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#115143 25/04/22 04:51 PM
Joined: Apr 2022
Posts: 4
nathojg Offline OP
Novice
Hi all

I'm trying to fix up an old rover mulcher. Found a 6.75hp Briggs (121602-0528-E1) from a John Deere mower which I was working through adapting, first thing was to try to get it running.

It seems unnecessarily difficult to start - if it doesn't fire up on the first couple of pulls, it gets very hard to pull the cord. If you pull the spark plug it has a fair bit of oil on it, so I expect that's causing that. When it does run, it misfires, and intermittently blows grey smoke. I'm not quite sure, but I suspect there's also a tapping bearing. I'm used to diagnosing this sort of thing on cars, so not quite sure what it sounds like on these. The other thing that didn't seem right to me was the crank end float - while I didn't measure it, there's a noticeable amount.

Here's a video of it running. Reckon it's worth trying to save this thing?


Still need to adapt the blades to the crank - while the crank diameter probably be ok, the keyway needs to be enlarged. And the fuel tank will need to be moved to allow the chute to go back on. In retrospect, this motor probably wasn't the best choice, but I had a very had time finding anything 5hp or more locally.

For those curious about the original motor (130901-0625-01) - it was seized. It freed up very easily by turning the motor over with a spanner, but when trying to get it running it would only chug a couple of times after pulling the cord. Comp tested and it has only 30psi compression.... Also, less than 100mL of oil drained out (of the 800mL it takes) so I suspect it's not worth saving, but I haven't dismantled it.

Thanks
Nathan

Joined: Jan 2016
Posts: 7,467
Likes: 143
SENIOR TECHNICIAN
Sorry Nathan, no Briggs is worth repairing

1 member likes this: Mowerfreak
Joined: Sep 2015
Posts: 2,059
Likes: 146
SENIOR TECHNICIAN & HISTORIAN
G'day Nathan and Norm

I will just start a list of things that people can get mixed up when doing engine swaps.

1 The motor looks like a 675 series ,that's 6.75 Gross Torque not a HP reading.

2 the original motor would be a 5 HP Briggs with a cast iron flywheel ,this engine would be an alloy flywheel. Needs cast iron Flywheel.

3 crank shaft must be the same size as the original motor.

4 Never start a biggs with an alloy flywheel without a blade plate or weight on the crankshaft as there is no mass
to keep the motor spinning ,especially when starting as you get kick back.

5 You can install new rings but time wise and cost wise it's easier to buy a mower with a good engine for a engine swap.

6 Possibly cheaper to buy a working mulcher than what you will spend fixing a mulcher. I've seen them from $50 to $350 for a
complete Rover 5 Hp mulcher.

Cheers
Max.

Attached Images
Joined: Apr 2022
Posts: 4
nathojg Offline OP
Novice
Norm (and Max's 6th point), you're probably right smile Unfortunately I'm crazy enough to actually enjoy tinkering with this stuff.. but yeah, I need to draw the line somewhere.

Max,

1 I wondered that too, but the cover definitely says 6.75hp. pic attached. I've taken a quick look at the intek manual and going by pictures it's one of them.

2 Interesting point. What difference would this make in this application?

3 I've accounted for crank diameter and length, thankfully I got the part number of the 6.75 motor before buying it. It will work with the motor spaced up slightly. What I didn't check was the keyway size frown

4 Thanks, good point

5 That was my thought originally too. The motor I bought was advertised as running well, and was one of the few I could actually get a part number of before buying. This allowed me to look up the crank length/diameter.


I just partially disassembled the old 5hp motor. My theory about the piston expanding and seizing was right, the cylinder wall is junk. As expected, the bottom of the crank case was full of debris. What I find most interesting is that I can't see where this is from... the big end bearing was fine, which is what I'm used to seeing damaged with car engines. Some minor wear on the cam lobes. Perhaps it's all from the cylinder wall? Haven't pulled the crank yet. A couple of pictures attached for those that may be interested.

Attached Images
5hp crankcase.jpg (320.39 KB, 44 downloads)
5hp cylinder wall.jpg (242.26 KB, 43 downloads)
6.75hp cover.jpg (40 KB, 43 downloads)
Joined: Apr 2014
Posts: 219
Likes: 10
Apprentice level 3
Garden chippers are notorious for being time saps for repairers. The light to medium duty machines are generally not very well engineered and users frequently fail to respect the limitations of the equipment they have. When you add in the fact they are often infrequently used and then infrequently maintained it makes for a perfect storm of trouble.

It looks like that engine both didn’t get regular oil changes and was run with insufficient oil. Those older brigs engines stood up to years of use if given regular maintenance and treated with some mechanical sympathy.

Joined: Apr 2022
Posts: 4
nathojg Offline OP
Novice
it's been in the family for years, likely since new. i'd say it never had an oil change. looks like it was just slowly weeping from the lower crank seal. amazing it lasted this long really.

Joined: May 2010
Posts: 304
Likes: 22
Apprentice level 4
These old rover mulchers have fairly big design limitations. They are as they say a Mulcher, not a wood chipper. Also blades are stupidly expensive to get a hold of. I know from experience throwing a larger branch in just stalls it and shears the flywheel key. Depending on you're intended use I would be looking for something a bit more modern. I have one for my collection but that's about it.

The early briggs 5hp had an aluminium cylinder, no liner, so with a lack of oil the piston picks up on the bore. There are still plenty of proper 5's out there, just have to find them.

Joined: Sep 2015
Posts: 2,059
Likes: 146
SENIOR TECHNICIAN & HISTORIAN
Hi nathojg

Yes I hadn't seen the front of the motor to see if it was the OHV motor.

The cast iron flywheel would help the motor from stalling under load and loosing too many rpm.

From memory there is a step in the lower crank for the Rover mulcher.

The last Rover Mulcher I repaired was sold for $250. ,I just throw them out if the motor
is burning oil.

With second hand engines if you can't see them apart or running then you shouldn't pay anywhere
near what an inspected good running motor will be worth.

I see people throw out mulchers that were over $1000. new that just need rings or a new 7 hp $175 motor.

There are a few on eBay for around $200. but have seen them for $50. at garage sales.

Cheers
Max

Attached Images
Joined: Apr 2022
Posts: 4
nathojg Offline OP
Novice
Thanks for all the help guys.

I decided I'd have one more go at this... I think it worked out ok. Found a non running mower with a Quantum XE 45, 15 minutes away, for $35 . They said it ran only months before, it was full of oil, not seized, had compression, and unlike most sellers, they were happy to give me the part number of the motor so I could look up the crank specs before going to pick it up. I did a comp test (90psi), cleaned out the carby, and it fired up and ran perfectly, just has a leaking needle and seat.

Modified the mulcher so the motor would sit at the right height, and it all mounts up OK. Surprisingly, the fuel tank even clears the chute - I was pretty certain I'd have to make it sit on an angle to clear, that would definitely have been needed with the intek. Anyway, it seems to work OK. Maybe a bit down on grunt compared to the original motor - I never used it - but it's working for what I need it for, and it's cost very little. Might modify the starter so the rope comes out to the side.

As for the 6.75hp Intek - I ended up mounting it in the chassis the Quantum came in, and attaching the weight/blade to the crank. It definitely cranks far easier with the inertia from that. It still misfires a bit while running, and blows smoke, but given what I've seen lately, it's probably a blown head gasket rather than rings. I'll pull the head and pan off sometime to check the condition of it all and decide whether or not it's worth putting new gaskets in.


Attached Images
mulcher.jpg (325.55 KB, 12 downloads)
Last edited by nathojg; 14/05/22 04:56 PM.

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