Sd1 (Rv8) Engine mounts

[DrFelch]

I have just cleaned up my SD1 Rover V8 engine mounts (thanks JimT !). But need to know the bolt size to go into the engine. I have a seen a posting giving sizes + torque settings of other bolts for the rover, but not these ones !!! Looks to me as they could be UNC ? Do they have to be 'high tensile'. What the hell is high tensile anyway ? What the hell is UNC ? What the hell is a bolt anyway... !!!??? bugger it...

Marcus

[STEVE G]

Marcus
Just replaced mine on new engine.You should have 3 Bolts each side.
Top one is 5/16"UNC,Bottom 2 are 7/16"UNC.I've used Stainless bolts altho I've been advised not to use s/s where they are likely to vibrate(i.e.on suspension parts)due to the fact they are not as strong as mild steel H/T bolts.
Steve Grundy

[Trigger]

Hi Marcus, what happened to the original bolts? You could reuse them or get the sizes from them for new ones. The thread on these bolts is UNC, Unified Coarse, as opposed to UNF, Unified Fine. UNC are the great majority of the bolts and screws on the RV8. Aluminium is not suitable for fine threads being too soft although fine threads can give more torque/pulldown. There are 2 sizes for the engine mounts and I believe they 3/8" for the smaller one and 7/16" or 1/2" for the 2 bigger ones. The size of the bolts is the diameter of the shank so are easy to measure and they are definitely UNC. The torque figures I don't know. I have asked this question in several forums and magazines and nobody seems to know. It's not in the Haynes manual. However every bolt has a torque figure which should not be exceeded and the bigger the bolt the more torque it can take and more pull down it can give. Different grades of bolts have different torques but the difference is not great. In aluminium you may not want to go to the full strength of the bolt in case you pull the thread that is why it is very important to use the manufacturers figures. The Haynes manual is pretty good but I think the figures for some of the smaller sizes are too high. Like the 1/4" bolts in the water pump/timing cover. They say 20ftlbs but I used 15ftlbs. I am not at home at the moment so don't have my tables to hand but I would say 25ftlbs for the small bolt and 35ftlbs for the larger ones would be ok.

Always use a lubricant when torquing bolts. I use 50% kerosene/engine oil. Always clean the threads before use. Try finger tight first to see if the thread is damaged. Always check the length of the bolt is less than the depth of the bolt hole. Very important that bit! Your torque wrench should have ftlbs and Newton Metres (NM) so make sure you are on the right scale. You can retap threads to make the bolt go in but only do this as a last resort if the thread is damaged. Usually stiffness is caused by dirt. I wouldn't use a tap to clean threads routinely as there is always some metal removed and you could break off the tap ... The depth of thread is also a factor in torquing which is a reason why I wouldn't go the full hog on the bigger bolts on the engine mounts. Last tip. Don't tighten bolts in aluminium without a torque wrench but damaged threads can be repaired with helicoils which are inserts into a bigger hole. The hole in the insert is the original size. But of course the hole might not be convenient to get at ...! There is a section on bolts/threads in the Tips on the forum front page. Trigger.

[DrFelch]

Thanks guys ! I dont have the original bolts...

This is a great help.

Marcus

[Trigger]

Hi Steve, I would only use stainless where there is no real torque requirement as you will find most are ungraded unless for very specialised use. Look good in none critical areas though and of course you can use spring washers under the head to help stop slacking off. When torquing critical bolts and especially high values you should use heavy steel washers only under the head with no spring washer. Spreads the load and spring washers crack and dig in under heavy torque loads. The correct torque figure gives the correct pull down and the slight stretching of the bolt stops it from coming loose. Marcus, when sourcing your engine mounting bolts just get the same grade as the rest of the bolts on the engine. There will be markings on the bolt head or a value in figures. Steve's bolt sizes are probably right but the torque values I gave will still be ok. As I said I am not at home so I can't get my hands on any info! Trigger

[russell_ram]

Range Rover Tech Manual - torque settings for all screws and bolts used except for those that are specified otherwise. (Engine mounting bolts are not specified specifically).

1/4 UNC 5-7 lbf ft
5/16 UNC 15-20
3/8 26-32
7/16 50-65
1/2 60-75
5/8 90-110

1/4 UNF 6-9 lbf ft
5/16 15-20
3/8 26-32
7/16 50-65
1/2 60-75
5/8 90-110

Russ

[STEVE G]

Marcus
I think I should have the original bolts at home.If I find them I will let you have them.
I will look tonite
Steve

[DrFelch]

Thanks for this Steve, but I managed to get some from my local bolt shop ! I might order some from a Rover garage today though just to be sure I have the exact ones. They will only be a couple of quid for the lot.

Cheers for your help though !

Marcus