74 620 backfires out the carb

[datzenmike]

Why buy a $300 head in the first place????? Something wrong with what you have?

[sanyantho]

Why buy a $300 head in the first place????? Something wrong with what you have?

One of the valve is sinking on the head that I am running now.

[datzenmike]

OK know the one now.

[sanyantho]

OK know the one now.

Yes, you gave me an advice to shave the adjustment nut to allow more room to adjust the valve lash. It is working good with no problem. :thumbup: I will wait to replace the head. Thanks guys!

[wayno]

This might not be a good idea, the U67 head is an open chamber head, if your A87 head is closed chamber which it might be, you will significantly drop your compression ratio.

I would rebuild what you have, and have the shop put hardened seats in the head. 

[sanyantho]

This might not be a good idea, the U67 head is an open chamber head, if your A87 head is closed chamber which it might be, you will significantly drop your compression ratio.

I would rebuild what you have, and have the shop put hardened seats in the head. 

I hope thats not the case, I already bought a U67 head per Mike suggestion below. :confused:

 

Might be easier to just source a U67 head from any L20B. Larger intake ports and larger exhaust valves with square ports to match your L18 exhaust manifold.

[wayno]

I guess it depends on if your head is open or closed chamber, and if your L18 has dished or flat top pistons.

Lots of people giving advise on here, I think it is better to know what you have before advising what parts to buy.

Maybe it is already known what pistons the L18 came with, if the L18 blocks were all flat top, well then the U67 may be what you need, but from what I have read, the U67 came on the L20b.

I am curious, on the front of the A87 head, just below the oval timing chain inspection plate, is there a number?

[datzenmike]

Wayno no closed chamber heads came on any Datsuns that I know of. Probably thousands were imported by mechanics in the 70/80s because it was cheaper than rebuilding them. If you do the math an L18 with an open chamber head has 8.43 compression matches the L16 before and the L20B after. There would be no point to have a 9 to one compression L18 in the middle of the 70s.

[wayno]

So all closed chamber heads in the US came on imported used engines from Japan, or they were ordered from Nissan?

So what would the compression ratio be with a flat top piston(0 deck height with valve notches) with a closed chamber head? then an open head?

 

Wayno no closed chamber heads came on any Datsuns that I know of. Probably thousands were imported by mechanics in the 70/80s because it was cheaper than rebuilding them. If you do the math an L18 with an open chamber head has 8.43 compression matches the L16 before and the L20B after. There would be no point to have a 9 to one compression L18 in the middle of the 70s.

[datzenmike]

I've looked up the part numbers and all there are, are 210, A87, U67 and W58. Some L20Bs may have gotten the A87 but why not? they are the same size as the other two L20B heads, just smaller valves or ports. L18s seem to have gotten the same head, an open chamber A-87. Lots of A-87s are closed chamber, but most are open. If you had a stock L18 and the head was replaced with a closed chamber, the compression would be 9.0 to one. That's barely a half point of compression increase.