ET: Engine (Twin) Robinson 105 cams or mk3's for my fast touring shadow.. ?

[nickthehod]

Hi Folks.

I know this is a large tin of worms and I have a opener here in my hand.....
I need to get some new cams as mine are loosing their bumps. I don't know what they are as were in situ when I got my shadow 25k miles ago but I would guess mk3.
I am in the queue with Gary Robinson for some new cams and would welcome peoples experience of the 105 cam. Am I stupid to even consider it?

I do a lot of European touring but also just everday normal riding including commuting at times.

I am aware that I would need full travel of 0.400" at valve stem.
Will 105 cams make it a less pleasant bike in traffic or are they a sensible mild tuning mod etc.
If this has all been discussed at length already please give me the title of the conversation to search.
Thanks folk!

 

[davidd]

I have never ran a 105 cam, as they are called. The cam became available when Carleton Palmer was racing and I remember talking to him about it. He said that it was not useful for racing (he tried it when straight pipes were legal). He said that it was great in a street bike because it was like a Mk2 that needed some restriction, thus it was a good performer with a silencer. He seemed to think that the Mk2 was best with a straight pipe and the 105 was best with a silencer.

I would be interested if the 105 users find this to be good information.

David

 

[Nigel Spaxman]

I have Terry Prince MKII 105 cams. My bikes idles and starts as well as any other Vincent I have seen. I can start the engine wearing flip flops. It pulls pretty well and sometimes I hit my rev limiter at 6200 RPM in first gear, but really the engine doesn't pull that well after 5000 RPMs. It pulls very well from down low though. The engine has 8:1 cast pistons. I have the straight through muffler. The bike was quite loud at first but once I had about 5000 miles on it it quieted down. I think that getting carbon in the muffler must have made a big difference. This cam is in no way like a race cam. John McDougal said it was like an RV cam. The fuel usage is about 55 MPG which is about as good as I usually here of from other Vincent riders. If I am on very slow roads where I am lugging it in fourth gear at 50 or 55 miles per hour the mileage is quite a bit higher.

 

[nickthehod]

I have Terry Prince MKII 105 cams. My bikes idles and starts as well as any other Vincent I have seen. I can start the engine wearing flip flops. It pulls pretty well and sometimes I hit my rev limiter at 6200 RPM in first gear, but really the engine doesn't pull that well after 5000 RPMs. It pulls very well from down low though. The engine has 8:1 cast pistons. I have the straight through muffler. The bike was quite loud at first but once I had about 5000 miles on it it quieted down. I think that getting carbon in the muffler must have made a big difference. This cam is in no way like a race cam. John McDougal said it was like an RV cam. The fuel usage is about 55 MPG which is about as good as I usually here of from other Vincent riders. If I am on very slow roads where I am lugging it in fourth gear at 50 or 55 miles per hour the mileage is quite a bit higher.

Thanks for that Nigel sound very promising, I am not sure how similar Terry's and Gary's 105 are but great info. Excuse my ignorance but what is an RV cam?

 

[Nigel Spaxman]

An RV cam is an Recreational Vehicle cam. That is what you would get if you had a Chev 350 V8 in a camper truck or something that required power but plenty of torque. Not the the cam for the same engine in a Corvette for example.

 

[davidd]

I am not sure how close the Prince cams are to a Robinson 105. I thought the cam was developed by Ian to use on a track that required noise control measures, but I am not certain that I remember that correctly.

I should have mentioned that I think the Mk3's are quite good cams for touring. They are easy starters and provide tons of torque. An excellent combination for the street.

David

 

[Bill Thomas]

I have Terry Prince MKII 105 cams. My bikes idles and starts as well as any other Vincent I have seen. I can start the engine wearing flip flops. It pulls pretty well and sometimes I hit my rev limiter at 6200 RPM in first gear, but really the engine doesn't pull that well after 5000 RPMs. It pulls very well from down low though. The engine has 8:1 cast pistons. I have the straight through muffler. The bike was quite loud at first but once I had about 5000 miles on it it quieted down. I think that getting carbon in the muffler must have made a big difference. This cam is in no way like a race cam. John McDougal said it was like an RV cam. The fuel usage is about 55 MPG which is about as good as I usually here of from other Vincent riders. If I am on very slow roads where I am lugging it in fourth gear at 50 or 55 miles per hour the mileage is quite a bit higher.

Morning Nigel, Any chance of photos and Carb' and ignition spec', Cheers Bill.

 

[passenger0_0]

I put a pair of Robinson 105 cams into my racing sidecar engine that ran on methanol. We found the engine produced excellent bottom end power but hit a brick wall at 5,000 rpm. After many months of fiddling with everything including the length of the inlet manifolds I ran it on an inertia dynamometer without air filters (large K&N) and found all of the mixture was being blown out the carbs like a fire extinguisher going off. It simply wouldn't rev above 5,500 rpm even with no dyno load on the engine! I knew the inlet had retarded inlet (opening late) but I couldn't advance it without the exhaust opening too early. Switched over to Robinson Mk2 cams and problem solved with no other changes made. Lots of revs and rear wheel 70 hp then the crankpin broke next meeting. This finding was reflected in my earlier comments about needing to advance the inlet cam as much as possible to get power at higher engine speeds. I know others have an opposite view so each to our own.
Gary Robinson makes very good cams so you're in good hands. Personally I'd stick to Mk 1 cams for a road bike just for that bottom end power (now that's going to get the fur flying!).

 

[nickthehod]

An RV cam is an Recreational Vehicle cam. That is what you would get if you had a Chev 350 V8 in a camper truck or something that required power but plenty of torque. Not the the cam for the same engine in a Corvette for example.

Ahh now I understand.. Thanks for your help!

 

[vibrac]

Is there any dimensional way of differentiating between 105 and MKII out of the bike? I have 5 Comet (or Rear) 'racing' cams in as new condition without pinions. I also have a strange set with curved followers attached by a bit of string for twenty years I have thought about untying that string and fitting them to something....