Advance/Retard 5 Ton Gasser

[m139h2otruck]

We have never been real happy with how the water truck goes on the road. It never got up and went, like others have described on the site. Since it was in the high 30s and 40s on Saturday, I made a jumper for the spark plug and decided to check the timing. The original distributor was broken at the neck where it goes into the governor housing so we had to get an new rebuilt from the guys down south as I could not buy just the housing. It was installed and quickly tested with a light and set at about spec (5 BTDC). When I wasn't happy with how the truck ran, I added a little more timing (I thought!!) and have been running it the same since.

Warmed up the truck, installed the plug and jumper and ran the light. Timing at idle was at least 20-22 BTDC! Reset to 5 BTDC and truck idled OK, but would not rev above 1800-2000 with no load! Back up on the front (only problem with these things is that every thing is 5-6 feet up and down) checking again, and tried to rev motor and check timing at the same time. The mark would move backwards (towards TDC) instead of away like it should. The rebuilt unit was backwards!!

Removed the distributor and got the old one out of storage and looked at the advance plate/cam/weight assembly under the point plate. They were mirror image instead of the same. Obviously, this setup was built to go in either direction and I got the wrong one!
Took everything apart and installed the old shaft/advance unit (which was in better shape than the "rebuilt"one), reinstalled in the truck (after falling off the front bumper!), and quickly timed to 5-8 BTDC at 8:30 that night.

After the Lowell Military show on Sunday, tried the truck on the road. Great difference!! Now the thing revs right up (would go past 3,000 rpm if I wanted, so we have to check the governor) and gains speed quickly in all gears even 5th. Now the truck goes fast enough to be a little scary on the 1961 bias tires. Next upgrade will have to be 1400x20 XL radials.
Thanks for listening.

 

[acetomatoco]

Good Job..you can advance the timing until it pings a little..then back off a couple of degrees...It was specd to run 68 octane, so normal stuff now is super for it... lead additive replacer will help some too... We shaved the heads on one of ours and got about 20 more HP and more torque...don't overrev her though or the bottom end will go away ...ACE

 

[m139h2otruck]

I don't think I would run the engine above 2800-2900 rpm on a regular basis, like you said rpm is the killer of big heavy engines like these. Since the truck will be on a job without me, I have to make sure that the governor works and limits top revs to 3000 or less.

The thing now really sounds better and much quicker on revs than before. The center exhaust manifold section has a crack where the back section plugs in and the leak is really noticeable. I have a parts truck still in Clinton, Mass. that we still have to get, and we will change out the manifold as a set then.

 

[m139h2otruck]

Interesting that you cut the heads on the R6602. Somewhere, I don't remember, I read that these engines were a little problematic in the area of head gasket sealing. Was there enough "meat" in the deck surface of the head to accommodate a radical cut (0.100"+) so that there was a noticeable change in compression? Also, with the antique design of the chamber, you would not want very high compression as it would be detonation prone on regular gas (87) at anything above 7.8 or so, at least in my thinking. Most of the more "modern" gas truck engines had/have compression ratios in the range of 7.9 to 8.3 or so but with more up to date chamber designs.

 

[JasonS]

Your rebuilt disty was probably for the deuce OA331 gas engine; they spin the opposite direction and look very similar. IIRC, Vermont Commercial Salvage had reasonably priced rebuilt R6602 distys.

 

[OSO]

Hey thanks for the tips I have one of those 6602 Gas engine haven't driven it much yet just got plate last week. Now to get insurance on that beast.OSO