Author Topic: Popular engine mods of yesteryear?  (Read 1165 times)

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Offline christopherk

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Popular engine mods of yesteryear?
« on: September 28, 2015, 06:47:57 AM »
Hey!

My CB750f1 has some aftermarket mods done to it. Previous owner mentioned it was "bored out," had a 620 chain conversion with shorter gearing, kerker exhaust, oil cooler, hi flow filters, etc. He also told me these were done "in the 70s." In the interest of reliability, i'm considering bringing it back to stock with the stock cylinder, air box, and a less loud exhaust. However, i'm wondering if by doing this, I might run into some internal mods that I wasnt expecting - rods, cam, etc - and i'm concerned of the impact on a stock setup.

Anyone know of some of the engine mods back then? Will they have an adverse effect on a stock setup? How would i be able to tell (markings on the cam, etc.)?

Offline BPellerine

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Re: Popular engine mods of yesteryear?
« Reply #1 on: September 28, 2015, 01:01:50 PM »
is it running now?if ok why bother.you would have to tear the engine down to see what you have at least the top end,you can measure the bores or maybe the size marked on top of piston,the cam might have markings under the washer,and may/may not run well with stock bore.bill
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Offline Garage_guy_chris

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Re: Popular engine mods of yesteryear?
« Reply #2 on: September 28, 2015, 03:11:00 PM »
These engines are very modification friendly. there was and still is a huge market of parts available to do so. Hp mods and reliability are sort of inversely proportional. as you add HP you are going to effect reliability. What you need to do is investigate and find out more. satanic mechanic has a large amount of info and insight to all the different mods available and will put things into perspective a little.

http://www.webring.org/l/rd?ring=thehondasohc4web;id=2;url=http%3A%2F%2Fwww.satanicmechanic.org%2F

In terms of "bored out" we need to know by how much are we talking a .025" oversize overbore or a 73mm 1060cc monster? It seems to me the most common over bore is a 64mm 811cc or a 65mm 836cc after that the $$$ increases drastically.  If in fact its a 811cc or 836cc reliability really wont suffer all that much just a modest 10-15hp bump

In terms of cams its very similar to bore a low lift, low duration cam will have almost no effect or reliability while a big fat high lift, high duration cam will most definitely effect reliability. A lot of cams will be marked on the end of the cam, on the shaft of the cam or on the edge of the sprocket boss. Although some will be a mystery cam with no marks and all you can do is measure lift and duration and try to match the figures to known cam grinds.

In terms of setup all this performance stuff really doesn't have any major impact on setup. Your spark timing will likely still be setup same as stock and carburetors will just have larger main jets and needle clips lower on the needles.

The best place to start is to take a outboard spark plug out and have a look with a borescope or inspection camera.
Second place to investigate is to remove a tappet cover and see if there is special valve retainer gear, 
Third place to investigate would be to pull a carb bowl and see what size main jets are in there, your F1 likely would have 105mains if you find 120, 125, 130's id say its likely you have a mild overbore like a 811cc or 836cc
Forth place is to pull the engine and remove the valve cover and inspect the cam for markings
Fifth would be to pull the head and cylinders for a look at the pistons and rods

here was the first hint of a not stock engine on my 750 2years ago.... Later i found out they were yoshimura 64mm 811cc pistons...
« Last Edit: September 28, 2015, 03:13:03 PM by Garage_guy_chris »
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Offline HondaMan

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Re: Popular engine mods of yesteryear?
« Reply #3 on: September 28, 2015, 04:18:12 PM »
Hey!

My CB750f1 has some aftermarket mods done to it. Previous owner mentioned it was "bored out," had a 620 chain conversion with shorter gearing, kerker exhaust, oil cooler, hi flow filters, etc. He also told me these were done "in the 70s." In the interest of reliability, i'm considering bringing it back to stock with the stock cylinder, air box, and a less loud exhaust. However, i'm wondering if by doing this, I might run into some internal mods that I wasnt expecting - rods, cam, etc - and i'm concerned of the impact on a stock setup.

Anyone know of some of the engine mods back then? Will they have an adverse effect on a stock setup? How would i be able to tell (markings on the cam, etc.)?

