Steel shim gasket coolant hole issues. 70 455 with 67 big port heads.

Discussion in 'Street/strip 400/430/455' started by Don's70GS, Jun 25, 2018.

  1. Don's70GS

    Don's70GS Member

    Rebuilding a 70 455 using 67 big port heads (1382983). An NOS 1970 455 GM steel shim gasket is being used. There is a slight difference in cooling passages in 70 block vs 67 heads. But, this is not the issue.

    On the 70 455 block there are: 2 top passages (r & l ends); and 3 bottom passages. Plus "slots" r & l.
    On the 67 heads there are: 3 top passages (r, ctr, l); and 3 bottom passages. Plus "slots" r & l.


    The GM 1236030 steel shim gasket (1970 455) does not provide a passage for the (non-existent) center coolant passage in the 70 455 block. The top center hole in the 67 head is simply blocked off by the steel shim gasket. The surplus coolant passage in the 67 head is simply not used. Cooling wouldn't seem to be a problem because of 1 un-used coolant hole.

    However steel shim gasket 1236030 has two other coolant related issues:

    1) the 1236030 does not provide drilled holes for the bottom 3 coolant holes. These holes are blocked because the steel shim gasket is not drilled at these 3 points. Thus coolant flows from block to head only thru the top 2 holes at r and l(and the slots on the ends). It does not make sense to not use the bottom 3 coolant holes.
    Wouldn't engine cooling benefit if the bottom 3 coolant hole were drilled in the steel shim gasket?

    2) the pre-punched coolant holes in 1236030 are very small at 3/16", compared to the 1/2" holes in the block & heads. Would coolant flow improve with enlarged holes, or would this upset the engineering design for flow and pressure?
     
  2. Mark Demko

    Mark Demko Well-Known Member

    Never alter the coolant holes in gaskets.
    Some smaller holes are "steam" holes
     
  3. Don's70GS

    Don's70GS Member

    Thanks Mark, your advice makes sense. Don't mess with the factory design (for head gaskets anyway). However, my gasket coolant hole puzzle has deepened slightly today.

    I have two sets of NOS 1236030 steel shim head gaskets( 1 set McCord & 1 set GM). This morning I did a side by side comparo and found the McCord 1236030 has 3 coolant holes across the bottom, and the GM 1236030 (unopened package) set does not have these 3 punched coolant holes in the bottom. The McCord set was purchase from Gessler's. They were installed 600 miles ago,and just came off the engine. The McCord set is embossed with both GM and McCord numbers and has never been altered.

    The 455 ran warm at 190, so I'm concerned about going to the set without the 3 coolant holes across the bottom.
    end of reply, Don
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

  5. Don's70GS

    Don's70GS Member

    Larry,

    Before I posted I did a search on this forum and did not turn up much. Perhaps used the wrong key words in my search.

    Anyway, thanks much for the list, I will take a look at each thread.

    My concern now is the difference between my two sets of NOS 1236030 GM gaskets. Presumably identical, yet one set does not have 3 punched coolant holes at the bottom of head.

    Thanks for the info. Don
     
  6. Don's70GS

    Don's70GS Member

    Larry, (continued)

    I studied each of the threads you referenced. Thanks again. They all answer my main question, and confirm your advice regarding coolant flow(or blocking) and gasket hole sizing/blocking. "Its by design"

    However, my other concern regarding two identical sets of GM NOS 123630 steel shim gaskets having different holes has not been answered. (one set has 3 bottom coolant holes, the other set is blanked at these holes).

    Post 2564206 indirectly mentioned this 3 hole issue as a difference between his 400 block factory steel shim(which had 3 bottom holes) and Felpro gasket (which did not have 3 bottom holes). After discussion of sizing "by design", he was advised to go with the Felpro gasket. The 3 hole difference between the factory gasket and felpro was not addressed.

    So, I'm still puzzled: Why are my two, presumably identical, GM NOS 1236030 steel shim gasket sets different? More importantly, for those who are expert in engine/head coolant flow .....which set should I use in my 455 block/67 head combo? With 3 bottom coolant holes or without?

