Anyone thinking of increasing the capacity of a standard 499cc engine unit? I recently purchased a set it parts, including the bored out crankcase, to take new larger 594cc cylinders and pistons. First thing I noticed was that the guy who did this had ordered the wrong spacer plate that is required to go under the cylinders and actually bought a 652cc one. I have ordered the correct one so this is going spare. I have built two engines in this way, a 594 for a Gamine owner and a 652 that sits in the back of my 500. Why would you do this? Because you can take a standard 499 engine, increase the engine capacity and still retain all of the original appearance and use the original ancillaries.
Technical Upping the power
- Thread starter Toshi 975
- Start date
Currently reading:
Technical Upping the power
jolly500
Member
Hi Toshi.
I'm coincidently busy helping someone with this exact mod - converting a standard 499 block to a 652. I have a few questions and concerns which I would appreciate your input on.
1. We've bought the 652 barrels and pistons and the 10mm spacer and are using the 499 crank and conrods. I've weighed the 652 pistons and their total weight is about 130 grams more than the standard pistons.
With that difference, did you do anything about the balancing of the engine? i'm worried that the extra weight of the pistons will cause a noticable imbalance?
2. Cylinder head. Using the standard 499 head, did you up valve size at all? Is that even possible or advisable?
3. Carb. We were aiming to use a Weber 28 from the bigger engine. I'm not sure whether the smaller inlet port in a 499 engine (26mm) doesn't need to be machined out to match the 28mm size of the bigger carb. I don't like the idea of having a 'step' there.
4. Which cam did you use - are they the same or would you prefer one over the other?
5. I'm a little concerned about the strength of the block after it has been machined to accept the 652 barrels, although I feel a bit more confident now that I know you have this working on your engine. Did you use gaskets and/or sealant above and below the spacer.
6. How much extra power would you think you have over a standard 499?
No hurry for the answers, just when you get a chance.
Many thanks
Steve
Johannesburg, south Africa
I'm coincidently busy helping someone with this exact mod - converting a standard 499 block to a 652. I have a few questions and concerns which I would appreciate your input on.
1. We've bought the 652 barrels and pistons and the 10mm spacer and are using the 499 crank and conrods. I've weighed the 652 pistons and their total weight is about 130 grams more than the standard pistons.
With that difference, did you do anything about the balancing of the engine? i'm worried that the extra weight of the pistons will cause a noticable imbalance?
2. Cylinder head. Using the standard 499 head, did you up valve size at all? Is that even possible or advisable?
3. Carb. We were aiming to use a Weber 28 from the bigger engine. I'm not sure whether the smaller inlet port in a 499 engine (26mm) doesn't need to be machined out to match the 28mm size of the bigger carb. I don't like the idea of having a 'step' there.
4. Which cam did you use - are they the same or would you prefer one over the other?
5. I'm a little concerned about the strength of the block after it has been machined to accept the 652 barrels, although I feel a bit more confident now that I know you have this working on your engine. Did you use gaskets and/or sealant above and below the spacer.
6. How much extra power would you think you have over a standard 499?
No hurry for the answers, just when you get a chance.
Many thanks
Steve
Johannesburg, south Africa
the hobbler
Distinguished member
- Joined
- Jul 25, 2012
- Messages
- 4,077
- Points
- 1,013
I can only give youmy experience from (a)working at Radbourne Racing as a young mechanic and, (b) my experiences with my own (tuned) '650' engine.
(1) the additional piston weight doesn't seem tohave any noticeable difference in balance
(2) The inlet valves can be enlarged by 2 mm---leave the exhaust valves 'as are' At Radbourne Racing (admittadly over 50 years ago!) we just refitted the original head back on to the '650' barrels
(3) The '28' IMB wasn't available back in those days, so we used a rejetted original carb---the inlet port can be opened to match the 126 bakelite spacer to improve flow.
(4) A 35/75/75/35 cam is a good choice--simply time it to the factory marks on the sprockets--but always use NEW cahin and sprocket kit. Fit NEW cam-followers.
(5) I cannnot remember us ever having a problem with the opened-up crankcase. You coulduse 'wellseal' forthe spacer-plate/crankcase interface and the thin copper barrel seal-rings between the spacer-pate and the bottom of the barrels.
