Took a road trip yesterday to pick up a bunch Interceptor stuff . Guys says the motor had exhaust cams in for intakes and it went like stink ( before he crashed 25 years ago ) I seem to recall reading something about this but can't remember where . Is this for real and if so what are the upsides and or downsides ? And lastly how could you tell without having the technology to measure the lobes ? George
I've heard stories that the old machinery used by RE to make cams left a little to be desired as far as continuity is concerned. Some cams were made aftermarket in the USA and who knows what grind they were or what kind of machinery made them.
I know that the exhaust cam swap was done at Royal Enfield in 1958 to pep up the Indian Trailblazer. Earlier models list a separate intake cam part number but the 58 & on list the exhaust part number for both. As for the Interceptor I don't know. I would have to do some research there. The Apache and the Connies had hotter cams for a while but suffered problems with breakage under hard use to they backed off on the later 700 motors. The Interceptor 750 motor was buit to be stong enough to take hotter cams but I'm not sure how far they went with the grind.
My J2 runs an exhaust cam on the intake. It runs fine but it came that way so I don't know if it runs better or not. The reason it is done is because the exhaust lobe is much more rounded than the intake giving more opening duration.
Timing was a little tricky since the dot on the cam gear was in the wrong spot. I had a G intake cam for comparison and created a new dot where it should be. That is also when I discovered that the G cams do not interchange.
Hi, George! Welcome to the la-la land of Twin camshafts! So far I have not definitively come up with any accurate annecdotal info about cams fitted to the various year model twins. The parts books/numbers indicate some differences, but I'm still looking for more accurate info. Some are described as sports cams, others with quieting (!!!) ramps, etc. And, yes, many claim that the "sports cams" in 58 lead to many a blow-up! I just dunno!!! Seems like I already posted this once a while back, but this is a fact from my wierd life: In 1965, I once bought a set of "Apache camshafts" from my local Indian/RE dealer for use in my 57 Indian Trailblazer based drag bike. I do remember they were in Indian boxes and brown paper. Too bad I did not save the boxes among all the other insignificant crap I saved over the years!!!! But they did make a significant difference in performance! But they were not the only changes made to the engine. I still have the ported and polished heads from this machine sitting on my shelf! And I still have the nostagic dream of re-creating a clone of that bike. If I can find the pieces! Which brings us back to the cam question. Hitchcock's is offering new cams of different profiles, but what was the original application? I,too,have also heard of running Exhaust cams as Intakes for a performance boost. Somewhere, someone must remember something accurately! The big twins were actively campaigned on 1/2 mile/ mile & TT tracks back in the day, so performance modifications were commonplace. Shell Thuett built some really strong single & twins for Elliott Schulz back in the 60's. Maybe someone on the forum has some articles about those bikes & of course there were some Bonneville & drag bikes out there as well. The other alternative is to sit down with a degree wheel, dial indicator, and a great deal of patience to figure this all out! Maybe some of the old american cam grinders are still out there...or at least still have their specs & blueprints... Maybe further discussions on the forum will provide more info!!!
Twin So do you have any pictures of this drag bike you could scan and post . Love to see it . As to the cams I'm such a newbie I have no clue . But somebody somewhere must know . Course we are talking 50 years . I sometimes forget that. Maybe a post on Hitchcocks board would bring something out of the woodwork . George BTW Would Shell Thuett have anything to do with Shell Motors in California . If so see my Interceptor post .
I checked all the Parts books and Hitchcock's web-site and I could only find the two basic sets of cams for the 58 through 63 big twins. 32705 exhaust with 32706 intake for all the Regular performance twins. The 57 through 59 Indian Trailblazer/Chief parts calls for use of the 32705 for "both cams" on those motors with the exception of the Apache which uses the second generation performance cams P/N 35344 inlet and 35345 exhaust which was used on the Connie and even the series 1A Interceptor. The series 1 Interceptor 1963 parts book lists the old 32705/A cam for both inlet and exhaust but I don't know what the /A designation means. I'm sure they were both exhaust cams though. Hitchcock's list the old P/N number cams and the newer P/N cams plus the series II cams as new recent manufacture. I'm sure they are probably a more consistant and accurate grind cam than the originals were plus the hardness was probably better controled than all the old stuff.
It's surprising that they basically used the same cams with only two choices for the late 700 and the early 750 motors.
Hi, George and all!!! I think Shell Motors was the west coast distributor for RE...perhaps Indian...not 100% sure, though. Lots of misc. info on the Internet about both...tuner Shell Thuett and dealer Shell Mtrs. I don't know if there was any relation, though. Thanks to Greg (of this forum) & his friend Robert, I finally located a set of dual carb manifolds for my re-creation of the above mentioned Drag bike... Unfortunately, I have no pictures from those early years.... but, once I get enough bits together I will (learn to )post a photo of the clone mock-up. I am still missing some significant pieces such as the above mentioned cams, GP carbs, an unobtainable (my budget!!!)front end & front wheel, other odd bits... You fellows have done well locating those project bikes! It really helps the motivation factor to see them in one piece!!!! I am sure each one has an interesting story to tell!!!
[QB}Originally posted by rotorwrench: The series 1 Interceptor 1963 parts book lists the old 32705/A cam for both inlet and exhaust but I don't know what the /A designation means. [/QB]
I wonder it the "A" refers to the high performance intake timing sprocket, which had an "A" stamped on it. This differed from the standard intake sprocket in having the keyway cut so as to alter the intake timing.
