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Discussion Starter · #1 ·
I'm trying to sort out the cylinder heads for year, model, part number. Honda used several part numbers for the heads and some are suitable for the high dome pistons where others are not. They are visually identified by the cast H number you see between the exhaust ports. What I have so far is 1978/79 CB400T 1 & 2 and 1979 CM400T use part number 12200-413-000 (superseded by 12200-413-890) which corresponds to the H2 head. 1980 CB400T, CM400E & T use 12200-447-670. The 1981 models all use 12200-447-750. There are at least 4 variants by H number that I've seen, H2 H3 H4 and H5, there's been mention elsewhere of up to 8 variants. I've never seen an H1 head but I'm sure that exists somewhere.
So if you have an original engine in your 400 could you supply the following information:
Production date from the VIN plate on the steering stem.
Country designation, US, UK, Canada, Australia, etc.
Year and model
H code from the head
 

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All from Canada :

1979 CM400T2 3/79 H-2

1980 CM400T2 1/80 H-2

1981 CM400T2 12/80 H-1
 

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Discussion Starter · #6 ·
The D8EA and DR8ES-L are both listed as 19mm thread length and neither is listed as projected tip. I don't have both on hand to actually compare them.
Going through the FSM all of the US 400's are supposed to run D8EA as the standard plug and Canadian models call for the DR8ES-L, I using the FSM marked HM1018 published 12/80. Another FSM I have for the 250T/400T without any marking or publish date shows the DR8ES-L as standard and the D8EA as optional but I suspect this FSM is for Euro models since the US never saw the 250 engine.
 

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I can see no physical difference between the two, Jim.

Spark plug Auto part Automotive ignition part Automotive engine part
Spark plug Auto part Automotive ignition part Automotive engine part Suspension part
 

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Discussion Starter · #8 ·
I didn't think there was any difference and NGK's data sheets don't indicate any. I know with the low dome later pistons Honda had a indent in the top of the piston for plug clearance but that wasn't for an interference problem I don't think. As the fuel mixture was made leaner to meet emission regulations there would be a hot spot in the area of the sparkplug which would cause melt down. It's possible that the plug actually fits further into the head due to the machining of the plug seat.
Doode, maybe you can check that. How far the plug extends into the combustion chamber.
I'm waiting to hear back from a salvage yard owner about which heads he has on the shelf, thinking of buying one of each version. Then I can cc all the different chambers, physically compare them and if I get ambitious build a basic flow bench and test each one. Winter is coming and looks like I may go on the disabled list for awhile. Appointment for knee replacement late Oct., possibly both knees.
 

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Discussion Starter · #10 ·
I haven't really looked at a 450 head other than service work. I did note that the H numbers start all over again. Not even sure how many variations there might be. Measure the H4 you'got and that'll provide more info.
 

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Hi LDR :D
just seen this thread, very interesting. Obviously you would be aware that the Hondamatic heads have a different numbering. I have had bikes with the HA & HB references although It was mensioned to me that there is also a HC version.
I assume that these are 250 heads with small valves etc. Keep up the good work;)
 

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Discussion Starter · #12 ·
I know when Honda switched from the 400 to the 450 they started numbering all over again, not a problem on those heads since they are easily identified visually. Hard to say about the 250's since we didn't get them until the mid 80's in the Rebel and Nighthawk
 

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Hi jim:D
This pic is out of my Hondamatic archive which shows the 250 & 400 head basic differences. One thing I have never checked is whether or not Honda used the 250 camshaft in the Hondamatic? As I have a spare 250 engine I might look at that someday. 250's are farely common in the UK.

The left hand head is the HA and the right hand one is the H4 manual head. funnily enough the compression ratio of the Hondamatic is only slightly lower than the manual, probably due to the "squish" effect using the 250 head on a 400 bore mainly.


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The flat top piston is for the Hondamatic and the other is a standard manual version.

Keep up the good work Jim;)

Cheers
 

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hi Jim:D
I would not be surprised if there is much in it, as plonking a 250 head on the 400 bore does not strike me as high tech more as a parts bin excercise. It would be nice to check the cam profiles against each other. Perhaps I am cynical but stamping a different set of parts numbers on the same item would solve a few problems for Honda. So would I if it was my decision, but I am not a samurai?:rolleyes:
 

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Discussion Starter · #16 ·
Actually Honda doesn't seem to do that. The center 3 numbers of the part number tell which model a part was originally designed for. We've got parts designed for other models from the 60's on the 400's. Honda Motorcycle Part Codes
 

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Wow, glad I looked on here! Replacing the head gasket on my 78 CB400TII I noticed some damage and wear on the cam and cam channel. Looked all over the usual places for a replacement for both but no luck. Saw on here the 79 CM400 used the same head so looked for that one, and sure enough, found one with the same marking (H-4). With the cam. I would've never thought to look at 79's, let alone CM's! Woohoo! Thanks!

So, yea, '78 CB400TII, U.S.A., stock engine, H-4 head.
 

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I didn't think there was any difference and NGK's data sheets don't indicate any. I know with the low dome later pistons Honda had a indent in the top of the piston for plug clearance but that wasn't for an interference problem I don't think..
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You will need a 1970's NGK catalogue to find difference. I had one but no idea where it's gone in last 30+ yrs. AFAIK, EA and ES-L have same running temperature (850~900f) but ES-L can get hotter without causing pre-ignition and dop not foul as easily in the 450~500 deg range ( from experience it seems to be right, EA will foul a bit easier with over rich mixtures but I've never had either cause pre-ignition)
 

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Hi Jim. Ive had both knees done but one at a time. At that time it was 5 days in the hospital but think its down to 3 now. To have one or both done at one time I think would depend on how much help you will have at home. To do both at the same time makes it tough to get to the kitchen or use the little boys room. I have a bathroom in my basement and put bars down from the floor joists to pull myself up and down on the john and in and out of the shower. you should be moving around pretty well in 5 to 6 weeks. Best of luck to you.


If your interested I have a head and cam from a 1978 CB 400A I can send you if it would help. Let me know .

Bill
 

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Discussion Starter · #20 ·
Thanks Bill for the offer. I will keep it in mind. So much going on with the Cochlear implant and learning to hear again is keeping me more than busy, I've had the CL350 torn down in nuts and bolts for the last 8 months and haven't touched it for @4 months now. Knees are on a back burner for a couple more years I think.
 
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