Question: Can I use a 4 Stroke engine on my VMAR ARF model?
Answer: In most cases, Yes.
Better Answer: There are some things to consider here. First of all if the model has a cowl it will usually have a power module consisting of a removeable forward firewall and a set of engine mounts. These engine mounts can be oriented in many different ways so you can select the orientation and separation of the mounts to suit your engine. It is also very easy to work on with this setup because the forward firewall is completely removeable from the model. So... VMAR models with a cowl and power module probably will be able to accomodate a 4 stroke engine. Conversely... models without a cowl and power module usually have a factory installed engine mount and a fixed firewall only and may be more problematic when trying to fit them out with a 4 stroke engine. It is safe to say that if the model does not have a cowl and power module there may be significant work and mucking around in order to install a 4 stroke engine.
4 stroke engines are not as standardized as most 2 stroke engines... some have the carburetors at the front, some at the back. Some have valve pushrods running up the front of the crankcase... some up the back. As a consequence, 4 stroke engines vary quite a bit in length (i.e. the distance from the prop shaft to the back of the engine) within a particular size. Although for example a 2 stroke .46 from one supplier will be very similar in external size to that of a 2 stroke .46 from another supplier... it is not necessarily the case when comparing 4 strokes. A .52 four stroke from one manufacturer can be quite different from a .52 four stroke from another manufacturer. There is no way we can be aware of all the different sizes and shapes of four stroke engines in the market and modelers should be checking with the engine manufacturer for sizes before assuming that the engine will fit into any particular model. Once you know the length of the four stroke engine that you are considering, place the cowl on your model. Then measure from where the back plate of the spinner will be to the front face of the removeable power module firewall. Subtract about 1.25" from this distance and then compare the result with the length of your four stroke engine. Engines that exceed this length will significantly protrude from the front of the cowl and should be trial fitted carefully before purchase.
In some cases, we are pre-cutting cowls to make installation of our recommended 2 stroke engine go as quickly and easily as possible. We do stock blank (not cut) cowls for those who wish to use a differnet 2 stroke engine size (for example a .61 instead of a .46) or a 4 stroke instead of a 2 stroke or want to go with an inverted installation or other orientation when we may have assumed a 90 orientation when pre-cutting the factory cowl.
Lastly, we have some models that do not use a cowl per-se and do not have a power module but may look like they do. For example the F4U Phantom and Skyhawk and Arrow Tiger have a shaped and fitted nose section but not a cowl and we have not recommended 4 stroke engines for these models at all. Again, if we do not use a cowl and power module on a model... we may be significant work and mucking around in order to install a 4 stroke engine.
Please note that to this point this article makes no attempt to explain the differences between the different types of engine systems. For some of the pro's and con's of 2 stroke and 4 stroke engines please the article included below: |