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Building a 1725

Discussion in '"Stock" Alpine' started by Jim E, Jan 29, 2007.

  1. Jim E

    Jim E Donation Time

    Bob B. has ask me to build a 1725 for him to replace his 1600 that busted the crank. This is for his SIV.

    I have the 1725 out of my S3 that is a fresh build but the block is cracked in the outside water jacket. First I was going to have the crack welded up being a couple guys I know said they could do it... well one finally said nope and the other just never did it.

    There was one option which is to stitch weld the crack, this involves drilling and tapping the crack with a special tappered bit and tap then screwing in these tappered bolt looking gizmos and breaking them off, grind smooth and repeat until the whole crack is done. I have seen this done on other engines and it works but the cost of the plugs and the installation is so high it makes more sense to just get a new block, being the crack in my 1725 is over a foot long.

    So Bob found a 1725 bare block and we meet up this weekend and I got the block from him, and we talked about the build. Looks like a mild port on the head, lighten up the flywheel, KB grind cam from Delta and I will clean up the casting flash and such on the oil returns for the block and head. So more or less just a basic rebuild with a few small upgrades. That is unless he decides to go chevy rod....


    Here is Bob's block in my pickup... now off to the machine shop to see if it will clean up at 30 over and have it checked for cracks...
  2. Bill Blue

    Bill Blue Platinum Level Sponsor

    "That is unless he decides to go chevy rod...."

    What's to decide? There are so many up positives to this conversion, longer stoke, lighter, stronger rods, more piston/ring choices, what are the negatives?

  3. RootesRacer

    RootesRacer Donation Time

    Small crank journals (you go from 2.125 to 2.000 to use STD SBC bearings).

    Welding the side of the rod BE (in the case of stock V8 rods).
    Using the 6 cyl rods and machining them to alpine BE width dimensions.
    Having the crank journals widened to accommodate the larger 6 cyl rod BE width.

    The cranks are made of iron (not steel), so cutting down to chevy journals weakens the rigidity of the crank. Widening the journals cant help with strength either.

    The piston/rings/pins only opens up if you go custom pistons, it is otherwise possible to re-bush the rod little ends to take the larger and heavier rootes pins.
  4. Jim E

    Jim E Donation Time

    Block is in the hot tank, could be bored this after noon if it is a good one.

    I really don't think there is enough meat in the small end of the Chevy rod to put a bushing in it. I have honed them to float the Rootes pin with no bushing.

    Pretty sure this one will be a stock rod engine.
  5. Bill Blue

    Bill Blue Platinum Level Sponsor

    Jarrid, I suppose the question is: Are the smaller rod journals a problem? The cranks are not known for being weak and the lower reciprocating mass (maybe 8 ounces?) should 'take a load off' the crank, especially near red line.

    I seem to remember someone identified an OEM GM piston that would work with the chevy rod, was about the equivelant of a +40 Alpine. Checked the old forum, the search function still SUCKS.

    Why would a heavier Alpine piston pin be an advantage?

  6. V6 JOSE

    V6 JOSE Donation Time

    I would go with the Chevy Six cilinder rod, but have it ground to the Alpine 1725 rod width. Any of the other options will be costly, and will not help the longivity of the crank. Turning the rod journals undersize, won't weaken the crank. Unless you plan on turbocharging, supercharging, or nitrous oxide will be used. Even with the power adders, I would still think it would be alright, but who knows for sure. The lower surface speed of the rod bearings will lower the heat generated there, thus lowering the stress. The lighter Chevy rods and aftermarket pistons, will also lessen the stress the crank will see.

    I used to own a crank grinding shop, and have done this procedure on many other make cranks, with no problems. These stroked cranks are raced regularly, yet perform well. I think the Chevy rod mod for the Alpine four cylinder is probably the best thing you could do to make it last. If I were to build an Alpine 1725, it is the way I would choose.

    Jose :)
  7. RootesRacer

    RootesRacer Donation Time

    You asked the disadvantages, there they are.