If the engine was internally modified, nothing you do externally will hurt it. Such external things as removing the Kerker, changing the chain/sprockets, or even removing the oil cooler won't detract much. The oil cooler does help with the oil temperature issues on the black engines, by cooling off some of the extra heat those engines suffer from the paint.

The 620 chain mod was a lightening strategy (saved about 1.1 lbs), as the engines don't make enough power to require a 630 chain (despite Honda using them). Even a fully-race-built 750 will make possibly 80 HP, and even a good-quality 530 chain will handle 100 HP with no problems. You will find far more parts available in the 530 or 630 size chain/sprockets arena.

The "boring out" ranges from a step bore of 0.25mm (740cc) to 836cc (65mm or +4mm) in stock cylinder sleeves. Some higher-compression pistons were/are available for these pistons, too. If the cylinders are larger than the 836cc size, there should be external evidence of it: pictures would help us identify that?

More rare in the '70s was hotter cams, bigger carbs or valves, that sort of internal stuff. Most of the time, riders would bolt on a lighter 4-1 exhaust system on the "F" bikes and maybe an oil cooler, then lie to their friends about the "boring out" they did, or the like.

Then, of course, there are the guys like our own Rxmangriff, who has gone to 1000cc and valves from my station wagon, with a cam that can feed a Formula One car...
(Right, Jerry?)

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Offline Retro Rocket

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Re: Popular engine mods of yesteryear?
« Reply #4 on: September 28, 2015, 04:26:42 PM »
Hey!

My CB750f1 has some aftermarket mods done to it. Previous owner mentioned it was "bored out," had a 620 chain conversion with shorter gearing, kerker exhaust, oil cooler, hi flow filters, etc. He also told me these were done "in the 70s." In the interest of reliability, i'm considering bringing it back to stock with the stock cylinder, air box, and a less loud exhaust. However, i'm wondering if by doing this, I might run into some internal mods that I wasnt expecting - rods, cam, etc - and i'm concerned of the impact on a stock setup.

Anyone know of some of the engine mods back then? Will they have an adverse effect on a stock setup? How would i be able to tell (markings on the cam, etc.)?

If the engine was internally modified, nothing you do externally will hurt it. Such external things as removing the Kerker, changing the chain/sprockets, or even removing the oil cooler won't detract much. The oil cooler does help with the oil temperature issues on the black engines, by cooling off some of the extra heat those engines suffer from the paint.

The 620 chain mod was a lightening strategy (saved about 1.1 lbs), as the engines don't make enough power to require a 630 chain (despite Honda using them). Even a fully-race-built 750 will make possibly 80 HP, and even a good-quality 530 chain will handle 100 HP with no problems. You will find far more parts available in the 530 or 630 size chain/sprockets arena.

The "boring out" ranges from a step bore of 0.25mm (740cc) to 836cc (65mm or +4mm) in stock cylinder sleeves. Some higher-compression pistons were/are available for these pistons, too. If the cylinders are larger than the 836cc size, there should be external evidence of it: pictures would help us identify that?

More rare in the '70s was hotter cams, bigger carbs or valves, that sort of internal stuff. Most of the time, riders would bolt on a lighter 4-1 exhaust system on the "F" bikes and maybe an oil cooler, then lie to their friends about the "boring out" they did, or the like.

Then, of course, there are the guys like our own Rxmangriff, who has gone to 1000cc and valves from my station wagon, with a cam that can feed a Formula One car...
(Right, Jerry?)

:) ;)

Modern superbikes with 200HP plus use smaller chains Mark, a good quality 520/525/530 will all handle big HP. Todays chains are far superior to the old 70's chains... ;)
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
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Offline mrbreeze

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Re: Popular engine mods of yesteryear?
« Reply #5 on: September 28, 2015, 06:09:54 PM »
And ask Fat Matt which is easier to find when your out doing the SOHC Godzilla tour and you're 300 miles from home.....a 630 or a 530 chain!!
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Offline Don R

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Re: Popular engine mods of yesteryear?
« Reply #6 on: September 28, 2015, 06:28:35 PM »
 Most of the big bore 750 I buy are in fact stock. Your mileage may vary.
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