with the Wossner pistons, the cam is increased in size and so the low RPM idle will tend to be rougher, and tuning will typically be more difficult for less experienced folks. It would be worthwhile to ask here what others think of that larger cam.
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    So I unbolted everything from the engine... bell housing, etc. and it is ready to be pulled. I also called OGTS to get some pricing on parts for a build. All that went well, but I was very confused about something I found.

    I am not an expert engine builder by any means, but I have rebuilt a couple 302's in the past. I have never seen or heard of an exhaust manifold like this and I was wondering if any of you had? Is this normal or a normal mod?

    Thanks in advance.
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  18. #16
    1000 Post Club Vincent's Avatar
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    Quote Originally Posted by jthorny1337 View Post

    I am not an expert engine builder by any means, but I have rebuilt a couple 302's in the past. I have never seen or heard of an exhaust manifold like this and I was wondering if any of you had? Is this normal or a normal mod?

    Thanks in advance.
    Looks like a typical generic aftermarket gasket to me. No special mod there. They are designed to accommodate headers as well.....
    Last edited by Vincent; 2 Weeks Ago at 11:14 PM.
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  19. #17
    Mike's Opel Shop Site Supporter opellane's Avatar
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    Quote Originally Posted by jthorny1337 View Post
    So I unbolted everything from the engine... bell housing, etc. and it is ready to be pulled. I also called OGTS to get some pricing on parts for a build. All that went well, but I was very confused about something I found.

    I am not an expert engine builder by any means, but I have rebuilt a couple 302's in the past. I have never seen or heard of an exhaust manifold like this and I was wondering if any of you had? Is this normal or a normal mod?

    Thanks in advance.


    I think your talking...asking about the exhaust manifold, not so much the gasket.

    That's normal, as those two ports are exhaust ports for cylinder #2 and #3
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    Opeler
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    Okay thanks. I was confused why the gasket had a separation between 2/3 and not the manifold. I have never seen exhaust ports combined like that before.
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    Mike's Opel Shop Site Supporter opellane's Avatar
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    Quote Originally Posted by jthorny1337 View Post
    Okay thanks. I was confused why the gasket had a separation between 2/3 and not the manifold. I have never seen exhaust ports combined like that before.
    Here a photo of my broken Sprint Manifold, see the ports are combined mine is cracked
    But I think your using a different exhaust gasket maybe?
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    Josh great timing on your rebuild as I'm going to be rebuilding a 1.9S that I just pulled from a 1970 Opel GT. Its going to be my winter project and you have already helped by greasing the wheel for me. I will be intently following your progress. I may even PM you if okay to inquire further. There is a tone of information on this forum with awesome expert advise.
    Good luck and get your Opel GT back on the road.

    Dan
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