BT-7 tri-carb ring gap

well i was rolling right along today until...

i went to gap the rings.

ring gaps for all compression rings (checked at least one from top, 2nd and 3rd groove) in all cylinders was pretty consistent. problem is they all were between .022 and .024.

the manual calls for .013-.018. my cylinders have been honed but not bored. i had the maachine shop check the bore while they had the block. they said they were all standard. i just went back out and checked them with my bore gauge and it showed 3.28, which means i am off a little i guess.

either way it looks like the cylinders are standard. these are hastings rings from Moss. part numbers on the box look correct as do the stickers put on by Hastings.

any of you all run thru this before? anything else i can check?

Just put it together says my cynical side. After all it's only an automobile engine, not a ROLEX. Do you really think that .01 is going to be the difference between life and death ? I admire your desire to get it"right" but you don't have many choices. One is to bore your engine to the next oversize and start over. Second is to try a different brand of rings . Third is to use what you got. Seems like only one obvious answer to me. (But what do I know, I only work on Chevrol.et

I tend to agree with Bob, it probably won't matter. I may be wrong on this but what I remember from my training (many years ago) put more emphasis on not having too small a gap and risking the ends butting together because that would lead to premature failure.
However, one solution I recommend is to buy Total Seal gapless 2nd compression rings. Not sure if this is still possible but you used to be able to buy just the 2nd compression ring and use the rest of the stock set.
I have had great success with Total Seal gapless rings and will not build another motor without them. Many times leak-down testing has proven to me that they really work well.
I think it's been several years since I bought a set but they weren't that expensive - particularly if you plan on keeping it for a while.
Dave

Its a glorified tractor engine not a Ferrari or Aston Martin Make sure none of the ring gaps line up with each other and build it .

Check the ring gap in the bottom of the cylinder and compare it to the gap at the top of the ring travel . That will give you an idea of how much taper the cylinder has. I agree , the end gap is a bit high but better that than too tight. Are the pistons new ? A lot of these I've seen the pistons were just too worn out in the ring lands to reuse.

brinkerhoff
good point on the taper since the cylinders were honed and not rebored.
sent you a pm.
Thanks

I was going to suggest getting a set of "gap to size" rings from Total Seal. I'm also a big fan of their gapless ring design, but SPECIFY that you want the closing rail with a SLANT GAP.

I don't know how many engines I've built since 1984** but all of them have Total Seal rings in them.





** I haven't kept accurate records, but I'm probably somewhere around 125-130 automobile engine buildss for a lifetime total, including this one I just put together a couple weeks ago

red57 said:

I tend to agree with Bob, it probably won't matter. I may be wrong on this but what I remember from my training (many years ago) put more emphasis on not having too small a gap and risking the ends butting together because that would lead to premature failure.
However, one solution I recommend is to buy Total Seal gapless 2nd compression rings. Not sure if this is still possible but you used to be able to buy just the 2nd compression ring and use the rest of the stock set.
I have had great success with Total Seal gapless rings and will not build another motor without them. Many times leak-down testing has proven to me that they really work well.
I think it's been several years since I bought a set but they weren't that expensive - particularly if you plan on keeping it for a while.
Dave

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appreciate all the suggestions. but no matter which rings i would use, they need to gap in some way i would think.

update:

based on what Brinkerhoff suggested and what i could read on ring gapping from the Hastings website, i took some measurements to check for taper in the cylinders. fortunately, i guess, they are all at least very consistent.

first i measured below where the rings go so i could get a base line, so to speak. i used the same ring in each cylinder so i would be consistent.

so once squared the gap at this point was .018 to .019 / right at the top of the scale without any wear issues.

then i measured at 3-1/2" from the top of the cylinder i got measurements of .019-.020
then at 2-1/8" from the top i got .020 - .021
then 1" down from the top i got .022-.023 / i think in two cylinders i could drag .024 thru with a little effort.

now if i take the same rule of thumb that .001 change in diameter will affect .003 in ring gap and work backwards, my worst case scenario says there is app .002 amount of wear in the cylinders. Reading from Hastings page they recommend staying under .003 per inch of diameter. in short any gap change under .009 for these cylinders is ok and within specs. that is if i am reading this right. https://www.hastingspistonrings.com/tech-tips-faqs/checking-compression-ring-gaps

From that i would think cylinder wear is not an issue here.

also today i had a guy call me from CA. the Moss technician had asked him to call me. he obviously builds Healey engines and had run in to this before. first thing he asked me was... are the rings you have from Hastings. they are. he said he had run in to this a couple of times and that Moss had replaced them with Grant rings and the gaps were fine. So i have sent another note to Moss to see if they can still get the Grant rings and i have also called Grant to see if i could purchase a set of P1098 rings. waiting to hear back.

another update.

just got off the phone with the guy from Grant. He said he believes his rings are very similar to Hastings and he would not buy a set from him hoping they would help the gap.

also talked with Total Seal. he suggested i send only my second groove rings to him and they would make them in to gapless rings. takes 24 hours and i think he said total cost of around 70 dollars plus shipping out and back.

the guy from Grant also quoted a study done in Europe where they tested rings with gapping up to .060, he said they found very little extra oil usage and very little HP loss or at least not near as much as they expected. Not sure what that means.... haha

Anyway, all the info i got right now. time to make a decision...

also talked with Total Seal. he suggested i send only my second groove rings to him and they would make them in to gapless rings. takes 24 hours and i think he said total cost of around 70 dollars plus shipping out and back.
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Click to expand...

For me, that is a no brainer - problem solved, and for less than $100!!

well i thought about this for a night.
everything i read suggests i would probably be ok with using the current set of rings the way they are. but... everyone i talked to did not really like the extra gap.

so i sent the rings out to Total Seal today. heck i spent the extra money for better valve seals, why wouldn't i do the same thing here.

with all the good reviews and responses i got on Total Seal it seems like a good gamble. actually my only real draw back was that i would have a week with nothing to work on.

So like red57 said, "no brainer".

maybe i can pass the time building a rear shelf / storage compartment to replace the rear seats....

thanks all for the info and help.