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New Thread - decking 1500 heads

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JPSmit

JPSmit

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Starting a new thread as this is not directly relevant to Morris' situation.

Hap you wrote this: "I'm a little late on the scene as i read this, I assumed you had a 1275,and i think other did as well, but then you said a mouthful, that threw up a bog red flag with me "I have a 1500", and "I had the block decked". The 1500 engine had what was supposed to be a improved head geasket with extr cylinder fire ring material aorund the bore of the gaskets with recessed area on the block for the eatra fire ring to compress in. Ok most would think, including my self this would be a good improvement to engine to not blow head gasket, but 1500 and TR6 engine with the same block recession have long had head gaskets problems, and one big no-no is excessively decking the block because if you mill more off the block than say a "clean up" of .005-.010" you lessne the amoutn of the recession in the block and this compromises head gasket seal, if you cut too much off the block and the recession is lessen to certian point the head gasket will not even seal anymore.

Not probably what you want to hear, but I betting your block was decked enough to compromise the gasket recession in the block and it causing your head gasket to fail long before they should , it could be worse, and not have sealed at all, I seen this firsthand, my advie would be just repalce head gaskets from time to time or worse, start over another block with good straight block deck. I'm sure this is not what you want to hear, but decking a 1500 block is always a bad idea, because of the head gasket design."

I have also head you talk about decking the head for TR6 pistons. Can you explain a bit more about this (Perhaps even addressing Billy's question about a 1300 gasket.

Thanks!
 
You can deck the 1500 engine to remove the recession and go with the earlier head gasket for non-recessed engines. BUT, you may need to deck your pistons too. I've heard both sides of the story...Recessions are good, recessions are bad. I don't know first hand. If you deck the block at all, you need to address the recessions the same amount.
 
Here's a fantabulous chart for 1500 heads, combustion chambers volumes and compression ratios w/ different pistons. Note the link for the spread sheet to figure how much you need to cut on what head with what piston to get whatever ratio you're after.

My plan was to deck the recess out of the block, open up the combustion chambers to make up the difference and unshroud the valves while I was at it.

https://www.triumphexperience.com/phorum/read.php?8,717989
 
kellysguy said:
My plan was to deck the recess out of the block, open up the combustion chambers to make up the difference and unshroud the valves while I was at it.

https://www.triumphexperience.com/phorum/read.php?8,717989
Click to expand...

I just had a 1500 block machined. Machinist noticed the block recess (I mentioned it as well) and we decided to just take a tiny skim off to clean it up if needed. Be aware, the recesses fill up with carbon, you'll want to make sure to clean these out so the fire ring has a place to squish. Even after cooking the block, I had to scrape the carbon out with a kebab skewar and a toothpick.

If you machine the recesses off, I believe you also need to machine the piston crowns down the same amount or you'll risk breaking the top ring. I believe a STD TR6 piston works for a .040 overbore on a 1500, but I'm too lazy to look that up. :smile: Still need to machine it if you deck the recesses away.
 
Scott_Hower said:
I believe a STD TR6 piston works for a .040 overbore on a 1500, but I'm too lazy to look that up. :smile: Still need to machine it if you deck the recesses away.
Click to expand...

Hap and others have mentioned this in the past and also said that the block would need to be decked to reestablish the compression ratio since the TR6 pistons are shorter. So I was going to brings up this question anyway so this seems like a good place to do it. Why use TR6 pistons to get a .040 over bore when you can find 1500 pistons that are .040 and .060 over anyway? Was it just an old school way to get .040 over when the pistons weren't available?
 
RichBall said:
Scott_Hower said:
I believe a STD TR6 piston works for a .040 overbore on a 1500, but I'm too lazy to look that up. :smile: Still need to machine it if you deck the recesses away.
Click to expand...

Hap and others have mentioned this in the past and also said that the block would need to be decked to reestablish the compression ratio since the TR6 pistons are shorter. So I was going to brings up this question anyway so this seems like a good place to do it. Why use TR6 pistons to get a .040 over bore when you can find 1500 pistons that are .040 and .060 over anyway? Was it just an old school way to get .040 over when the pistons weren't available?
Click to expand...

Dunno really. I'm using 1500 County 9:1 flat tops (.020 over)on my rebuild, they're available everywhere and fairly cheap (under $200). They have better rings than the AE/Hepolite repros. This yields about 8.6:1 on a low compression head. Plan is to skim the head about 50 thou to get it to 9:1
 
You have to cut like .250" off a 1500 block to use TR6 pistons, and it start getting close to the freeze plugs on the rear of the block,, can it done, yes, I've done it twice, but it take alot of work and custom length pushrods to pull it off. On cutting the recession out of the block and then trying to remove the needed amount off the 1500 pistons, I've never done that, but it would proably take a good .060" + off the pistons to make that work, and you have to worry about crown thickness on the psiton, if it gets too thin, it going to be issue, the top of the piston take alot heat, crown thickness help to disapate thet heat, I would not do it for customer unless he excepts all the risk involved. I think the best way to build a hot 1500 is deck the block recession out and then make custom forged pistons for it, not cheap but it would the best way to do it.

Yes a TR6 std. piston is .040" for 1500.

OH and you can cut the crap out of 1500 heads, I cut as much as .100" off them with no issues whatsoever,and racers have cut them as much as .200" to get real high compression.
 
billspit said:
I would have sworn that you had to cut (deck) TR6 pistons to go in a Spitfire. Guess i learned something tonight.
Click to expand...


Yep TR6 pistons have a much shorter compression height than 1500 pistons.
 
Yes. You can take 0.125 off the 1500 head with no problem. I ran that setup for 7 years. Stock pushrods and rocker arms too, by the way (and a Kent cam).

One time I measured the head chamber and with the AE pistons, I ended up with 10:1 compression ratio (which was plenty for my little hobby racer).
I never decked any of my 1500 blocks, even though they didn't look that great.....I didn't want to touch that machined recession.
 
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