(6) Not a point that you have raised, but you will probably find the spring-loaded push-rod tubes will seal better, look better and are definately easier to fit . You can have the head fitted on the head-studs and almost down to the barrels before you need to fit the spring-loaded push-rod tubes, they will compress that much---springs at the TOP.
If you would like to contact me direct, I have written down my thoughts on the tuning of the 126 engine (595 or 652) and you are welcome to a copy--
[email protected]
(1) the additional piston weight doesn't seem tohave any noticeable difference in balance
(2) The inlet valves can be enlarged by 2 mm---leave the exhaust valves 'as are' At Radbourne Racing (admittadly over 50 years ago!) we just refitted the original head back on to the '650' barrels
(3) The '28' IMB wasn't available back in those days, so we used a rejetted original carb---the inlet port can be opened to match the 126 bakelite spacer to improve flow.
(4) A 35/75/75/35 cam is a good choice--simply time it to the factory marks on the sprockets--but always use NEW cahin and sprocket kit. Fit NEW cam-followers.
(5) I cannnot remember us ever having a problem with the opened-up crankcase. You coulduse 'wellseal' forthe spacer-plate/crankcase interface and the thin copper barrel seal-rings between the spacer-pate and the bottom of the barrels.
(6) Not a point that you have raised, but you will probably find the spring-loaded push-rod tubes will seal better, look better and are definately easier to fit . You can have the head fitted on the head-studs and almost down to the barrels before you need to fit the spring-loaded push-rod tubes, they will compress that much---springs at the TOP.
If you would like to contact me direct, I have written down my thoughts on the tuning of the 126 engine (595 or 652) and you are welcome to a copy--
[email protected]
Hi Steve
I have never worried about engine balancing myself, I have concentrated mainly on assembling things properly and to my satisfaction. As for the conversion this has been going on for years. I have a 795cc Alquati engine that was prepared by an Italian specialist in London in 1984. I was told that the guy that did it left the Alquati racing team in Italy bringing the technology to Italtune. As it was expensive only a few engines were prepared I believe and over the years I have heard of two other engines and the possibility of a fourth. The big bore kit did not require a spacer as the work was done on a 1972 594 engine so it has no extra strengthening but the cylinders are a light press fit into the crankcase to help form a seal as there is no real land to seat the gasket after the crankcase boring.
So when I built my 650 on the 499 crankcase I used a quantity of good silicone sealant under the spacer then a gasket on top of the spacer.
I had already had a lot of work done on the cylinder head by a motor cycle racing specialist which involved the larger inlet valves, valve modifications, porting and enlarging the inlet port to 30mm in line with the 126 so I could use a 28IMB carb. This went back on the stock 499 for a while and allowed to rev in excess of 6,500 rpm which exploded my standard fan. Before using the 499 head on the 650 upgrade I gave it back to the specialist with a 650 head gasket to check for and eliminate any potential hot spots. I did not skim the head but did use the 0.5mm copper head gasket.
I went for a late series 126 camshaft (not el) for a little extra.
No idea of power but it was nice to be able to accurate up reasonable inclines
The 650 spacer plate is now sold to a forum member so I have have the bored out crankcase for the brand new 594 cylinders with new pistons. Con rods are fitted and I have purchased the required correct 594 spacer plate from Italy. I can supply a reground crankshaft complete with bearings which would make a very good basis for an as new engine. I also have a 594 tuned cylinder head that was prepared by specialists in Italy and I know from experience that it works very well with a sport camshaft. Let me know if interested.
Hi Steve
I have never worried about engine balancing myself, I have concentrated mainly on assembling things properly and to my satisfaction
Like I said at the start of December I like to do things my way. I started a little preparatory work prior to building the engine for a buyer. The engine had been assembled and described as completely rebuilt but the guy I bought the bits off said he was not happy about a few things on the engine so he stripped it down again then it got left. So apart from having the wrong spacer plate I found that one of the oil jets on the con rod was blocked which would have starved the cylinder wall of oil , the piston ring gaps were not spaced out and worst of all one of the brand new pistons had been fitted to the con rod with the gudgeon pin offset the wrong way around.
