ls swap engine mount fitment issues

[TA_C10]

Hey guys, 1970 c10 ls swap. Having fitment issues. I purchased the adapter plates from LMCTruck, and am currently using the stock rubber engine mounts and stock small block perches with the truck.

I went to test fit the engine yesterday and wasn't able to get the engine mount bolts to line up. I could get the driver side bolt in but when the passenger side laid down on the perch, the engine mount setup is too wide and doesn't allow the engine to sit all the way down in the perches so I couldn't get the engine down far enough to line up the hole for the bolt.

The perches are currently installed in the front mounting location on the cross member. Its where the previous 350 was installed.

What am I doing wrong, and how can I fix this issue? We tried everything we could think of to get the engine to squeeze into the perches but no go. It needs about 1" more to slide down into the perches. Seems so close but won't go in....

We had a thought to "slot" the perches bolt hole up a little on both sides to allow the holes to line up with the mounts but not sure if this is a good idea. The engine is going to sit up higher also because of this problem. Hopefully this won't cause any issues.

Only other option I can think of is to buy new ls swap perches and motor mounts to get around this issue.

If the original rubber mounts were thinner, it would allow it to slide down into the perches and fit. But I don't see anywhere I can get thinner motor mounts....

Thanks,
Tom

[Macdaddy1]

Can you post some pics. I used speed engineering LS motor mounts and the standard stock perches with new poly motor mounts and it fit perfect.

[TA_C10]

Sure thing. This is what it looks like.

First picture is the driver side, I can get it to lineup and bolt started. Mind you everything is left loose to get this to work. Perches are loose installed, motor mounts, etc.




This is the other side, won't go down far enough.

[TA_C10]

These are borrowed pictures btw. I'm not using a 6.2L, mine is a 5.3 Gen IV vortech, LM7.

[Jstock85]

I had similar issues with ITC plates. Couldn't get it to work ended up going with the slider mounts from dirty dingo and got a perfect fit.

[TA_C10]

I bought the LMCTruck slider brackets, those aren't the issue. The issue is the engine is too wide it seems which means its too wide to fit in the factory 350 perches.

But then also the factory exhaust manifolds wont fit either, or the lower mount A/C compressor, so maybe buying the LMCTruck perches would be best anyway as they raise the motor enough I thing the manifolds work... I dunno.

[71cadc10]

I couldn't get my factory 71 small block perches to work either. I ended up using a set of later squarebody 78 perches for a small block. bolted to my 71 frame...and it drops right in. Different motor mount type though, uses the big clam shell bolted to the block plate.

[Macdaddy1]

Something does not seem right. I have a 5.3 LM7 out of an 04 Avalanche that dropped in perfect. The motor was not to wide. I used the same perches that you have in your pic and speed engineering ls mountsw with new poly motor mounts. Just a thought are you sure the ls mounts are now upside down or on the wrong side.

[truckdude239]

I used stock sbc mounts and towers with dirty dingo slinders had no problem

[dec010974]

I used that same setup w/o any problems.🤔

[Hawkynz]

Hi, I just put a 5.3 in my 1970 frame over the weekend. I used the factory 6 cylinder perches and it fit fine with a little tweeking. I used some eBay adapters that were actually really high quality for $25. No need to go buying expensive mounts or adapters. Here are some pics. It's just a mock up.

[TA_C10]

I don't think they are installed wrong. LMC adapter plates have a plate that bolts to the block, a second plate bolts to first plate that allows side to side sliding, then the stock style engine mount rubber pad bolts to second plate.

It's interesting I call LMC and wait on phone for 30 minutes till someone answers and they tell me they don't have a tech department that can answer my questions. What's up with that?

[dec010974]

junk that trash and buy some adapter plates from ebay. many vendors sell them and they move the engine froward and backward. good luck.

[72MARIO]

Have you tried loosing the frame stands off ?

I have used both dirty dingo and ebay steel adapter plates with stock v8 engine stands no problems. I did not use the low ac pump.
While you into motor mounts toss the rubber mounts in the trash and buy some poly mounts. My rubber mounts only lasted a few months.

[michael bustamante]

are you using the small block perches or in the 250 perches or the 292 perches?

[TA_C10]

It has a 350 in it so they should be the sbc perches.

[Hawkynz]

I used 250 perches. It mounts the best in the rear holes. I have tried moving it to the forward holes. It fit but had to finess it. I haven't decided exactly where I want to set it permanently. Currently I am having transmission hump clearance issues and do not want a high hump.

[Duncan K]

I experienced the same thing using the mounting plates from Speed engineering. I ended up moving the mounts out to the outsides of the frame rails a bit to make the opening wider

[prodjay10]

Originally Posted by Hawkynz

I used 250 perches. It mounts the best in the rear holes. I have tried moving it to the forward holes. It fit but had to finess it. I haven't decided exactly where I want to set it permanently. Currently I am having transmission hump clearance issues and do not want a high hump.

What’d you end up doing?
Posted via Mobile Device

[Hawkynz]

Definitely going with a high hump. No way around it. The 6l80e is tall. The trans cross member from POL or CPP, cant remember, needs to be modified to get the correct angle for the drive shaft. Another member has a post about modifying it. Essentially it sits too low.

[TA_C10]

I forgot about this post. Just to complete it, here is what I ended up doing. I couldn't get the SBC perches to line up correctly. So ended up going with tubular setup aftermarket from Performance Online. They fit great out of the box. I drilled one of the holes(bottom I think). I ended up in the rear most holes which also works out great.

Pics for your viewing pleasure