Author Topic: no wonder it seized up! (Read 18387 times)

spitfire · « **Reply #75 on:** April 17, 2007, 04:41:58 AM »

Hi Mick,
The pistons do look different, see attached pictures of my F1 engine (1976), I know they are stock since I have owned the bike since new and this was it's first strip.

Cheers

Den

mcpuffett · « **Reply #76 on:** April 17, 2007, 08:12:56 AM »

Don't know then the engine is out of a f1 registered as a S reg 1978 ( i have the complete bike) and i know that it is standard bore as i had to order piston rings from cmsnl after i broke 1 putting it back together , i also have some pistons out of a k7 that look like yours Den and they are numbered as 300's , maybe someone who knows these motors might shed some light on it ? cheers mick.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #77 on:** April 17, 2007, 11:11:10 AM »

I'm with Spitfire on this. I bought my 75 750F0 in 3/75. I have the same pistons he has. I recently took my spare 1978 750K8 engine apart expecting to see the same piston. However, it has the earlier style that you would find the the earlier Ks. I was also surprised to see that both are -392 pistons??!! The compression ratio was bumped up to 9.2 to 1 beginning with the 75 750F. The 77 & 78 Ks are also listed as 9.2 to 1. The 75 & 76 Fs use a -392 head as do the 77 & 78 Ks. What I don't understand is how are these Fs and Ks "rated" at the same compression ratio using the same heads but different pistons. The piston Spitfire has pictured is going to have a definite increased compression ratio since it does not have the 5mm relief around it and the dome heights are the same. I would have to come to 1 of 2 conclusions. If the 77/78K has a true 9.2:1 CR then the 75/76F is actually higher -OR- if the 75/76F has a true 9.2:1 Cr then the 77/78K is actually lower. In any case if I had the choice I would use the pistons from a 75/76 F.

What is the engine serial number? Where are you guys located? Keep in mind also that some of the F1s had slight differences depending where they were exported to. I'm in the states and from what some of the guys have shown there were exterior differences from our bikes and the British and OZ versions.

You're pretty good with the camera. How about giving me a close up of the head. I'd like to see the top fin area between #2 & #3 on the intake side. What I would be looking for is 392. If your engine serial number truely indicates it is a F1 but you do not have a 392 on the head then what you have is a hybrid that was put together from different engines. Perhaps it is a K engine that was put into a F1. I blew my engine in '76 and I had that option which I decided not to do.

mcpuffett · « **Reply #78 on:** April 17, 2007, 12:46:24 PM »

Hi heres a picture of my head and it clearly states 392 , $:-\$ , maybe it was a friday afternoon speciael ;

i will check the engine number tomorrow as i don't have it at hand , cheers mick.( also heres a couple of pics of pistons the same as mine).

mcpuffett · « **Reply #79 on:** April 17, 2007, 12:59:53 PM »

heres a better picture of the head

Jerry Rxman Griffin aka MuthaF'er · « **Reply #80 on:** April 17, 2007, 01:22:16 PM »

So far so good. More like my K8 than my F0 due to the pistons. Same -392 pistons as my K8. Same head as both. My K8 head had K8 hand stamped on it in close proximity to the 392 casting probably to differentiate the K8 springs, retainers, and keepers that the K8 went to. I'd like to hear from an original K7 owner as to pistons and head markings. I'm leaning towards your engine being a K7 unless it has the K8 stamping. I'd bet that a K7 head is totally identical to a F0 or F1 without a K7 stamping since the valve train is totally identical.