    Appreciate any further comments on this. Don



     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    From what I can see coolant is pumped into the block, enters the heads at the rear, and then is pumped forwards in the head to the intake and through the thermostat. I don’t think those holes do much of anything. They might hurt flow being open. I’ll wait for others to comment.
     
  8. Bens99gtp

    Bens99gtp Well-Known Member

    I can't directly answer your question, but bbb are not the only motor's to do things like this. Some BBC are the same way........some are series flow, some are parallel flow. Which is better, why when used, I can't answer.

    One thing I do know for certain same part number does not allows mean exact same parts.

    Post some pics of the 2 gaskets so we can see visually the differences if you have the extra time
     
  9. Don's70GS

    Don's70GS Member

    455headgaskets.jpg
    Ok, here is photo of NOS steel shim gaskets, both embossed GM 1236030, and packaged in GM label plastic bags.

    Yellow arrows point out the issue. Three bottom coolant holes in one set, while the other set (in factory plastic) does not have the 3 bottom holes punched.

    I have no real knowledge of the coolant flow engineering for the 455 block/heads. These 3 holes are positioned on the lower side/outside of the block and seem to provide coolant access around the cylinders. Is the coolant flowing up to head thru these holes, or is it possible coolant flows from head down. Should flow at these holes be allowed or blocked? Does it matter either way? I'm going crazy.

    The bottom set, with holes, was on my recently rebuilt 455, and seemed to run slightly hot. Thinking about this, I'm inclined to agree with Larry's comment above. Use the gasket without holes so as to block coolant which is believed flow from back of engine to front(thru the head-end coolant slots). If Larry's guess is correct, use of the 3 bottom holes may have an adverse flow effect.

    Then again, why are the 3 matching coolant holes in the block and head. These holes are well shaped (for coolant?) unlike the odd shaped holes at the corners of the block which are apparently used to empty sand from the casting at the foundry (these block holes are sealed closed by the gasket). Like I said I'm going crazy.

    Thanks for input, and any other comments will be appreciated. Don
     

    Attached Files:

  10. Don's70GS

    Don's70GS Member

    One final comment on this 3 bottom hole issue.

    I just looked at the info at TSP regarding JWs 470ci shortblock. Picture shows felpro style gasket. There are 2 coolant holes at top and 3 coolant holes at bottom. I have the impression that JW does not make mistakes. Certainly good enough example for me to follow

    Looks like gasket I use is the one with 3 punched holes on bottom.

    Thanks again to all who offered comments on my gasket issue. Don

     
  11. Bens99gtp

    Bens99gtp Well-Known Member

    I think even though they carry the same part number, clearly the gasket flow different. The one with the bigger 3 holes in the bottom looks to be more a parallel flow setup allowing coolant to more evenly flow up around all the cylinders and head area closet to the same. The one without looks more series were the water flows more from the front of the motor to the rear up into the head then back to the front. This will leave the front head area hotter than the rear and the front cylinders cooler than than the rear. Uneven cooling
     
  12. Don's70GS

    Don's70GS Member

    Ben, Thanks for the input.

    Who knows why the 2 sets are different, but I'm guessing you are correct that the bottom 3 holes should be used and will improve cooling.

    Don
     
  13. Buicknutty

    Buicknutty Member

    Gents;
    I've done some searching here, but really haven't found any answers. I have a stock and very original '69 Electra with a rebuilt 430 which has overheating issues. By that I mean at 65-70 MPH it will start to run at 220+, then when I slow down it cools off. This is when ambient temps are reasonable.
    I'm now running a 160 stat and new four core rad, and though it takes longer to heat up, it still does to about the same extent.
    One of the original heads had a crack in it so on advice I got a set of '71 455 heads as these are supposed to be stronger. I had the engine completely put together by an engine builder with a very good local reputation and he has done BBB's before.
    The oiling system was improved, cam upgraded to Stage 1, with larger valves to match.
    From the get go it would run hot at highway speeds, at first it was believed the engine was tight, but it is still an issue with over 5,000 miles on it.
    All of the "usual" stuff has been checked and double checked, timing, hoses, etc. etc.
    Recently we took it on a tour on a warm late afternoon, early evening summer drive. The leader didn't take us over 45 MPH, speeds were kept 40-45, and it ran at 165 the whole time. Then on the way home I ran it at 55-60, and then it ran about 195 or so. I'm sure if I'd upped my speed to 70 or so it would have gone well over 200.
    On this site and another source I found, saying that there are cooling passages which need to be blocked to use the early 455 heads on a 430. If this wasn't done, would this explain my problem?
    Then if so, would taking the heads off and blocking the passages cure my problem?