    I myself have built 2 chebby rod motors, so obviously I am not against it.
    I spent a great deal of money on mine, so I feel the the downsides are not as likely to manifest themselves in my own case.

    My additions to the chebby rod formula are high quality crower rods, which are what you would put in a 600hp chebby V8, good for 8000+ RPM.
    I also had the rods, crank and everything else that rotates spun and balanced as a set.

    On the piston, no the alpine bore is too small for any common piston to fit.
    No SBC piston is even close in the bore dept.
    Considering what a set of OEM pistons fetch, seems to make sense to spend perhaps 40% more for a set of forged pistons, which are considerably lighter than the cast stock ones.

    And lastly, there is no advantage in the heavier rootes pins. They just happen to be the ones that fit the stock pistons.
    I used lightweight SBC pins, which are made for teflon pin buttons, which eliminates the circlip rings, and allows the pins to be much shorter, which saves even more weight.
  8. jumpinjan

    jumpinjan Donation Time

    Yes, they are not weak. I have seen a few Alpine engines with spun rods and they never broke (rods or crankshaft). I do have a 1725 oil pan with some puncture in the side of the oil pan, probably a thrown rod. I know the series 1 rods are weak and they will break.
    But for the 1600/1725 cranks to break, it has to flex laterally or torsionally or sheared by centrifugal forces at very high RPM. These engine don't put out the power for these forces to be much of a concern. A 2" diameter crankpin, used in the 1600 & Chevy rod conversion, is not stressing the reliability of the engine at all. I like the Chevy rod conversion because I save the old 1725 crankshafts (that I couldn't use in a rebuild because they were reground in error) and the better bearing material from the Chevy Clevite bearing shells;)
  9. Bill Blue

    Bill Blue Platinum Level Sponsor

    Jarrid, the piston I am referring to is not a SBC, but some other GM that uses the same piston pin diameter. However, can't find the post. Maybe its just a vivid dream.

  10. Jim E

    Jim E Donation Time

    I shopped around a LOT for an off the shelf piston and I can say with some confidence there is not one.

    Bob's blocked magnifluxed good and is rough bored. Now I will take a grinder to it and remove the casting flash from the inside. I think this is important being on this block I could break a piece of flash off with my finger.

    Next up.... the oil galley plugs come out and the freeze plugs, then it gets a final hone of the bores to the pistons, decked and hot tanked again.

    We then look at the crank and see if it can get by with a polish or if it needs turned, then balance the rotating assembly.

    Cam, lifters and rockers needs to head to Delta... and once I know where we are on the crank bearings and rings will be ordered.
  11. Jim E

    Jim E Donation Time

    Here is a picture of the block as I picked it up from the machine shop. You can see the hot tank took off most of the grease and grime but none of the rust. Also if you look close you can see traces of the yellow dust used when you magnaflux the block for cracks. We really checked this one out pretty much all over including the deck. Do not want to build a cracked block.
  12. lemansvk

    lemansvk Donation Time

    JP Pistons in South Australia list them as being available. Here is their website. http://www.jp.com.au/JPPistons.html Of course I can't guarantee they have them, but they certainly had 1592 ones about 5 years ago when my engine was last rebuilt. It might be worth an email

    Cheers, Vic
  13. alpine_64

    alpine_64 Donation Time

    Vic, they are talking modern pistons and rods, not stock stuff. JP will have in stock., but they mostly do flat tops from alpines anyway.
  14. Jim E

    Jim E Donation Time

    Yeah we are talking about using a piston rod combo out of a different engine that will work in the Alpine block. Just is not something that is an easy cross...

    Ok today I pulled the rotating assembly out of my cracked block 1725 and it looks great the crank is 20/20 and all the bearings look great. More or less this is all new bits in a busted block so putting them in the good block should be no problem.

