Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Alloy cylinder heads

Alloy cylinder heads

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Post Sat Feb 19, 2011 6:23 am

Posts: 41
I have 2 alloy cylinder heads for use on the 45 engine I am rebuilding. One of the head has a visibly deeper combustion chamber than the other. Is this normal or have I got two heads with different compression ratios? One head is marked with a 2 and F whilst the other has no such markings. Thanks, Joseph.
Head2.jpg
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Post Sat Feb 19, 2011 9:14 pm

Posts: 83
Maybe someone shaved one of them to fix a bad gasket surface; maybe the engine was put together with two different CR heads.
But...It doesn't matter if they were a matched set in the past or not. If they are visibly different (and I agree they are) you should correct this. First try to mesure how much water they can hold. If the difference is higher than 5% I think you should consider milling the bigger head so they can hold the same amount of liquid. Panic's 80 performance book has a very helpful table, but i'ts for BTSV, not the 45...maybe his 45 book has the same table...It will help you to determine how much to mill the heads. And try to find a good machinist, because those aluminum head fins will break easily in the wrong hands. Good luck!

Post Sun Feb 20, 2011 2:37 pm
jib

Posts: 575
Location: devon,england
used a burrette with parrafin to measure as it doesnt 'wet ' like water and less miniscus. and milling machine to do mine. used 3 engineers screw jacks and standard clamps to hold then level and secure to the bed
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years

Post Thu Feb 24, 2011 9:39 am

Posts: 41
Thanks for all your advice, scored another one through ebay. Seems ok in the photos, will measure the capacity when I receive it (will be some time though as its going to a friend in the US). Was not comfortable with milling the front one down as I don't think these were ever meant to be high-compression motors anyway!

Post Thu Feb 24, 2011 12:22 pm
jib

Posts: 575
Location: devon,england
running mine at about 6.5:1 , they made 6:1 harley ones and you can buy aftermarket 6:1 as well
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years

Post Thu Feb 24, 2011 2:49 pm

Posts: 41
Hello Jib, any idea what the heads marked 2 are in terms of compression ratio ... unless they have been milled down of course? Regards, Joseph.

Post Thu Feb 24, 2011 5:38 pm
jib

Posts: 575
Location: devon,england
joseph, show us a picture, dont think ive seen one with a 2 on it .
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years

Post Fri Feb 25, 2011 12:39 am

Posts: 41
From what I've read, the alloy heads were marked either 5 or 6. The 2 I'm referring to is visible on the top part of the second photograph I already posted showing the underside of the front head which I have. On the rear head I've just found on ebay, the seller's photos also show a 2 on the underside but only now I'm also noticing a 5 on the side which I think refers to the compression ratio.
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Post Fri Feb 25, 2011 11:39 am
jib

Posts: 575
Location: devon,england
the 2 looks like a mold marker.
the 5 is a compression marker.

you will have to measure and probably adjust the combustion chamber volumes if using mismatched heads.
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years

Post Fri Feb 25, 2011 2:29 pm

Posts: 41
Thanks for the advice Jib, that's what I intend to do. Regards, Joseph.


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