I do need to qualify that I am not the original owner of the K8 engine. It does not look like it's been apart before though. I can't be 100% since I did not purchase it new.

mcpuffett · « **Reply #81 on:** April 17, 2007, 01:46:49 PM »

Hi jerry , its a bit of a puzzle my engine number is cb750e2561660 and i am in the uk, my f/f1 parts book shows it as being a f1 and in the parts book it lists both types of piston for the f/f1? cheers mick.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #82 on:** April 17, 2007, 04:37:04 PM »

Interesting to say the least. I would say yours is definitely a F1 engine from the serial number. However I would also say that it is probably the precursor to the K7/K8. I opened up Service Honda's microfiche and it lists piston 13101-392-000 as the only number for 75 & 76. It shows that piston number was installed up to serial number 2551567. Perhaps mystery solved? Still makes no sense why they both would be tagged as 392 on the skirt and be different?! Honda secret weapon perhaps?! I knew mine ran extrordinary before I blew it up. It does not show a different number for pistons after 2551567. Glad I got mine before the change except for the fact I blew it up in 3/76. Coincidence? Can't blame Honda. Naw, I was drinking (etc) and riding and missed a power shift to 2nd. Anyway, I guess I'm now the proud owner of 3 extinct higher compression pistons that are somewhat rare. I'll save them in case someone needs a spare since I'm running 810 Yosh as replacement and will be doing a 900 kit this next winter.

Sam Green Racing · « **Reply #83 on:** April 17, 2007, 05:38:20 PM »

I think about 99.999% of Hondas are Friday afternoon specials

.....they used a system called the parts bin method.

If during assembly they ran out of parts, they would use parts from another model as long as it fit OK.

Sam.

mcpuffett · « **Reply #84 on:** April 18, 2007, 01:29:33 AM »

This is better than an episode of mythbusters

, sory won't see you at stafford sam but i'm going to come over to elvington when you are running there

, cheers mick.

spitfire · « **Reply #85 on:** April 18, 2007, 10:55:47 AM »

I think mine was a Friday afternoon bike, it's never been stripped before but I found some odd things when I stripped it, the inner mudguard had a chunk missing where you could not see it without tearing the bike down, and one of the the rider footrests certainly looks nothing like the one in the parts manual.
Mine like Mick's is a UK bike engine number CB750E2549119.

Cheers

Den

Jerry Rxman Griffin aka MuthaF'er · « **Reply #86 on:** April 18, 2007, 11:13:40 AM »

Don't the UK bikes have the older style smaller turn signals and 2 supports for the front fender rather than 1 like the US bikes have?

Sam Green Racing · « **Reply #87 on:** April 18, 2007, 11:39:34 AM »

Quote from: spitfire on April 18, 2007, 10:55:47 AM

I think mine was a Friday afternoon bike, it's never been stripped before but I found some odd things when I stripped it, the inner mudguard had a chunk missing where you could not see it without tearing the bike down, and one of the the rider footrests certainly looks nothing like the one in the parts manual.
Mine like Mick's is a UK bike engine number CB750E2549119.

Cheers

Den

Dennis,

is yours an F1 or F2, also when was it registered ?
Mine is an F2 registered in 76 on a R plate with an engine number 588,476 later than Micks. Micks is an F1 registered in 78 on a S plate

It would seem Micks bike sat in a dealers for a few years before it was sold.

Sam.

mcpuffett · « **Reply #88 on:** April 18, 2007, 01:28:25 PM »

Thats the conclusion i had come to , that it was registered later because i'm sure F2's were out by then ?, my other f1 the black one is a P reg 1976 same as Den's , cheers mick.

Sam Green Racing · « **Reply #89 on:** April 18, 2007, 01:40:26 PM »

But we are still unsure what sort of pistons you have in it

Sam.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #90 on:** April 18, 2007, 02:17:59 PM »

Sam,

When you guys are talking about F2s are you talking about the black engine, comstar wheels, dual front discs, etc? That would be a 77 model (ser # beginning with 2600004) and the F3 would be the 78 model (ser # beginning 3100001). The 77 F2 had the same side cover emblems as the 75/76 while the 78 F3 had different side cover emblems.

These are obviously different than the 75 F0 (ser # beginning 1000002) and the 76 F1 (ser # beginning 2515094).

These serial numbers are for engines and not frames.

