All Small Six Big external coolant leak on new head gasket

This relates to all small sixes
M

mad_science

Well-known member
Fired my "race" 250 for the first time last night, everything seems good, but noticed a pretty big external coolant leak all down the driver's side of the head/block interface.

Backed off all the bolts and re-torqued, but still leaked.

After pulling the head, can see evidence that all of the coolant passthroughs were leaking between the head and gasket.

Anyone have anything like this before?

I've done ~10 HGs on 250s at this point (courtesy of overheating at the track) and have never seen this before.

Background info:
  • ARP head studs, torqued to 80+ lbs in the proper sequence
  • FelPro gasket, installed without any sealant or goop or anything
  • Head was level-decked at machine shop, not milled down
  • Block was not decked, but checks out as level on machinist straight edge
  • Running 255 pistons, so static CR in the mid-9s
Block and head still look flat on the straight edge.

Don't have time before the race (Oct 1) to send any parts for machining, so at this point our next step is to clean up both surfaces as much as possible and just re-do it. Will probably do a very slight edge break on the edge of the head and block, just to make sure there isn't a knick or high spot that was screwing things up.

If that doesn't work, will probably default to one of the "head gasket in a can" desperation options. If that doesn't work, I've got an $80 Craigslist motor in the back of the garage that might get called in a-la Rudy.
 
mad_science said:
Fired my "race" 250 for the first time last night, everything seems good, but noticed a pretty big external coolant leak all down the driver's side of the head/block interface.

Backed off all the bolts and re-torqued, but still leaked.

After pulling the head, can see evidence that all of the coolant passthroughs were leaking between the head and gasket.

Anyone have anything like this before?

I've done ~10 HGs on 250s at this point (courtesy of overheating at the track) and have never seen this before.

Background info:
  • ARP head studs, torqued to 80+ lbs in the proper sequence
  • FelPro gasket, installed without any sealant or goop or anything
  • Head was level-decked at machine shop, not milled down
  • Block was not decked, but checks out as level on machinist straight edge
  • Running 255 pistons, so static CR in the mid-9s
Block and head still look flat on the straight edge.

Don't have time before the race (Oct 1) to send any parts for machining, so at this point our next step is to clean up both surfaces as much as possible and just re-do it. Will probably do a very slight edge break on the edge of the head and block, just to make sure there isn't a knick or high spot that was screwing things up.

If that doesn't work, will probably default to one of the "head gasket in a can" desperation options. If that doesn't work, I've got an $80 Craigslist motor in the back of the garage that might get called in a-la Rudy.
Click to expand...
How flat with straight edge on deck and head? I know a feeler gauge will slip through somewhere
 
I am wondering if you have enough thread area on the studs so they will pull down to get the full Head Gasket Crush when at the recommended stud Torque, wish I could see it. Good luck
 
The black staining around #6 here shows what we got. The close up shows the machined finish the head has. It's kinda coarse, compared to others I've run...?
20220921_183922.jpg20220921_184026.jpg20220921_184037.jpg20220921_184034.jpg20220921_184007.jpg20220921_183936.jpg
 
Well it doesn't look like the Head Gasket is sealing very well at all, there is no signs of it even clamping down good and most especially on that Push Rod side of the engine. The Head surface finish like that should be fine if its flat. Do you have a good Caliper or a Mic so you can measure the Head Gaskets Thickness in several different areas?
 
OK weird thought, after all the milling are the head bolts too long and are bottoming out before proper clamping occurs??
Maybe add some hardened washers
 
bubba22349 said:
Well it doesn't look like the Head Gasket is sealing very well at all, there is no signs of it even clamping down good and most especially on that Push Rod side of the engine.
Click to expand...
Agreed...the symptoms match grossly under-torquing it, but if anything we over torqued it the first time at 85-90ftlbs (my digital torque wrench records what the final torque applied was). We didn't see any obvious smoking gun that would've propped it up as we disassembled

wme013 said:
OK weird thought, after all the milling are the head bolts too long and are bottoming out before proper clamping occurs??
Maybe add some hardened washers
Click to expand...
We didn't mill any real thickness off the head, just enough to level it. I checked the length of the threads on the head studs and the nuts clamp well before the bottom of the threads.

So, here's the update from tonight:
We decided to go very on brand for Lemons and/or Mad_Science: I bought a $20 glass table off CL, and we glued sandpaper to it and planed the head.

If there was some high spot or warpage, it would show up (or get flattened) as we did that, and if the coarse finish was a problem it would smooth that out.

I gotta admit it felt pretty perverted to do this:20220921_210717.jpg

But in the end it seemed to accomplish something, as some spots were preferentially affected: the outside edges, right around each combustion chamber and in general it knocked down the high spots of the machined finish.

(They're high res pics, so zoom way in)

20220921_222517.jpg
20220921_222436.jpg
We slapped that in with a new FelPro gasket, no copper sealant and torqued to between 77 and 80lbft.

As a sanity check, I double checked my "good" digital torque wrench against a couple of older ones, seems like they all agree we're in the same ballpark.

Tune in tomorrow night to find out if it seals or if I'm going to be asking for recommendations for the best head gasket sealer in a bottle (Bars Vs Blue Devil Vs K-seal)

(As an aside the "we" is me and a couple race teammates; I'm not royalty or anything :p )
 
I had the same issue a few years ago, but not very severe. The driver's side of the head at the block would "sweat", always looked wet. Someone on this forum suggested using the GM Coolant Sealing Tablets that were used at the factory in every vehicle on the assembly line. I dissolved two or 3 in some distilled water and poured into the radiator. The tabs seemed to make the sweating go away, and I am not seeing it anymore.
 
'keeping an eye on this thread - can't figger' if both surfaces are flat and you aren't running out of threads on studs and the gasket is viable - WTF ?

KISS' - (Keep it simple st...) improbables :

> bad one-off head gasket

> are the washers used on head studs or type lube used screwing up torque readings?

> previous damage maybe overheat warping coolant passage area?



'good luck

i do use copper spray typically though should not be necessary with composite . My '63 / 170 has later milled head (48cc's) with steel shim gasket with no leaking for over 10 years.
 
powerband said:
'keeping an eye on this thread - can't figger' if both surfaces are flat and you aren't running out of threads on studs and the gasket is viable - WTF ?
Click to expand...

Yeah, basically.

Searching around online, there are similar stories to mine: "brand new HG with external coolant leak". Under-torqueing is the most common known explanation, but then a few just redid it with a new gasket and now it's fine.
 
bubba22349 said:
The head surface looks so much better with the Glass Table Plaining Job, you can't much flatter than using a good thick glass to fine tune it.
Click to expand...
But glass is flexible. It has to have a good base. The sand paper pictures are also suspect, but if it works it works. A roll of sand paper flattened out would be ideal.
 
I had a piece of polished 1/2" glass AND a Triumph motor cycle. The bike leaked oil. So I dismantled the engine and used 1000 grit wet and dry.
Spent a day lapping the cases, put it back together and it still leaked. The stupid crankcase casting was porous. Never had to lap a Honda.
If done right glass lapping to a viable procedure. If the gasket doesn't leak, Mad Science can claim the lapping worked
 
As others have stated, if the head bolts are too long, they will bottom out and give you a false torque reading while the head remains untorqued.
 
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