Hi,
I have just started my first engine rebuild (1996 FD3S JDM), after a front crankshaft bearing problem, and need a bit of advice regarding the rotor side seal to corner seal clearances.

I was intending to re-use all the original seals and after re-fitting the seals in the rotors measured clearances ranging from .005" to .012" which are all within the .016" maximum clearance.

Would you replace some or all of the side seals?

Regards
Pedr0

 

If they are in good shape with no chips or unusual wear-

I would rotate them down into the shorter slots clearanced to the tightest spec and replace the one or two sideseals for the longest slots.

 

Thanks BlueTII,
I will try that first thing tomorrow

 

I found that a lot of the clearance comes from the corner seals getting notches worn into them. Install the corner seals upside-down for measuring purposes and check the clearances again.

I consider new corner seals to be critical for engine rebuilds because of that issue.

Personally... I have done a bunch of sketchy "rebuilds" but I won't go over .008" before biting the bullet and getting new side seals. Likewise, check the seal HEIGHTS. If the side seals have more than .002" difference between the middle and the ends, just replace them. I've never seen a spec for side seal height. I'd like to say that new is .118" but I forget. The taper is more critical, anyway, and I've never seen a seal that was worn "short" that didn't also have a lot of taper.

 

Thanks peejay

 

I have tried moving the seals arround for best fit and the gaps now range from 0.006" to 0.008".
I have also checked the height, straightness and thickness of all the side seals.
All the heights measured at each end and the middle of seal were within 0.0005"

The height of the seal in the technical data is 0.118"(3.0mm) mine were between 0.1195" and 0.1205" The three new seals I have are between 0.1205" to 0.121"
Thickness measured at each end and the middle were all within 0.0005"
Checked two seals back to back all looked visually straight.

I have just been offered a used set of side seals at a very good price which I am seriously considering purchasing as if only 3 or 4 give me gaps equal or better than .006" then with the 3 new ones I will have a set with a maximum of .006"

Thanks for all your comments

 

the side seal gaps open quicker than any other inside the engine so the tighter the better.

 

Thanks everyone

 

The last engine I built was built to .0015" tolerance (fifteen ten-thousandths) and had noticeably more compression when cranking. I did a lot of other changes compared to what I normally do engine-wise, so I can't say for certain that the tight gaps helped, but the engine had LOADS more low end and mid range power.

As a rule of thumb, the better the rotor's sealing ability, the better your low end and midrange power will be. This is the corollary to how a worn out engine will still have acceptable top end power but the bottom end will be all but useless. This is the downside of having the engine cycles so long (50% longer than a piston engine's), it's more time for leakdown past the seals to occur... and there is a lot of sealing surface available for leakdown.

.006-.008, I'd throw it together if I was on a budget/in a hurry.

 

going that tight is ok?

 

Yes, on an NA and as long as you confirm there is no binding between cornerseal and sideseal in extension/retraction you can run basically no measurable clearance.

You can run that tight on a turbo as well, but I would recommend a break-in if you do that will slowly work up to reaching peak loads.

Basically, you will wear the gap bigger in break-in so you don't have binding when you blast the rotors with turbo EBP under load.

If you build it to factory min. tolerances you won't have to think about anything or take extra precautions. Its consumer safe.

 

Thanks everyone for your replies,
The manufacturers data is set for technical reasons which we are not party too, I have recently retired after 48 years as a design engineer with a large diesel engine manufacturer and have seen the results many times of not complying with the manufacturers sevice manual/technical data. So I personally wouldn't go outside the manufacturers limits as you definitely run the risk of breaking something particularly if you load the engine above that for which it was not designed. The seals are long and thin and will heat up and expand a lot quicker than the rotor thus reducing the clearances with a cold engine, I have read several threads where the gaps were set to the minimum and have ended up with broken seals
My original question was regarding seal gaps whilst within the manufacturers limits are on the larger side, to find out whether there is any detrimental effect from doing so. I was hoping that I might get a reply from someone who has rebuilt an engine without doing work on the side plates or replaced apex seals etc. so that if there were any detrimental effects they could be definitely be directed at the side seals

Thanks again