The Stovebolt Site Forums The Shop Area Engine Shop Front Motor Mount Clearance - Important today?

I seem to be getting conflicting signals on this front motor mount assembly clearance. Can some of you In-Liner experts comment on this topic? Even if you aren't an expert that's okay.

I've spent an incredible amount of time researching the parts description, procurement, and assembly (see my posting on the 235 Front Motor Mount Details ) of this seemingly simple component. Realizing that the front mount is more or less for maintaining engine alignment verses absorbing torsional load my second question is basically two fold:

1. Is the 3/64 to 5/64" clearance important with today's butyl rubber compared with yesteryears rubber. And what does this 1/32" tolarance accomplish?

2. Is the forward weight of the engine borne by the engine mounting plate (the plate behind the timing cover) and the mount bushing to frame; the mounting plate and rubber mount to frame; or the engine mounting plate/mount plate(3657522)/retainer to frame?

I would really like to see some dialog on this topic.

Thanks,

Don

Don, go over to the oldgmctrucks.com and do a search for front motor mount. There is a guy over there that is remanufacturing the rubber front motor mount in POLYURETHANE, impermeable to oil and better shock absorbtion to boot. I just replaced mine today and the rubber was shot, we're talking about a gooey, gummy mess. The original rubber insert ('56 engine in a '49 3100) was replaced with a reman. from a parts supplier only eight years ago, 36K miles. This is one area where it is wise to go with the new stuff IMHO.

Sorry that I can't answer question #1 as I will not sweat over +/- 1/32". As far as #2...I truly believe that the front of the engine 'floats' on the polyurethane bushing (inner bolts) the assembly secured via the outer two bolts. In addition, I think you are dead spot on in your reasoning, "Realizing that the front mount is more or less for maintaining engine alignment verses absorbing torsional load...".

Cheers, Cosmo

The poly motor mount was made by AD-Engineering but don't know if they still make them.
www.ad-engineering.com

Thanks guys,

I went over to oldGMCtrucks site and it appears that the poly mount was the hot item in 2004 but for reasons unknown at this time the thread petered out. I've got a phone message and e-mail in to AD-Engineering and will post the findings if and when I obtain them. I had previously run across the topic of the poly mounts here also.

I would still appreciate more discussion on the clearance situation as described in the Shop Manual. This topic was discussed some over at Old GMCtruck site and it was mentioned that careful attention should be paid to this area.

Don

Got a call from AD-Engineering and was informed that they don't make them anymore because most folks baulked at the $40 cost

From what I've read I would have paid the cost myself to obtain a mount that will last my lifetime.

Don

Isolation is the name of the game. In the older Chevy trucks with a solid frame mounted steering column, 1/4" thick front cab mounts, a single front mount, and no transmission stick dampening, you were subject to an advanced "feel" for suspension bumps and engine vibration. Modern machines use a variety of isolators to keep vibrations to a minimum. Rag joints, fat body mounts, liquid filled engine mounts are just a few of the "improvements" that have come about in the past 50 years.

Personally, I want at least as good vibration isolation as was offered in the 50's. I've noted in my quest for making something that worked good even better, that the front mount clearances DID make a difference in the level of vibrations we feel in the cab. If you fail to establish at least the minimum clearances you will experience annoying vibrations.

The replacement rubber inserts that are offered appear to be slightly thinner than the originals. Checking to make sure that your front clearances are met or slightly exceeded will make your driving experience a good deal more pleasurable. I mentioned it in an earlier post and think it is noteworthy to repeat it again! If the 1/8" thick top floating plate that sits on the rubber mount, makes contact with the base, there will be a noticeable transfer of engine vibrations. If the rubber insert is installed upside down, there will be noticeable vibrations. If the large thru-bolt that attaches the mount to the motor plate isn't centered in the oversized holes in the cross member there will be a transfer of vibrations. Three very easy ways to diminish your driving experience. Three things that are easy to get right the first time, before you get everything buttoned up and are ready to cruise.

Admittedly, I found this out the hard way, and feel that an extra word of caution might be in order. Making corrections after your truck is on the road is not a simple proposition. If you take a little extra time to make sure that you understand the way the original system was designed to function and insure you meet the minimum clearances you'll have a much more pleasurable experience. I hope this helps.

Dave

when i put a new mount on mine i had to also add a metal shim so the pully wouldnt rub the frame

Well said FLA54. I need to apologize, I bought that poly mount years go and just put it on the other day.

Thanks Dave for the sit-down talk; I'm on the same page with you and will make sure this thing is installed to specs. The forward mount has stalled my project for another 2 weeks while I searched out another retainer and await it's delivery. T-Ruck was kind enough to send me a used one, but the other day my guy up the road thought it would be brilliant to have it machined down to look nice; He had 1/4" milled off the top to square it up with the resultant outcome that the clearance is excessive Yaaaahaaaaaa.

After spending many hours trying to find another retainer Barry Weeks came though with a NOS one and Helen at Obsolete Chev came though with a complete NOS front mount kit. Also, despite my instructions, the engine remanufacturer, and then my shop guy, did not insert the carriage bolts in the engine mounting plate prior to installing the timing cover and balancer, so it was off with the radiator, balancer, oil pan, etc. to do it correctly. The 7/16-14 bolts went missing too, and I finally found replacements at Bolt Depot.com which is a good resource for hard to find bolts. The project is now on hold awaiting the mounting parts.

I'm going to shove the "on the road in 2 weeks" statement out at least another 2 weeks :hammering: For the first time during this project I am starting to get impatient, as I would really like to make the KC meet in early September.

Cosmo - no apology is necessary. You didn't buy a spare did you? LOL

Have a good 4th and remember what Independence Day was really about.

Don