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how much blowby is normal?

Discussion in '"Stock" Alpine' started by mightyohm, Jul 9, 2018.

  1. mightyohm

    mightyohm Donation Time

    We're breaking in the new 1725 (new rings) and chasing various oil leaks. We are running the early style valve cover and open crankcase ventilation from the series II. When I remove the vented oil filler cap and place my hand over the fill tube, I can feel a very noticeable pulsation of air moving through the tube. I'm not seeing significant amounts of smoke or mist coming out. I think I remember the old 1592 being similar. How much is normal?

    As an aside, don't try to use the late style side cover with the short upturned pipe and install a crankcase breather on the pipe. The breather will become saturated with oil and will make a big mess! Lesson learned.
  2. Hillman

    Hillman Gold Level Sponsor

    I suspect a fair bit is ok. My, now dead by fire, SII had a 1725. SII valve cover and open pipe side cover. Compression was 140 (on all cold) and higher and even when hot, burned little oil. Blowby blew the oil filler cap off on a long uphill climb of the rockies in BC.
  3. mightyohm

    mightyohm Donation Time

    That’s good to know. Sorry to hear about the fire. Did you have to modify the side cover so that the draft tube cleared the engine block? My tube runs into the block so I can’t run the draft pipe without modifications. I’m running the later style side cover for now but want to convert to the early draft pipe setup.
  4. Hillman

    Hillman Gold Level Sponsor

    I bought the car with an open pipe on the side. I think it was an early side cover, but it wasn't me who installed the 1725 so I can't say for sure.
  5. Alpine 1789

    Alpine 1789 SAOCA President Diamond Level Sponsor

    I had an idea a while ago to create a device for measuring blowby. A long clear tube that would fit on top of the oil filler with a ping pong ball in it. You'd measure the average height of the ball in the tube and be able to say: "I have 24 inches of blowby". Take it to an event, measure a bunch of cars with different aged engines and quickly have a standard for measuring a healthy or tired engine.

    I have no idea if this would really work or not, but thought I'd toss it out there in case it was worthwhile trying.
  6. Tim R

    Tim R Silver Level Sponsor

    Interesting comments about the vent pipe on the tappet chest side cover. At various times Rootes had a down facing pipe, an up facing pipe and finally did away with the vent pipe completely for later 1725 engines.

    All of the top area of the engine is joined atmospherically through the pushrod channels so Rootes obviously felt that they only needed to have one top end breather which they took from the filler neck, put it through the flame trap and into the air filter. I have often wondered if there are increasing problems with this later set up as the engine wears and blow by, presumably, increases.

    I have seen cars here in the UK running with tappet chest and filler cap breathers joined directly by a short pipe, both fed into a catch tank and various other set ups with the pipes vented into different intakes or out straight to atmosphere. On the three Alpines in our family, all are running different engine vent systems and all work fine.

    The one thing that I know from experience that you have to watch is venting into the new club Weber inlet manifold with a pcv/pcd valve. On Series V cars originally this valve was an early attempt at emissions control and vented into a chamber shared between all 4 cylinders. The new club manifold has a threaded hole in number 4 intake only that was originally intended to have this valve fitted to it. Unfortunately if you vent into there it makes the engine run too lean on number 4 on acceleration. Now the kit is sold with a blanking plug in that hole and members are advised to vent alternatively to atmosphere, to a catch tank or elsewhere.

    Tim R
  7. Eleven

    Eleven Platinum Level Sponsor

    I am now a bit confused. The vent to the intake was intended to suck air through the crankcase so that there is an airflow. (Positive crankcase ventilation or PCV) From what I remember not doing that they found increased wear and such; in other words it was more than just emissions but improved the engine life. Venting to a catch tank or atmosphere would return kill PCV benefits. When we were racing we went to a catch tank; A) it was required and B) we were going to rebuild often anyway. I got my intake for my Weber 32/36 from Rick at Sunbeam Specialties. The PCV screws into that (side gripe, no water jacket so cold running sucks) and have notice that my plugs are not uniform in color; so are more lean than others. I am not sure what a "club" manifold is so that might explain it; what is a "club" manifold? I put down the non uniform coloring to poor intake design with all the right turns. Hmm, I wondered if the additional air from the PCV might have an effect.
  8. alpine_64

    alpine_64 Donation Time

    The club manifold ia the one (webcon ?) in the UK developed with members of the SAOC.