This is defined on page 11 of my 1964 Interceptor factory shop manual in a table showing timing specs and camshafts for the three performance options available. It indicates that the 32705 cams were used for intake and exhaust in the #1 "standard" performance option. "Cams have quietening ramps. Least mechanical noise. Good torque and speed." This used the inlet sprocket 36140
The 35345 (ex) and 35344 (in) cams were used in both the two higher performance options.
The #2 sports option says "Better torque that #1. Same maximum speed. Noisier." Same inlet sprocket as #1.
The #3 sports option says "Torque as #1 up to 80 mph. Better than #1 or #2 above 90 mph. Noisier than 1. This used inlet sprocket 45207 (marked "A"), which is, I presume, where the "A" designation you're referring to came from.
My parts book is listed as for both 1963 and 1964, and they list the same number for the 1963 parts as your book, with the 353.. numbers being for the 1964 models. I think the use of the "A" intake sprocket offered better performance from the older cams, while the newer cams were better performance yet, even with the intake timing of the "non-A" sprocket.
As long as I'm quoting from that little table in my manual, I might as well list the timing specs given.
option 1 ex. opens at 82 deg. bbdc ex. closes at 35 deg. atdc in. opens at 35 deg. btdc in. closes at 82 deg. abdc option 2 ex. opens at 77 deg. bbdc ex. closes at 35 deg. atdc in. opens at 37 deg. btdc in. closes at 60 deg. abdc
option 3 ex. opens at 77 deg. bbdc ex. closes at 35 deg. atdc in. opens at 22 deg. btdc in. closes at 75 deg. abdc
Interestingly, it seems the "A" sprocket actually retards the intake timing. I guess it's more important to keep the valve open longer at the bottom of the stroke than it is to open it earlier near the top of the stroke.
Re: Exhaust = intake ?#153764 04/28/085:26 am04/28/085:26 am
Thanks Carlo , that one's a keeper ! This info is getting hard to find . I once had a stack of original handbooks that I regret passing along , didnt think I would stumble across some RE twins ?? Is there a CDmanual like the CD's by kim for the RE's ? I seem to recall a post a while back about something like this ? I lost a lotta files in a computer crash , dont recall who mentioned it .
On page 6 of my book, (Engine Specifications) para 9, Camshafts it says "camshafts...profiled to give racing performance ...the usual silencing ramps are omitted. Alternative cams with silencing ramps are available for riders who are prepared to sacrafice a little performance in the interest of mechanical silence. THESE WERE FITTED TO THE EARLIER ENGINES." ...end quote. So, can we assume the earlier Series 1s had regular cams and later years hi-po cams? What years had what?? I got this workshop book from a dealer who only began selling REs in 1969. The book has the red cover and is from east coast distributor Gene Shillingford & Sons. I think it is a later S1 edition because it has on page 2 a bit on "details affecting ign timing and adjustment" that talks about having automatic advance and "switcing off" the ign. as if talking about a Series 1A??? It's definitely the S1 shop book though, with a whole section on the magnito ign. Curious? Don
1965 Royal Enfield Interceptor 1969 Triumph Tiger 650
Bonzo The CD I have covers workshop stuff fairly well and includes the info that Carlo mentioned about cams & cam sprockets but it only has the one Interceptor Parts manual from 1963. It is not comprehensive in that it only includes the basic information about the RE twins. It includes info about 500 Twins, Meteors, Super Meteors, Constelations, and a cross section of Interseptor stuff. Its good to have around when you need more info than your model specific manuals cover.
I know nothing about Enfield Interceptor engines but have experimented with cams on other British bikes.
My experience would suggest the following.
Firstly if you want to be serious about this you should really obtain or borrow a dial guage and degree wheel to measure the cam profiles. The procedure is to set up the degree wheel on the crankshaft and then measure the lift of the cam at the followers or push rod at least every 5 degrees through the entire 720 degree cycle. More than half the time you will be on the base circle so you can cut down the readings there but even then sometimes you will get surprises especially on old cams.
You will then be able to answer all those questions above about lift and quietening ramps and openning and closing. You will also know what tappet clearance you really need.
You will also probably find that the standard timing marks on the cams are different to the intended design specification because of manufacturing tolerences etc. You also need to find out what checking clearances the cam timing figures assume. Many cam manufactuers in the car world use 50 thou lift but most bike cams I have seen give the number where you transition from the quietening ramp to the cam proper.
Like I said I dont know about Enfield twin but Im actually surprised they replaced an inlet cam with an exhaust. In my experience exhaust cams usually have lower lift and are milder than the inlet.
The problem with swapping and advancing or retarding cams on twin cam bikes is that you run the danger of the valves colliding. This is not an easy thing to check. I have seen people make up dummy barrels with windows in the side (No piston) so you can measure the valve clearances while the engine is turned over. Plus unless you have a low compression piston you should also check for piston valve clearance using clay on the piston top. Plus if the cam does lift higher you need to check for valve spring coil bind and retainer clearance to the valve guide.
Conventional wisdom is that retarding the inlet cam as discussed above will give more peak hp at the expense of hp at lower rpm. In fact the conventional route with race bikes is exactly the opposite and rather to advance the inlet to improve power lower down and then retard the exhaust to get back the top end. However this is not always true and only the dyno and lap times can really tell.
Books like AG Bell Four Stroke Performance Tuning give really good discussions of this topic. The tuners of the fast bikes at the front of any Classic bike race have spent a lot of time on this issue.