Bonneville America Forums Forums Technical Forums General Tech Cam question.

I have a set of early 790 cams available to me that are out of an engine that has 60,000 miles on it. The engine was well maintained with regular oil changes and valve adjustments. Would there be any issue with putting the 790 cams into an 865 that only has 6900 miles on it?

Doesn't cost much to have a Cam/machine shop check for concentricity and do a polish pass. Also, you can torque down the caps that hold your cams in place, and with a snap gauge and a mic, find out your clearances. One, one thou of an inch would be the ideal or target clearance. Or install them and drive the bike like you stole it. Depends on what you want to do.

Thanks Ryk. I don't know if you saw my post in lounge but my 03 790 was totaled out. I have an 06 865 as a replacement. I bought the 03 back from the insurance company for cheap. I figured since I already have the cams from the 03 this should be an easy swap.

I think the 790 cams are hotter than the 865. That should be a good mod.

Billy, they are. My only concern is doing a straight swap since the cams have 60,000 miles on them, wasn't sure how good of an idea it was which is why I am asking the experts.

Putting some Zinc additive in with some quality fresh oil would probably help the cams settle in. And if you want a quick fit check, plastigauge is cheap and easy. Been so long since I used it, forgot all about it. If your clearance checks came out with excessive straight up/down slop, new cam caps are available, and will tighten it up some.

Not as long as the cam owner used a really good synthetic oil and they are not available due to engine failure. If his engine did fail find out why and if the cams were starved for oil.

Wow!~ I entered my post at 11 am and just had to re-enter it!

Well, just so we are clear, the cams are coming out of my 03 790 that was totaled due to cosmetic damage. The bike still runs great and I have still been riding it. I have always used synthetic oil and changed the oil every 4,000 miles. I just purchased an 06 865 Speedmaster with 6900 miles with the the insurance payout.

I was just saying if they had been starved for oil or cheap oil had been used then you may want to check them very well. In your case I would think they should be fine.

Thanks Ian. By the way, were you ever able to source a set of high compression 865 Pistons?

Nope, just was able to have some made if I wanted but had to make multiple sets so I never persued it.

Just make sure you keep the "bucket" with the lobe it bedded in with. Nice thing about shim buckets is they keep their adjustments for a long time and you can set the clearances with the head on the bench.
Check the journals on the cam for roundness/ ovality and you can check for diametral clearance using plastigage, do this step without the buckets in so you don't force the cap onto the top of the plastigage which will then give a false reading since it will have been completely flattened by the cap.
If you do get a journal clearance that is 50% larger than what's allowed you can use emery cloth or even wet orJust make sure you keep the "bucket" with the lobe it bedded in with. Nice thing about shim buckets is they keep their adjustments for a long time and you can set the clearances with the head on the bench.
Check the journals on the cam for roundness/ ovality and you can check for diametral clearance using plastigage, do this step without the buckets in so you don't force the cap onto the top of the plastigage which will then give a false reading since it will have been completely flattened by the cap.
If you do get a journal clearance that is 50% larger than what's allowed you can use emery cloth or even wet or dry on a flat surface and polish the cap down to get the correct clearance. Yes there will be a slightly oval bore across the split but the cap takes the loading vertically not across the split.
You shouldn't have to bed the cam lobes in if you keep each bucket with its lobe, but if you want to you can put cam break in lube over the buckets and lobes. When a new cam and followers /buckets are ran for the first time you don't let the engine go below 2000 rpm for 10 minutes as this allows the cam to bed in and not dwell on the lobe. If the cam dwells on the lobe it will scuff and wear out very quickly. I didn't know this when i was younger and fired up a newly rebuilt OHC car engine and let it idle while adjusting the carb and ruined the cam by scuffing the lobes. I never even got the car on the road before having to completely disassemble the engine and inspect and clean everything and then put a new cam and followers in. After bedding in correctly the cam never caused any problems.

How did you get a 2006 with an 865 engine in it? I have a 2009 and i thought they were the first 865cc's made.

2005 was the first year of the 865 in the Speedmaster and 2007 was the first year of the 865 for the Americas. 2009 was the first year for fuel injection on the North American bikes. The rest of the world got efi in 2008.

Thanks for the info, i realized after i'd posted that it was the EFI. Wasn't aware of the cc change dates, thanks Des.

Next bike I am going to build will have the 865 but I am putting carbs on it. A member here very generously sent me a set of flat slide carbs I may use or I may put a set of old Amal carbs that came off of a Norton 850 Commando that only have 6,000 miles on them.

Australia got carbs in 2008, EFI started in2009...

Alright, to get back on track, the consensus seems to be that I should not have any problems using the cams out of my 790 that has 60,000 miles on. I think I will have the concentricity checked and a polish pass done.