I have pages out of the Honda Indentification Guide if you'd like to see these. Too bad there isn't a friggin piston guide too!

mcpuffett · « **Reply #91 on:** April 18, 2007, 02:38:52 PM »

,

Sam Green Racing · « **Reply #92 on:** April 18, 2007, 02:39:14 PM »

Quote from: RxmanGriff on April 18, 2007, 02:17:59 PM

Sam,

When you guys are talking about F2s are you talking about the black engine, comstar wheels, dual front discs, etc? That would be a 77 model (ser # beginning with 2600004) and the F3 would be the 78 model (ser # beginning 3100001). The 77 F2 had the same side cover emblems as the 75/76 while the 78 F3 had different side cover emblems.

These are obviously different than the 75 F0 (ser # beginning 1000002) and the 76 F1 (ser # beginning 2515094).

These serial numbers are for engines and not frames.

I have pages out of the Honda Indentification Guide if you'd like to see these. Too bad there isn't a friggin piston guide too!

Jerry, mine is the F2 as you described it but but it was first registered in 76 frame number 1025247. My motors number is 3150133 making it an F3.

Sam.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #93 on:** April 18, 2007, 03:44:04 PM »

Sam,

Hybrid. Does it get better mileage?

.

My pages list the 75 F0 as having frame numbers starting with CB750F-1000002 (mine is CB750F-1001606) and the 76 F1 as starting with CB750F-2000003. I know Honda did not produce 25247 F0s since they were built for perhaps 5 or 6 months at the most before they came out with the 76 F1. The 77 F2 frames were CB750F-2100011 & up while the 78 F3 frames were CB750F-2200001 & up.

My next question to you would be - does your VIN plate start with CB750F or CB750 ? If it doesn't have the F then you may have a K frame with a F2 engine. I think we may make liars out of the ID guide at this rate and it's Honda not Clymers?!.

This stuff gets stranger as we go. I'll attempt to scan and reduce the identification pages and post them.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #94 on:** April 18, 2007, 04:24:21 PM »

My computer skills suck but here goes. Wish I could get better resolution and stay within the file size limit without having to learn how to use an external source. You wouldn't believe how difficult this was for me!

Sam Green Racing · « **Reply #95 on:** April 18, 2007, 04:35:53 PM »

Perhaps the numbers we have over here don't equate to the numbers you have.

Sam

spitfire · « **Reply #96 on:** April 19, 2007, 07:16:38 AM »

Hi Sam,
My F1 was first registered in April 1976 (P plate), my F2 was registered in August 1977 (S plate), don't have a picture of the F2 whole as I bought it as a basket case, comstars, black engine etc.
There is a picture of f1 when new in my gallery, here's a picture of it "as bought" apart from the Dunstall silencer.

Cheers

Den

Jerry Rxman Griffin aka MuthaF'er · « **Reply #97 on:** April 19, 2007, 10:32:25 AM »

Hey guys,

What are S plates & P plates?

Sam Green Racing · « **Reply #98 on:** April 19, 2007, 11:43:05 AM »

Jerry, when a bike is registered it is given a licence plate the same as you have in the States.
The letter refers to the year it was registered. P shows the bike was first registered between 1st August 75 and the 31st July 76.

Sam.

spitfire · « **Reply #99 on:** April 19, 2007, 11:56:56 AM »

In the UK when you register a vehicle you are issued with a registration number which contains an indicater of the year the vehicle was first registered, this started out in I think 1963, in those days bikes had to carry number plates front and rear displaying the registration number.
Vehicles registered in 1963 had three letters, three numbers and then the letter A, which signified the year, the letter changed alphabetically year by year, my BSA was registered in 1964 it's registration number is BDM 822B. Hence by 1976 my Honda was on a P plate, PFM 212P. If my fading memory serves me right the first three letters signified the area that the vehicle was first registered in.
So from the registration number you can get a rough idea of how old a vehicle is, however to confuse the issue new vehicle registrations started in August so from just (I think) looking at my registration number the vehicle could have been registered from August 1975 to August 1976.
Some letters that could be confused with numbers where not used "O" for example, when the end of the alphabet was reached they just started from A again but reversed the position of the three numbers and letters, for example my 1990 Ford was H761 LPU.
Hope this is clear, if not I'm sure some other Brits will chime in !

Cheers

Den

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Author Topic: no wonder it seized up! (Read 18387 times)