    The "new" block got the freeze out plugs pulled today and being it had never been over hauled before I found just what I figured to find... the back water passage was chock a block full of casting sand from the factroy. Now bear in mind this block had been in the hot tank already but the freeze plugs were in it, so the lesson here is pull the freeze plugs and jab at the junk in the water passaeges with a wire or some such. The clogged passages would certainly cause issues with even cooling or over heating.

    The other thing I did was remove all the casting flash I could get at, the worst place for this was the cam journals. In this area I found flash that you could break off with your finger. So being you cannot get a grinder in this area I used a brass drift and knocked off all the casting flash I could. Then I used a dye grinder and hit all the casting flash I could get at with it and sharp edges. The reason being, at least in my mind for this step is if these small metal bit can be broke with my finger what happens if they let go on there own and get on the rotating assembly.... bad things is what I think.

    Then after all the removing of casting flash and jabbing the water passages I blew the block off with compressed air and you would be amazed at the amount of casting sand that came out if it.

    This block has seen some weathering by the amount of rust on it so I took a wire wheel to it and knocked off most of the rust. Mostly this is cosmetic so the paint will stick better. I am sure Bob wants a pretty engine and the few minutes this took is worth the effort IMO.


    So now back to the machine shop we go to see if the mains are ok and then a final hone, install cam bearings, balance the rotating assembly, lighten the fly wheel and all the other bits that make for a nice mover....
  15. 64beam

    64beam Donation Time

    Hi Jim,

    Thanks for posting this thread. I find it very interesting going through the process of an engine rebuild. Will you install flat top pistons, or are they more for a performance rebuild? Keep the posts coming with the updated pictures.

    Regards, Robin.
  16. Bill Blue

    Bill Blue Platinum Level Sponsor

    Once more, a reference to the casting sand buildup. I have to wonder, is this really sand or aluminum oxide? As the head seems to disappear over the years, the aluminum has to go somewhere.

  17. Jim E

    Jim E Donation Time

    I cannot say for sure what the material is looks like mud or sand could be something else I supose but it was clogged up around the rear freeze plug. Basically I do not think it matters what it is just that it is there and there in lots of engines and needs to be removed whether it is casting sand or...

    Somethig really unusal happened in South Carolina today... it snowed. We were in terror for about two hours then it went away.. man am I glad winter is here and gone.

    The block went back to the machine shop today along with the rotating assembly. the mains were checked and found to be in spec and the crank was pretty good too and may clean up with a polish. So the bores got honed to the pistons and the rotating assembly will be balnced tomorrrow, heck it might have been done this afternoon.

    Then later I went buy another machine shop and was talking about the light weight Isky lifters that are out of production and one thing lead to another and the next hing I know we had the lifters chucked up in the lath and persto change o.....

    Just need to send them off with the cam and rocker assembly for a rebuild, get the new bearings and rings in, port the head and assemble the whole mess and we are done...

    Oh and I got a line on a set of Isky push rods... Bob you want them? say something quick before the thing is done.
  18. Jim E

    Jim E Donation Time

    Thanks Robin. This is going to be a pretty good motor on something of a budget. I am using all but new bits out of the engine from my S3 that has a cracked block. So the pistons are dished and I am going to go easy on the combustion chamber work to keep the compression up there a bit. One thing we have to deal with in the US is crap gas so you cannot go big on the compression. Flat tops puts it up there but with a full on Vizard head it will work but with a standard head you would be pinging. I am fairly certain Bob is going to be surprised with this engine... for a stock rod motor it will be a very nice mover and you can believe that.
  19. Alpine Bob

    Alpine Bob Donation Time

    Jim,What will the Isky push rod benefit the engine? Would it be a stronger? Last longer? Or just better all around engine. Are they stronger than stock? I will be picking up all the things you needed from my old engine this afternoon and can deliver them sometime tomorrow or Sunday if I can get back before the game is over.:) Give me a call on my cell when you get a chance today.
  20. Jim E

    Jim E Donation Time

    They are lighter some say stronger some not, is candy mostly.

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