    Otherwise the car is fabulous, runs strong and is a great driver, but this issue limits me.

    At this point we are convinced there must be something amiss inside, but I don't want to tear it down without knowing what to look for.
    Thank you.
    Keith
     
  14. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Vacuum advance working? Is your timing at or above 40* at cruise RPM?
     
    bostoncat68 likes this.
  15. Schurkey

    Schurkey Silver Level contributor

    Does the timing mark on the damper align with "zero" on the indicator, when the #1 piston is at TRUE TDC?

    The "rule of thumb" for overheating is "too hot at idle or low speed is lack of air flow. Too hot at highway speed is lack of water flow." I have not found that to be entirely true. But it's a start.

    Eroded water pump impeller? Cheap water pump? Water pump clearances not correct? Incorrect pulley ratio between crank pulley and water pump pulley?

    Overly-lean fuel curve at higher speed, due to plugged carb passages, oversized air bleeds, mis-matched carburetor castings, low float level, vacuum leaks, weak fuel pump?

    Lack of air flow due to folded or dirty fins on the A/C condenser?

    Missing rubber seal at rear of hood, by windshield? Any air that comes into the engine compartment from the high-pressure area at the base of the hood, interferes with air coming in through the radiator. That's why there's a seal there to begin with; and why every OEM "cowl induction" hood is sealed to the air cleaner instead of bleeding air into the engine compartment. The faster you go, the more important that seal is.

    Once you figure out the REAL problem(s), scrap the 160 thermostat. 180--195 is more reasonable.
     
    Last edited: Jul 2, 2022
  16. Buicknutty

    Buicknutty Member

    Ok, thanks for the responses, to answer a few questions, I just double checked and the new vacuum advance from 2 years ago isn't working. The rad is new and clean, and while it was out I made sure the condensor was clear as well.
    The water pump is new, and is a stock unit. I do have a high efficiency one from TA, but swapped back to a new stock one in case that was an issue.
    All the pulleys are correct, to the best of my knowledge. However the timing chain cover is new, as the original one was corroded somewhat though the more extreme cooling issue started after the rebuild. But I do wonder if there is an excessive clearance in the water pump cavity.
    I drained the rad a bit and looked and I could see there was coolant flowing through the tubes into the tank. Whether is not it's sufficient that don't know, but there is a decent flow.
    I have wondered if at higher speed there is a lean condition, and excaberated by the slightly hotter cam, The original Q jet is rebuilt too.
    Keith
     
  17. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The vacuum advance will advance the timing on the highway 14-18*, and that will make it run cooler on the highway all by itself.
     
  18. Buicknutty

    Buicknutty Member

    Thanks, but getting back to my original question, I recently read when putting 455 heads on a 430 certain cooling passages need to be blocked to allow for proper coolant flow.
    The vacuum advance failure is a recent development, which I'll have repaired shortly. It does have advance, it is not retarded, though a proper advance will improve response too.
    A bit of hesitation off of the line is what has lead me to find a advance not working.
    Does anyone have experience with this head swap, and is it correct? I had believed they could be changed and will work well as long as the related valve train parts are upgraded.
    Sorry too, I should have put this in a different thread rather than piggy backing on this older one.
    Thanks again.
     
  19. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    If the heads and block were incompatible, the engine would have a giant coolant leak into the valley.

    CylinderHeadScallops.jpg
    Without the vacuum advance, the engine will run relatively retarded and it will run hot. It's a really simple thing to put a timing light on it, rev the engine to cruise RPM, and measure the ACTUAL ignition timing at that RPM. It should be close 40* or so. Can you do that and come up with a number?
     
  20. DaWildcat

    DaWildcat Platinum Level Contributor

    Mart likes this.

Share This Page