Schizophrenic Engine

Checking engine and seeing what bits need attention. New thrush washers are on the list. The engine was in a 74 six (CF 20065U) originally but I find the block (CC65650E) was somewhere in the middle of 71. The block clearly has the flat top, no recess around each piston. It looks pretty good, the cylinders measure out at original 2.94 so does not appear to have been bored out and cylinder walls are smooth. Some scoring on number 1 and the top of that cylinder looks like it had an encounter with a value stem at some point. The engine ran strong when parked 19 years ago, some dark smoke on acceleration. Now as I look closer, I find the cylinder head is later version with double springs. It is stamped 219019. Anyone know if that is a 7.75 or 7.5 compression head?

I have not seen anything that makes me think I can’t continue with this combination, IS THERE?

I would just like to address the basics to get going in stock condition right now. It is currently in a 73, I had swapped engine way back when, because this one ran stronger, but I can get the original engine back. I think I will it get this one going then get the original engine and do a full rebuild on it and kick it up a notch.

I got an early 71 with a GT6 head,so I'm sure yours is fine.

I've got a late block with an early head. You should be fine. The quick estimate of which head you have would be from Richard Good's (GoodParts) site. He says a head 3.539" thick gives 7.75:1 and a head 3.550" thick gives 7.62:1. Of course, you could have yours cut down if you wanted to raise the CR.

Bryan

The number 219019 is what is on my 1974 TR6 head. It's on the right front of the head as seen below.

Thanks, I was glad to see the measurements for thickness, we most always have to wonder what has happened before. Like why did a 1971 block end up under the 1974 head? I will check this one; I figure it should be a thicker one in 1974. I will probably take it out to a shop just to smooth up the surfaces. If I trimmed it down at what point would I have to shorten the push rods?

I had about 0.090" off of this head and it was at the end of the adjustment with stock rods. There will probably be another .020" - 0.030", minimum coming off, so I ordered shorter push rods for the new engine.

Read this thread: https://www.britishcarforum.com/bcforum/ubbthreads.php/ubb/showflat/Number/391883/gonew/1#UNREAD

And then this is the "unofficial-official" chart to use.

https://www.goodparts.com/tech_docs/TR6_Compression_Ratio.html

Good luck.....

Assuming the 74 head would have started at 7.62 compression, with .090 off the the yours should be 3.46 thickness.
Does that work out compared to what you have now?

I don't have my head here to verify that. SUPPOSEDLY, the previous shop was to get me to 8.75 to one, so your assumption is correct, if they indeed did do so. I know that the previous machine shop said that it only had a skim cut when I bought it. They took .080" off, so I gave the skim cut another .010" as a guess.

This time the head will be cc'd again (all valves are being redone) and matched to the new shaved deck with zero deck clearance. The head will then be machined to get me to 9.5 to 1 compression. My block was over bored 0.030", so that changes things a bit and I trust the machinist to do it perfectly this time. Until he does his calculations, and measures everything, I don't know what will really be coming off.

Thanks, right now I am just looking at my options without going to far. As a side note another thanks for your many great pics on the forum.

When you bored the block, did you put in the Mazda pistons?

I think the later heads are an advantage over the older heads when you cut them to the desired compression ratio.

No Ron, I did not. I got a great deal on new AE pistons fitted with rings from BPNW and went with those.