My Tractor Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
41 Posts
Discussion Starter #1
Hi guys, im new to these forums. Ive recently restored a 1960's Masport Rotacut and noticed something odd with the engine blocks. pcamore suggested i ask this on here, so here i am. What ive noticed is that some engines have an extension on the bottom of the block that helps support for the crank shaft and other don't. Ive got two d400's and two d500's. one of each has this extension and the others don't. Given the age who knows if they are all original parts or not but i though it was odd. Any one know why this might be? Ive attached a picture showing the two engines side by side. Cheers.
 

Attachments

·
4K Poster!!!!
Joined
·
5,083 Posts
Here in the states we really don't have D-500's, but all of our D series engines had the extended crankcase until 1970, from that point on only the commercial D series engines still had the extended crankcase (aka Dual bronze bushing). Our D-600's came out in 1972 and never had the dual bronze bushing. I have heard that it was just a cost savings measure to do away with them on the residential mowers.
 

·
5K Poster!!!
Joined
·
5,141 Posts
Older dual bronze bushing is the more desirable of the two. Much more strength if you were to hit something...less chance of bent crank.
 

·
Registered
Joined
·
41 Posts
Discussion Starter #4
Thanks for the info there.. maybe this D400 has been mixed and matched a little more than i thought. One advantage i noticed to the single bush version is that the oil seal is a lot less exposed so less likely to get torn up if something wraps around the shaft and blade carrier.
 

·
Senior MTF Poster
Joined
·
13,168 Posts
No problem with seals of LBs with the extension. Never had a bent crankshaft with the D400 with the extension, had lots of D600s bemt and it wasn't just the extension, the D600 crankshaft was not nearly as stiff.

Walt Conner
 

·
Premium Member
Joined
·
1,481 Posts
Question.... D500....What is the difference between the D400 and D500 engines? Like Lawnboy77 noted, we do not have D500 engines in the States. I just found the answer ... Lawnboy snow blowers of the 1980 era, model 1851 and 1871 use D500 series engines. Model 1851 is listed as using D572 engine. Crankcase on these had caged needle bearing on bottom as well as caged needle bearing in magneto plate on top. This would seem to confirm the needle bearing on bottom as being the difference. Snowblower engine also had priming port drilled into crankcase and short crankshaft like the loafer crank. This would be the be the 72 number version of the D500 engine. So we did have D500 series engines in the States. Bill
 

·
4K Poster!!!!
Joined
·
5,083 Posts
Yes it's just funny to me how Lawnboy made drastic changes over the years in regards to the D400, like doing away with the dual bronze bushing in 1970, also went to the all needle bearing connecting rod and 2 ring piston in the same year, but it still kept it's same D4XX. Then in the early 80's they make only 1 noteworthy change to the shortblock by Installing needle bearings in the lower end of the crank and now it's a D5XX. I'm guessing the reason it changed was because they were mostly being used in the snow blowers.
 

·
Registered
Joined
·
1,396 Posts
Yes it's just funny to me how Lawnboy made drastic changes over the years in regards to the D400, like doing away with the dual bronze bushing in 1970, also went to the all needle bearing connecting rod and 2 ring piston in the same year, but it still kept it's same D4XX. Then in the early 80's they make only 1 noteworthy change to the shortblock by Installing needle bearings in the lower end of the crank and now it's a D5XX. I'm guessing the reason it changed was because they were mostly being used in the snow blowers.
If only they had made the change from lower bushing to bearing earlier, there would have been more of these mowers saved from the scrap heap. I'm sure the people who had bushings go out just bought a new mower when they found out how much money it would cost to basically replace the entire motor.
 

·
Premium Member
Joined
·
1,481 Posts
I always look for free or cheap snowblowers with these engines on for the crankcase with the lower needle bearings. Makes good long life crankcase for D400 engine mowers as well as D600 ones. All you have to do is remove the small fitting that was used for the primer hose and plug the hole and you have a great heavy duty crankcase. Bill
 
1 - 9 of 9 Posts
Top