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[Katies Grandad]

Can anyone tell me what the free length of the oil pressure relief valve spring should be. The one that sits just inside the oil filler neck. I'm having trouble with the motor smoking and can find nothing wrong. Rings are good and valve guides are new. I'm wondering if the top is getting flooded, which could be due to an over strong spring. That said, it's worse when the engine is pulling which indicates it is not being pulled down the guides. Any ideas.

[Tim NZ]

What year is your motor?


Do you mean the OPR for the Big-end feed on the early motors, (which was eventually deleted) or the Spring under the Oil filter? Neither of which will cause 'flooding' of the head.


If you are adamant that the rings and guides are perfect (?) then the most likely situation is that you either have an air leak 'somewhere' (Pipe in the chain case?), or the oil pump needs inspection...

[Mark M]

There are several possibilities one of which as Tim says is oil pump related where the feed gasket is mis-aligned. It's too complicated to describe the others here, there is a group especially for Crusader Owners at https://groups.yahoo.com/neo/groups/Cru ... group/info If you post there you'll get a more detailed reply. The Group is open so you can join straight away. We've handled several queries just like this recently. The oiling system on the 250s is quite complicated and faults can be difficult to fix without experienced help!

REgards, Mark

[Bullet Whisperer]

A couple more points to check - if you have the scavenge filter gauze inside the chamber with a big nut on the bottom, inside the primary case, check this filter is clear, as dirt in here will hamper scavenging of oil from the crankcase. Also, I only recently found out, on the 'Curse-ader' racer, that after the last engine build with replacement crankcases after a serious blow up, that it is possible to inadvertently mix up parts that will fit together, but which are not compatible - in my case, I had to drill a drain hole in a cam box cover I had fitted to some replacement cases which didn't drain from the back and the whole pushrod tunnel etc was filling with oil, while it vanished off the dipstick when the engine was running. I plan to fit another cylinder head to this machine, as like yours, despite all the obvious stuff being in good shape, it still smokes and uses oil - although it goes ok - and I think the cast in valve seat and plug hole 'skull' in the alloy cylinder head is very slightly loose, judging by what looks like a very slight gap around part of the join between the two materials in the combustion chamber. The engine also runs very hot in this case.

[Katies Grandad]

Thanks for the replies, unfortunately most of what has been suggested has already been checked. It is a 1959 motor with a single screw head and separate rocker blocks. It has new valve guides and new rocker gear fitted. Also a new oil pump. When I got it , it was intermittently smoking a bit but as it got worse I decided to do something about it. It appeared not to be scavenging too well so I changed the pump. Then it got really bad and I found blue silicon sealant in the feed to the rockers. I have split the engine right down and ultrasonic cleaned the crankcases. (some muppet had used instant gasket on the crankcase joint) I am now confident that all the oilways are clean and clear. The bore is at plus 20 and round and parallel. The compression rings have 15 thou end gap and the scraper a bit more but nowhere near the 1/16" gap that the book says is the replacement point.
It is now back to smoking intermittently as it did when I first got it, (before the blue stuff decided to break away and cause havoc). I can ride along at say 50mph with a wiffle out the back quite happily and then all of a sudden it turns into an Aerial Arrow. If I slow down and then speed back up it will go back to a wiffle again.
The oil feed up to the rockers is good and plentiful but I see very little returning directly to the tank which is why I asked about the return relief valve spring. (sits just inside the filler neck). The cam chest has a direct drain to the tank and there is no filter on the scavenge line.

[Mark M]

Have you read the 250 engine Rebuild article in Technical Notes on this site? Also, compression rings gap 15 thou fitted in bore?

REgards, Mark

[Rattlebattle]

I’m no expert on Crusaders and I’ve no wish to teach Granny about sucking eggs, but could it be the oil control ring is fitted upside down. It sounds more like piston/rings/bore to me that valve guide. On the other hand I once had a T140V on which the return side ball valve stuck open so no oil returned to the tank. Eventually the sump filled with oil and the motor stopped because of the oil drag. (It was dark at the time so I didn’ t notice the smoke screen. Could the crankcase be flooding because of a blockage in the return side?

[Katies Grandad]

The scavenge side feeds the rockers, so if it doesn't scavenge you lose that feed. As for the oil ring, it has no marking to indicate a top side and I have made sure it stayed the same way up when I had it off to check the end gap. That said if it was upside down, it is still upside down, if it does have a right way up.
One thing I didn't check was the piston to bore clearance. I'm wondering if it has a standard piston in a +20 bore and it's rocking. I don't think that is the case but I'm clutching at straws to come up with an answer.

[Katies Grandad]

I had the same as Rattler on a T140 as well. The feller following me got smothered before he got me to stop.

[Katies Grandad]

Well I'm buggered if I know where to go from here. I went out today and did about 8 miles of varied riding up to about 50mph with no smoke to speak of. Got to a roundabout , slowed went round it and pulled away laying an enormous smoke screen. This cleared after about 1/2 mile, then started again after the next roundabout. It just about cleared by the time I stopped at a friends house, about another 1/2 mile. Then after a couple of cups of tea I rode home, about 2 miles, through town, no smoke.
I just can't work out what it would be to cause such intermittent and heavy smoke. The only thing I can think of is that the rings are rotating and every so often all the gaps line up, but how the hell do you check that, and why would it happen.