    Its based off the new zealand and italian magnotesi curved runner dgv design as a base.

    A pcv running from a single runner rather than a plenum will impact a single cylinder more
  9. Tim R

    Tim R Silver Level Sponsor


    Here are some pictures of the 'club' manifold, correctly described by Michael above. When they were developing it they studied what happened with the standard single carb four branch 'Log' manifold and found that cylinders 1 and 4 often ran rich as too much fuel collected in these inlets, not vaporising correctly and causing problems. The curved inlets were designed to improve and balance air flow across all four cylinders and coupled with an induction manifold and closing of the horn opening apertures (so that only ambient temperature air is drawn into the carb) there is a very noticeable improvement to performance.
    The one mistake they made when producing this new manifold was in tapping a hole for the PCV in inlet No 4. It causes that one cylinder to run far too lean. The standard treatment in the UK is to fit a metal plug to the tapped hole and get rid of the PCV completely. A rolling road test identified the problem fitting the PCV to No 4 inlet causes in less than a minute !

    Later 1725 engines had no tappet chest breather and many owners have retro fitted the plain unvented side covers (which sell for £16 in UK), I can't see why Rootes would have done away with it if there was any risk of it increasing wear but stranger things have happened!

    The DGV carb and new manifold are available from UK company Alpine Innovations (I have no connection with them but their products are very good and I have purchased two of these manifold and carb sets ups and various other parts from them).

    Tim R

    Sunbeam-Alpine-Inlet-Manifold-1st-Casting-006.jpg Nick's Alpi Carb.jpg
  10. Rootes 66

    Rootes 66 Donation Time

    On later engines they did indeed have a plain tappet chest cover, But they actually increased air movement capability with the larger vent on the oil filler /larger bore on flame trap.
  11. Bill Blue

    Bill Blue Platinum Level Sponsor

    I think all of this means that a lot of blowby is perfectly normal.

  12. 65beam

    65beam Donation Time

    It seems the engines are still like they were when new. As long as they run and gas is $2.52 / gal I don't worry about mileage, blowby or oil leaks.
  13. johnd

    johnd Donation Time

    Having read all of the above, what is the proper way to "plumb" (or plug) the orfices on the (1) oil filler tube, (2) Weber carb, (3) intake manifold (Pierce model) and tappet cover? Is there even a consensus on this?
  14. Tim R

    Tim R Silver Level Sponsor


    I think it is fair to say that there is a lack of consensus on how best to set up engine venting if you move away from the standard set up and Rootes clearly changed their own views on what was best as they changed the 'standard' set up several times over the life of the engine!

    Tim R
  15. Tom H

    Tom H Platinum Level Sponsor

    I am skeptical about late Alpines having plain tappet covers from the factory. I had a pretty late SV, B395016834 LRX, and it had the standard SV PCV set up, as does my present SV, B395013103 LRX . I see no documentation of this change in the "Production Changes" section on this site. Can anyone document this change? The Parts List only lists ONE tappet Cover. Any service bulletin address this? Or is that a change that took place on post-Series V engines?

  16. Rootes 66

    Rootes 66 Donation Time

    Tom The Plain tappet chest covers referred to are on the arrows engines.
  17. Tim R

    Tim R Silver Level Sponsor

    As far as I am aware they were never fitted to Alpines as standard but went on all the later 1725 engines through to the end.

    Tim R
  18. mightyohm

    mightyohm Donation Time

    I measured leakdown this weekend. 200 miles on the motor.
    I measured compression and leakdown with the motor cold. Numbers would probably improve hot but I didn't want to risk stripping a spark plug from a hot head and I figure it's more about the relative numbers anyway.

    Leakdown was 17%, 4%, 9%, 7%.
    Compression 160, 175, 180, 165 psi.

    All of the leakage is past the rings, I can hear it in the crankcase.
  19. husky drvr

    husky drvr Platinum Level Sponsor


    Just a quick thought - when you installed the piston assemblies, is it possible you allowed the ring gaps to line up instead of being staggered across the piston? If the gaps line up, then the pressure would have a much easier escape path - as compared to the labyrinth if the gaps are staggered.
  20. mightyohm

    mightyohm Donation Time

    I staggered the rings per the manufacturer's instructions. The rings are free to rotate, however. There's nothing to keep the rings from rotating and lining up after installation. I don't think that alignment of the ring gaps would affect a leakdown test because the leakdown test uses a slow, constant flow of air vs. a sudden combustion event.

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