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| Can anybody heartily recommend a company for a rebuilt short block? https://slantsix.org/forum/viewtopic.php?t=63378 |
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| Author: | Doctor Dodge [ Thu Mar 14, 2019 5:08 pm ] |
| Post subject: | Re: Can anybody heartily recommend a company for a rebuilt short block? |
An effective compression ratio calculator (using actual measurements) is your friend. https://uempistons.com/p-27-compression ... lator.html Set the effective compression to 8 to 1 and you will have a 'spunky' engine the runs on pump gas. Guessing or "wishful thinking" will get you... ??? ... less then optimal performance. DD |
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| Author: | and739 [ Fri Mar 15, 2019 6:31 am ] |
| Post subject: | Re: Can anybody heartily recommend a company for a rebuilt short block? |
Thanks for posting the link Doc. This is very helpful. Other calculators I have found ask for an SCR to be input. I'm understanding now that SCR is the end point, not the beginning. This calculator makes that apparent. The calculator asks for: Intake Closing Point (degrees) ABDC @ 0.050 lift plus 15 degrees. Is this 15 degrees true for all camshafts, or is this a rule of thumb to cover most cams? I assume this addition is done to get close to 0.000 lift where the intake valve is completely closed, correct? |
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| Author: | Daddiojoe [ Tue Mar 19, 2019 3:31 pm ] |
| Post subject: | Re: Can anybody heartily recommend a company for a rebuilt short block? |
Good news! Rick called it--broken head gasket between two and three. I ordered some ARP head bolts (they wouldn't give me an AARP discount, though) in hopes that new bolts will keep that from happening again. The old bolts were indeed pretty old. Thanks for your help, everybody. I will let you know when it's running again. Joe |
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| Author: | DadTruck [ Tue Mar 19, 2019 6:59 pm ] |
| Post subject: | Re: Can anybody heartily recommend a company for a rebuilt short block? |
If you blew a head gasket with in 2000 miles of a rebuild, I would place the fault with either: 1) improper torque applied to the head bolts Or 2) bad surface finish or profile on the block or head. You will be able to inspect for issues with the surfaces, Remember too smooth can be as bad as too rough for block and head decks. If nothing suspect is found on the surfaces, torque or torque sequence is the likly cause. Bad torque can be caused by: Wrong specification used Operator error Torque wrench out of calibration Bolts not lubed or dirty or bad threads Threaded holes in block dirty or defective Regardless, I would be in serious discussions with the shop that built the motor. Slants with near stock compression should not have head gasket issues. The shop that built the motor screwed something up. The blown head gasket is your proof. They owe you. |
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| Author: | Doctor Dodge [ Wed Mar 20, 2019 7:58 am ] |
| Post subject: | Re: Can anybody heartily recommend a company for a rebuilt short block? |
Was the block's deck resurfaced by the shop? If so, how much material was removed? If the block deck was not resurfaced then pull out the dowel pins and lightly sand the deck with a sanding block to help highlight high and low spots. The photo below shows how bad the flatness on the deck can be with the shinny "stripes" being high spots on this block's top deck. DD 
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| Author: | Daddiojoe [ Wed Mar 20, 2019 9:56 am ] |
| Post subject: | Re: Can anybody heartily recommend a company for a rebuilt short block? |
Thanks for the tips, especially on sanding the head. I neglected to mention that the head had been rebuilt years ago and enough ground off to give me a 9.5:1 compression ratio. Should I use a different than stock head gasket? Joe |
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| Author: | SpaceFrank [ Wed Mar 20, 2019 11:13 am ] |
| Post subject: | Re: Can anybody heartily recommend a company for a rebuilt short block? |
Okay, the compression ratio being raised is important info. Do you know what your initial ignition timing and total mechanical advance is? Are you running regular pump gas? Also, what kind of cam are you running? You need that info to determine your dynamic compression ratio (DCR), which is more relevant for this question than your static compression ratio (SCR). If your total timing (initial + mechanical) is much over 30°, you may have issues running pump gas at that compression level. Trust me, I have a stack of burned head gaskets hanging on the wall of my garage from learning this lesson the hard way. ARP head studs are nice, but they won't help if you're killing head gaskets from pre-ignition. |
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| Author: | Daddiojoe [ Wed Mar 20, 2019 7:43 pm ] |
| Post subject: | Re: Can anybody heartily recommend a company for a rebuilt short block? |
Frank-- I am running propane, which has over 110 octane. I don't remember what the timing is currently set at--10 degrees before TDC sounds right, and I haven't done anything fancy with my Mopar electronic ignition's springs or weights. I am running the Erson RV cam that was offered to Slant Six.Org members at a discount many years ago. I really don't know about DCR. I should look that up. With the above information, do you think I need some type of special head gasket? Thanks for the reminders. |
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| Author: | SpaceFrank [ Wed Mar 20, 2019 9:11 pm ] |
| Post subject: | Re: Can anybody heartily recommend a company for a rebuilt short block? |
Oh, ok. I don't know anything about propane; maybe some other folks here can chime in on that. They might also know something about the cam you mentioned and the mechanical advance you probably have if your distributor is still stock (I assume a 1971 D-100 from your signature). At 9.5 SCR, you shouldn't need a special head gasket or ARP studs. I'm just worried about your ignition timing, but with propane I'm not sure if that's such a big deal. Like others have mentioned, it could also be a machining or assembly issue. There's more than one way to blow a head gasket. |
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| Author: | Doctor Dodge [ Thu Mar 21, 2019 10:52 am ] |
| Post subject: | Re: Can anybody heartily recommend a company for a rebuilt short block? |
Quote: ...
Correct. Finding the actual intake valve closing point (IC) is the key here and that +15 degrees at .050 lift is a "band-aid" way to get close, especially with hydraulic cams.The calculator asks for: Intake Closing Point (degrees) ABDC @ 0.050 lift plus 15 degrees. Is this 15 degrees true for all camshafts, or is this a rule of thumb to cover most cams? I assume this addition is done to get close to 0.000 lift where the intake valve is completely closed, correct? Me, I mock-up the engine, set the actual valve lash I will be running and find the IC with that setting, then use that number in the calculator. Basically, I go and find what the engine will actually "see" and do my calculations with that (those) numbers. I also try some different lash settings during the process, especially focused on where the end of the lash ramps are so the effective compression (EC) supports different lash settings. This helps to "fine-tune" the running engine. (loosen the lash and EC goes up, tighten the lash and it goes down slightly) DD |
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