Honda CB750 Sandcast

Recent Posts

91
General Discussion / Re: Starting Work on CB750-1001250
« Last post by BenelliSEI on December 07, 2022, 11:17:14 pm »
Repairing a few bent fins will be the next order of business when the parts return from vapour blasting. The top end will get a light hone, rings and all new gaskets and seals.
92
New Member Introductions / Re: 9/69 twins
« Last post by Steve Swan on December 07, 2022, 08:56:14 pm »
Hey folks,
 I'm new to750 Honda . I've got two 69s. The funny thing is they were both built in 9 of 69, but they are 6 thousand apart.
one is 6740 and the other is over 12k. how can they make that many in a month?

Leonard, there is not a simple answer to your question.

Although nearly anything is possible with range differences between Evins and Fvins, to better understand your vin's it would be helpful if you shared the Evin/Fvin for each machine so the vin spread between engine and frame can be pondered. 

By Sept.1969, frame tags read mfgr date and frame number.  The majority of sandcast Evins will show the engine number on the vin pad and a casting date elsewhere on the case.  i can't speak with certainty to casting dates on pressure cast cases, but i'm somewhat certain pressure cast cases also have casting dates.

Assuming your one Sept.69 machine has non-sandcast cases, what would be interesting to know on those non-sandcast cases is what the casting dates are...  Without knowing the casting dates on the non-sandcast cases, it is not possible to know if the casting date is close to the time frame 12,xxx numbers were stamped on the cases at the factory.   If i recall correctly, by September's end, vin numbers  were not much higher than 9,xxx.  10,xxx numbers were seen around October and 11,xxx numbers during November 1969.

If my memory serves me correctly, engines stamped 12,xxx would have received that stamp late in the year 1969, likely December, perhaps, but possibly or unlikely, November 1969.  Assuming the 12,xxx number you refer to is the engine number, it might prove fascinating to know the casting date which one can, based on vin study experience, deduce could have a December or November casting date.

If the casting date on your 12,xxx engine is later than September, then a debate could take place why a post-September assembled engine is in a September frame.  Casual guess would be that a post-September set of cases replaced cast in September cases, i.e., the engine that came in your September frame got swapped out for a December engine; likely reason due to chain wadding.  If your 12,xxx cases have September or October casting dates (unlikely), an even more interesting debate of conjecture could occur.

What would be best is if you would post pictures of the Evins and Fvins so that the font can evaluated for factory authentic and weren't dealer stamped on a set of blank cases replacing broken cases.

In direct reply to your question, "How can they make that many in a month?" the answer, justifiably so, could be, "Not 6000." 

The longer answer would be that during the period of time when pressure cast cases began being used and sandcast cases were not longer used, production in October slowed considerably throughout and into November and as i mentioned earlier by December, 1969, vins were up to the 12,xxx range and by January, 1970 vins were in  the 20,xxx range.  That being said, from the last 7414 sandcast vin coming off the assembly line sometime September 1969 and 7415 being a pressure cast vin, 7415 plus 5000 more engines built would take us approximately your 12,xxx vin.  That being said, one could guess that 5000 engines were assembled sometime between mid-September and December 1969...  Mid-September 1969 to December's end 1969 is roughly 3-1/2 months, so 5000/3.5 = 1428 engines per month were produced, although this is unlikely as fewer units were produced in October than November and fewer units produced in November than December, so forth and so on.

In closing, a careful and thoughtful study of the vin registry accompanied with critical thinking will readily provide the student with somewhat of an approximate idea of production numbers on a monthly basis, in some cases during earlier sandcast production periods even on a bi-monthly basis.
93
New Member Introductions / 9/69 twins
« Last post by leonard on December 05, 2022, 08:18:36 pm »
Hey folks,
 I'm new to750 Honda . I've got two 69s. The funny thing is they were both built in 9 of 69, but they are 6 thousand apart.
one is 6740 and the other is over 12k. how can they make that many in a month?
94
General Discussion / Re: Starting Work on CB750-1001250
« Last post by BenelliSEI on December 02, 2022, 06:33:53 pm »
Chatted with Brian at Rocket Performance today. They are close to me, in Whitby, Ontario. The two major components pictured above will get my first test with “vapour blasting”. I’ve seen other stuff he has done, it looks like new when completed, with no alterations to base material.
95
General Discussion / Re: Starting Work on CB750-1001250
« Last post by BenelliSEI on December 01, 2022, 04:18:02 pm »
Moving forward again. Stripped the head today. “Homemade” valve spring compressor works well!
96
General Discussion / Re: Starting Work on CB750-1001250
« Last post by BenelliSEI on December 01, 2022, 04:15:18 pm »
Here’s a photo of the “lifting rig”.
97
General Discussion / Re: Starting Work on CB750-1001250
« Last post by BenelliSEI on November 30, 2022, 06:27:03 pm »
Today I added a pair of threaded rods sticking up from the angle iron bolted to the barrels. Built a bridging platform across the top of the head studs and pulled up with the threaded rods. Despite a tremendous amount of preload nothing budged UNTIL I super heated the base of each front stud where the dowel tubes are located. Several huge , scary hits with a brass drift and a 2.5 lbs. hammer and it finally “popped”. So pleased, I forgot to take a photo. Will take a few next shop day.
98
General Discussion / Re: Starting Work on CB750-1001250
« Last post by BenelliSEI on November 30, 2022, 06:20:45 pm »
Back to work on #582. I had this engine running nicely in the frame, before tearing down the bike. Great oil pressure, no chain noises, all good. Pulled the head and then got stumped..... the bore portion was solidly stuck to the cases. An I mean STUCK. Built a lifting frame and hung it from the rafters. Despite a ton of soaking, penetrating muck, etc., it would not come apart.
99
General Discussion / Re: Starting Work on CB750-1001250
« Last post by BenelliSEI on November 30, 2022, 06:13:46 pm »
So it’s been  awhile! The race season was a hoot. The LEXUS was new to our Team. It was built for the American Grand Am  Series by a group of Lexus factory engineers. It had not been raced in several years, so took us a while to sort. The tired race motor finally let go mid season and we swapped over the “tuned” head to a very low mileage, stock  motor. After that it ran like a train. It’s a big six, and has lots of HP and even more torque. We added a 20 gallon fuel cell so each of us could stay in the car for a full 2 hours (the races are 8 hour enduros). Power steering and brakes make it easier for long sessions, and the brute is fun to drive. Not as fast as some of the Porsches and newer imports, but very satisfying....

Took the Benelli 750 SIE to the Cobble Beach Concours, late Fall. No prizes, but a fellow from Florida took a real shine to it, so it’s headed there now. Also, sold the 1970 cb750K0 to a local guy who put +1000 miles on it. Completely stalled out on the Sandcast and Rickman CR projects, but getting back to it now.
100
Gauges - Levers and Cables / Gauge/Meter Restoration Hint
« Last post by kp on November 24, 2022, 04:27:42 pm »
If you intend restoring an instrument and want to use the same case here's something I do to refinish the rear plastic ring. This helps retain the innards and give an unmolested look to your restored part. Essentially it is just the method I use to remove the black retaining section of the gauge for future attachment. Photos say it all