Re-Powering a Vintage Gilson

Re-Powering a Vintage Gilson

This is breaking news so to speak and will be a little light on detail. I am going to rely on pictures to tell a lot of the story. With Gilson snowblowers in service since 1966 it was inevitable that time would march on and pose some repair problems. One such problem stems from advancements in small engine technology. The day of the overhead valve engine has arrived and along with it came obsolescence of the venerable Briggs & Stratton L-Head engine series. While repair parts are still in good supply short blocks and complete new engines are no longer available.

This problem has been mounting for a few years and we have begun to see a number of cases where vintage Gilsons have been given new life with the installation of current model engines. I have not had the opportunity to make such a conversion so I am lacking in exact technical details. Please do not contact me asking if a certain engine will fir your machine, I do not know. I will try to provide some guidelines for evaluating an engine purchase.

Speaking mainly of Briggs and Stratton engines in the 6,7 & 8 horsepower families there seems to be a lot of good news. B&S kept the same mounting pattern for the engine. This applies to both the Vanguard and INTEK engines. To my knowledge there was never a snow rated Vanguard model so focus your energy on an INTEK model. Following are some feature considerations:

Camshaft mount hole On most Gilsons there is a large tapped hole in the engine used to mount the belt retainers and in the case of the Unitrol models the traction idler arm as well. While the INTEK camshaft is located in a different spot there is an ear with a threaded hole integrated into the crankcase cover that provides this same feature.

Crankshaft Size Be sure to measure and compare. These larger Gilsons used engines with 1-inch crankshafts. Current engine models are often 3/4" but 1" can be found. Adding a reducing bushing to your engine pulley is an option. Be sure you are getting a straight shaft with a keyway. Some engines will have longer shafts and cutting the shaft is OK.

Crankshaft Height The distance from mounting base to the crankshaft center does seem to vary. Solutions include combinations or alternate belt sizes and engine spacers. Some engine sellers have pre-machined spacer kits available to make this exact substitution so be sure to inquire.

Mounting Studs As mentioned, within a size family stud locations seem to be consistent. Many vintage Gilson Gear Drive and 3 speed Unitrol models built with 5 horsepower engines are perfectly suited to run with 8 horsepower engines. To make this change will require some combination of adapter plate, spacers or welding. It can be done but it will take a little craftsmanship.

Belts As mentioned above some changes will involve refitting the machine with new, non-stock drive belts. You can learn more about belts here.
References
- B&S engine replacement guidance
  - (if link breaks: B&S.com -> Customer Service, see topics)
- Small Engine Warehouse
- Common belt specifications
- Thanks to members of The Best Snowblower & Lawnmower Forum and other owners for blazing the trail and providing images on this topic.

Gear Drive Models

This 1966 was given a new lease on life 40 years after rolling off the assembly line in Plymouth Wisconsin. This model normally has a wire rod style belt retainer but the owner added a wrap-around Unitrol guard to his machine. This was by choice, either would have worked on this engine. With a few thin shims under the engine it's a perfect fit.

UniTrol Models

This machine was originally a 5 HP model. The 3 speed Unitrol was taken all the way to 10HP by the late 1970s so this is no big stretch. You can see the traction idler arm clearly mounted to the threaded boss on the crankcase cover. I'm sure the owner is thrilled with the performance the extra horsepower provides.